| // SPDX-License-Identifier: GPL-2.0 |
| |
| #include <linux/kernel.h> |
| #include <linux/irqflags.h> |
| #include <linux/string.h> |
| #include <linux/errno.h> |
| #include <linux/bug.h> |
| #include "printk_ringbuffer.h" |
| |
| /** |
| * DOC: printk_ringbuffer overview |
| * |
| * Data Structure |
| * -------------- |
| * The printk_ringbuffer is made up of 3 internal ringbuffers: |
| * |
| * desc_ring |
| * A ring of descriptors and their meta data (such as sequence number, |
| * timestamp, loglevel, etc.) as well as internal state information about |
| * the record and logical positions specifying where in the other |
| * ringbuffer the text strings are located. |
| * |
| * text_data_ring |
| * A ring of data blocks. A data block consists of an unsigned long |
| * integer (ID) that maps to a desc_ring index followed by the text |
| * string of the record. |
| * |
| * The internal state information of a descriptor is the key element to allow |
| * readers and writers to locklessly synchronize access to the data. |
| * |
| * Implementation |
| * -------------- |
| * |
| * Descriptor Ring |
| * ~~~~~~~~~~~~~~~ |
| * The descriptor ring is an array of descriptors. A descriptor contains |
| * essential meta data to track the data of a printk record using |
| * blk_lpos structs pointing to associated text data blocks (see |
| * "Data Rings" below). Each descriptor is assigned an ID that maps |
| * directly to index values of the descriptor array and has a state. The ID |
| * and the state are bitwise combined into a single descriptor field named |
| * @state_var, allowing ID and state to be synchronously and atomically |
| * updated. |
| * |
| * Descriptors have four states: |
| * |
| * reserved |
| * A writer is modifying the record. |
| * |
| * committed |
| * The record and all its data are written. A writer can reopen the |
| * descriptor (transitioning it back to reserved), but in the committed |
| * state the data is consistent. |
| * |
| * finalized |
| * The record and all its data are complete and available for reading. A |
| * writer cannot reopen the descriptor. |
| * |
| * reusable |
| * The record exists, but its text and/or meta data may no longer be |
| * available. |
| * |
| * Querying the @state_var of a record requires providing the ID of the |
| * descriptor to query. This can yield a possible fifth (pseudo) state: |
| * |
| * miss |
| * The descriptor being queried has an unexpected ID. |
| * |
| * The descriptor ring has a @tail_id that contains the ID of the oldest |
| * descriptor and @head_id that contains the ID of the newest descriptor. |
| * |
| * When a new descriptor should be created (and the ring is full), the tail |
| * descriptor is invalidated by first transitioning to the reusable state and |
| * then invalidating all tail data blocks up to and including the data blocks |
| * associated with the tail descriptor (for the text ring). Then |
| * @tail_id is advanced, followed by advancing @head_id. And finally the |
| * @state_var of the new descriptor is initialized to the new ID and reserved |
| * state. |
| * |
| * The @tail_id can only be advanced if the new @tail_id would be in the |
| * committed or reusable queried state. This makes it possible that a valid |
| * sequence number of the tail is always available. |
| * |
| * Descriptor Finalization |
| * ~~~~~~~~~~~~~~~~~~~~~~~ |
| * When a writer calls the commit function prb_commit(), record data is |
| * fully stored and is consistent within the ringbuffer. However, a writer can |
| * reopen that record, claiming exclusive access (as with prb_reserve()), and |
| * modify that record. When finished, the writer must again commit the record. |
| * |
| * In order for a record to be made available to readers (and also become |
| * recyclable for writers), it must be finalized. A finalized record cannot be |
| * reopened and can never become "unfinalized". Record finalization can occur |
| * in three different scenarios: |
| * |
| * 1) A writer can simultaneously commit and finalize its record by calling |
| * prb_final_commit() instead of prb_commit(). |
| * |
| * 2) When a new record is reserved and the previous record has been |
| * committed via prb_commit(), that previous record is automatically |
| * finalized. |
| * |
| * 3) When a record is committed via prb_commit() and a newer record |
| * already exists, the record being committed is automatically finalized. |
| * |
| * Data Ring |
| * ~~~~~~~~~ |
| * The text data ring is a byte array composed of data blocks. Data blocks are |
| * referenced by blk_lpos structs that point to the logical position of the |
| * beginning of a data block and the beginning of the next adjacent data |
| * block. Logical positions are mapped directly to index values of the byte |
| * array ringbuffer. |
| * |
| * Each data block consists of an ID followed by the writer data. The ID is |
| * the identifier of a descriptor that is associated with the data block. A |
| * given data block is considered valid if all of the following conditions |
| * are met: |
| * |
| * 1) The descriptor associated with the data block is in the committed |
| * or finalized queried state. |
| * |
| * 2) The blk_lpos struct within the descriptor associated with the data |
| * block references back to the same data block. |
| * |
| * 3) The data block is within the head/tail logical position range. |
| * |
| * If the writer data of a data block would extend beyond the end of the |
| * byte array, only the ID of the data block is stored at the logical |
| * position and the full data block (ID and writer data) is stored at the |
| * beginning of the byte array. The referencing blk_lpos will point to the |
| * ID before the wrap and the next data block will be at the logical |
| * position adjacent the full data block after the wrap. |
| * |
| * Data rings have a @tail_lpos that points to the beginning of the oldest |
| * data block and a @head_lpos that points to the logical position of the |
| * next (not yet existing) data block. |
| * |
| * When a new data block should be created (and the ring is full), tail data |
| * blocks will first be invalidated by putting their associated descriptors |
| * into the reusable state and then pushing the @tail_lpos forward beyond |
| * them. Then the @head_lpos is pushed forward and is associated with a new |
| * descriptor. If a data block is not valid, the @tail_lpos cannot be |
| * advanced beyond it. |
| * |
| * Info Array |
| * ~~~~~~~~~~ |
| * The general meta data of printk records are stored in printk_info structs, |
| * stored in an array with the same number of elements as the descriptor ring. |
| * Each info corresponds to the descriptor of the same index in the |
| * descriptor ring. Info validity is confirmed by evaluating the corresponding |
| * descriptor before and after loading the info. |
| * |
| * Usage |
| * ----- |
| * Here are some simple examples demonstrating writers and readers. For the |
| * examples a global ringbuffer (test_rb) is available (which is not the |
| * actual ringbuffer used by printk):: |
| * |
| * DEFINE_PRINTKRB(test_rb, 15, 5); |
| * |
| * This ringbuffer allows up to 32768 records (2 ^ 15) and has a size of |
| * 1 MiB (2 ^ (15 + 5)) for text data. |
| * |
| * Sample writer code:: |
| * |
| * const char *textstr = "message text"; |
| * struct prb_reserved_entry e; |
| * struct printk_record r; |
| * |
| * // specify how much to allocate |
| * prb_rec_init_wr(&r, strlen(textstr) + 1); |
| * |
| * if (prb_reserve(&e, &test_rb, &r)) { |
| * snprintf(r.text_buf, r.text_buf_size, "%s", textstr); |
| * |
| * r.info->text_len = strlen(textstr); |
| * r.info->ts_nsec = local_clock(); |
| * r.info->caller_id = printk_caller_id(); |
| * |
| * // commit and finalize the record |
| * prb_final_commit(&e); |
| * } |
| * |
| * Note that additional writer functions are available to extend a record |
| * after it has been committed but not yet finalized. This can be done as |
| * long as no new records have been reserved and the caller is the same. |
| * |
| * Sample writer code (record extending):: |
| * |
| * // alternate rest of previous example |
| * |
| * r.info->text_len = strlen(textstr); |
| * r.info->ts_nsec = local_clock(); |
| * r.info->caller_id = printk_caller_id(); |
| * |
| * // commit the record (but do not finalize yet) |
| * prb_commit(&e); |
| * } |
| * |
| * ... |
| * |
| * // specify additional 5 bytes text space to extend |
| * prb_rec_init_wr(&r, 5); |
| * |
| * // try to extend, but only if it does not exceed 32 bytes |
| * if (prb_reserve_in_last(&e, &test_rb, &r, printk_caller_id()), 32) { |
| * snprintf(&r.text_buf[r.info->text_len], |
| * r.text_buf_size - r.info->text_len, "hello"); |
| * |
| * r.info->text_len += 5; |
| * |
| * // commit and finalize the record |
| * prb_final_commit(&e); |
| * } |
| * |
| * Sample reader code:: |
| * |
| * struct printk_info info; |
| * struct printk_record r; |
| * char text_buf[32]; |
| * u64 seq; |
| * |
| * prb_rec_init_rd(&r, &info, &text_buf[0], sizeof(text_buf)); |
| * |
| * prb_for_each_record(0, &test_rb, &seq, &r) { |
| * if (info.seq != seq) |
| * pr_warn("lost %llu records\n", info.seq - seq); |
| * |
| * if (info.text_len > r.text_buf_size) { |
| * pr_warn("record %llu text truncated\n", info.seq); |
| * text_buf[r.text_buf_size - 1] = 0; |
| * } |
| * |
| * pr_info("%llu: %llu: %s\n", info.seq, info.ts_nsec, |
| * &text_buf[0]); |
| * } |
| * |
| * Note that additional less convenient reader functions are available to |
| * allow complex record access. |
| * |
| * ABA Issues |
| * ~~~~~~~~~~ |
| * To help avoid ABA issues, descriptors are referenced by IDs (array index |
| * values combined with tagged bits counting array wraps) and data blocks are |
| * referenced by logical positions (array index values combined with tagged |
| * bits counting array wraps). However, on 32-bit systems the number of |
| * tagged bits is relatively small such that an ABA incident is (at least |
| * theoretically) possible. For example, if 4 million maximally sized (1KiB) |
| * printk messages were to occur in NMI context on a 32-bit system, the |
| * interrupted context would not be able to recognize that the 32-bit integer |
| * completely wrapped and thus represents a different data block than the one |
| * the interrupted context expects. |
| * |
| * To help combat this possibility, additional state checking is performed |
| * (such as using cmpxchg() even though set() would suffice). These extra |
| * checks are commented as such and will hopefully catch any ABA issue that |
| * a 32-bit system might experience. |
| * |
| * Memory Barriers |
| * ~~~~~~~~~~~~~~~ |
| * Multiple memory barriers are used. To simplify proving correctness and |
| * generating litmus tests, lines of code related to memory barriers |
| * (loads, stores, and the associated memory barriers) are labeled:: |
| * |
| * LMM(function:letter) |
| * |
| * Comments reference the labels using only the "function:letter" part. |
| * |
| * The memory barrier pairs and their ordering are: |
| * |
| * desc_reserve:D / desc_reserve:B |
| * push descriptor tail (id), then push descriptor head (id) |
| * |
| * desc_reserve:D / data_push_tail:B |
| * push data tail (lpos), then set new descriptor reserved (state) |
| * |
| * desc_reserve:D / desc_push_tail:C |
| * push descriptor tail (id), then set new descriptor reserved (state) |
| * |
| * desc_reserve:D / prb_first_seq:C |
| * push descriptor tail (id), then set new descriptor reserved (state) |
| * |
| * desc_reserve:F / desc_read:D |
| * set new descriptor id and reserved (state), then allow writer changes |
| * |
| * data_alloc:A (or data_realloc:A) / desc_read:D |
| * set old descriptor reusable (state), then modify new data block area |
| * |
| * data_alloc:A (or data_realloc:A) / data_push_tail:B |
| * push data tail (lpos), then modify new data block area |
| * |
| * _prb_commit:B / desc_read:B |
| * store writer changes, then set new descriptor committed (state) |
| * |
| * desc_reopen_last:A / _prb_commit:B |
| * set descriptor reserved (state), then read descriptor data |
| * |
| * _prb_commit:B / desc_reserve:D |
| * set new descriptor committed (state), then check descriptor head (id) |
| * |
| * data_push_tail:D / data_push_tail:A |
| * set descriptor reusable (state), then push data tail (lpos) |
| * |
| * desc_push_tail:B / desc_reserve:D |
| * set descriptor reusable (state), then push descriptor tail (id) |
| */ |
| |
| #define DATA_SIZE(data_ring) _DATA_SIZE((data_ring)->size_bits) |
| #define DATA_SIZE_MASK(data_ring) (DATA_SIZE(data_ring) - 1) |
| |
| #define DESCS_COUNT(desc_ring) _DESCS_COUNT((desc_ring)->count_bits) |
| #define DESCS_COUNT_MASK(desc_ring) (DESCS_COUNT(desc_ring) - 1) |
| |
| /* Determine the data array index from a logical position. */ |
| #define DATA_INDEX(data_ring, lpos) ((lpos) & DATA_SIZE_MASK(data_ring)) |
| |
| /* Determine the desc array index from an ID or sequence number. */ |
| #define DESC_INDEX(desc_ring, n) ((n) & DESCS_COUNT_MASK(desc_ring)) |
| |
| /* Determine how many times the data array has wrapped. */ |
| #define DATA_WRAPS(data_ring, lpos) ((lpos) >> (data_ring)->size_bits) |
| |
| /* Determine if a logical position refers to a data-less block. */ |
| #define LPOS_DATALESS(lpos) ((lpos) & 1UL) |
| #define BLK_DATALESS(blk) (LPOS_DATALESS((blk)->begin) && \ |
| LPOS_DATALESS((blk)->next)) |
| |
| /* Get the logical position at index 0 of the current wrap. */ |
| #define DATA_THIS_WRAP_START_LPOS(data_ring, lpos) \ |
| ((lpos) & ~DATA_SIZE_MASK(data_ring)) |
| |
| /* Get the ID for the same index of the previous wrap as the given ID. */ |
| #define DESC_ID_PREV_WRAP(desc_ring, id) \ |
| DESC_ID((id) - DESCS_COUNT(desc_ring)) |
| |
| /* |
| * A data block: mapped directly to the beginning of the data block area |
| * specified as a logical position within the data ring. |
| * |
| * @id: the ID of the associated descriptor |
| * @data: the writer data |
| * |
| * Note that the size of a data block is only known by its associated |
| * descriptor. |
| */ |
| struct prb_data_block { |
| unsigned long id; |
| char data[0]; |
| }; |
| |
| /* |
| * Return the descriptor associated with @n. @n can be either a |
| * descriptor ID or a sequence number. |
| */ |
| static struct prb_desc *to_desc(struct prb_desc_ring *desc_ring, u64 n) |
| { |
| return &desc_ring->descs[DESC_INDEX(desc_ring, n)]; |
| } |
| |
| /* |
| * Return the printk_info associated with @n. @n can be either a |
| * descriptor ID or a sequence number. |
| */ |
| static struct printk_info *to_info(struct prb_desc_ring *desc_ring, u64 n) |
| { |
| return &desc_ring->infos[DESC_INDEX(desc_ring, n)]; |
| } |
| |
| static struct prb_data_block *to_block(struct prb_data_ring *data_ring, |
| unsigned long begin_lpos) |
| { |
| return (void *)&data_ring->data[DATA_INDEX(data_ring, begin_lpos)]; |
| } |
| |
| /* |
| * Increase the data size to account for data block meta data plus any |
| * padding so that the adjacent data block is aligned on the ID size. |
| */ |
| static unsigned int to_blk_size(unsigned int size) |
| { |
| struct prb_data_block *db = NULL; |
| |
| size += sizeof(*db); |
| size = ALIGN(size, sizeof(db->id)); |
| return size; |
| } |
| |
| /* |
| * Sanity checker for reserve size. The ringbuffer code assumes that a data |
| * block does not exceed the maximum possible size that could fit within the |
| * ringbuffer. This function provides that basic size check so that the |
| * assumption is safe. |
| */ |
| static bool data_check_size(struct prb_data_ring *data_ring, unsigned int size) |
| { |
| struct prb_data_block *db = NULL; |
| |
| if (size == 0) |
| return true; |
| |
| /* |
| * Ensure the alignment padded size could possibly fit in the data |
| * array. The largest possible data block must still leave room for |
| * at least the ID of the next block. |
| */ |
| size = to_blk_size(size); |
| if (size > DATA_SIZE(data_ring) - sizeof(db->id)) |
| return false; |
| |
| return true; |
| } |
| |
| /* Query the state of a descriptor. */ |
| static enum desc_state get_desc_state(unsigned long id, |
| unsigned long state_val) |
| { |
| if (id != DESC_ID(state_val)) |
| return desc_miss; |
| |
| return DESC_STATE(state_val); |
| } |
| |
| /* |
| * Get a copy of a specified descriptor and return its queried state. If the |
| * descriptor is in an inconsistent state (miss or reserved), the caller can |
| * only expect the descriptor's @state_var field to be valid. |
| * |
| * The sequence number and caller_id can be optionally retrieved. Like all |
| * non-state_var data, they are only valid if the descriptor is in a |
| * consistent state. |
| */ |
| static enum desc_state desc_read(struct prb_desc_ring *desc_ring, |
| unsigned long id, struct prb_desc *desc_out, |
| u64 *seq_out, u32 *caller_id_out) |
| { |
| struct printk_info *info = to_info(desc_ring, id); |
| struct prb_desc *desc = to_desc(desc_ring, id); |
| atomic_long_t *state_var = &desc->state_var; |
| enum desc_state d_state; |
| unsigned long state_val; |
| |
| /* Check the descriptor state. */ |
| state_val = atomic_long_read(state_var); /* LMM(desc_read:A) */ |
| d_state = get_desc_state(id, state_val); |
| if (d_state == desc_miss || d_state == desc_reserved) { |
| /* |
| * The descriptor is in an inconsistent state. Set at least |
| * @state_var so that the caller can see the details of |
| * the inconsistent state. |
| */ |
| goto out; |
| } |
| |
| /* |
| * Guarantee the state is loaded before copying the descriptor |
| * content. This avoids copying obsolete descriptor content that might |
| * not apply to the descriptor state. This pairs with _prb_commit:B. |
| * |
| * Memory barrier involvement: |
| * |
| * If desc_read:A reads from _prb_commit:B, then desc_read:C reads |
| * from _prb_commit:A. |
| * |
| * Relies on: |
| * |
| * WMB from _prb_commit:A to _prb_commit:B |
| * matching |
| * RMB from desc_read:A to desc_read:C |
| */ |
| smp_rmb(); /* LMM(desc_read:B) */ |
| |
| /* |
| * Copy the descriptor data. The data is not valid until the |
| * state has been re-checked. A memcpy() for all of @desc |
| * cannot be used because of the atomic_t @state_var field. |
| */ |
| memcpy(&desc_out->text_blk_lpos, &desc->text_blk_lpos, |
| sizeof(desc_out->text_blk_lpos)); /* LMM(desc_read:C) */ |
| if (seq_out) |
| *seq_out = info->seq; /* also part of desc_read:C */ |
| if (caller_id_out) |
| *caller_id_out = info->caller_id; /* also part of desc_read:C */ |
| |
| /* |
| * 1. Guarantee the descriptor content is loaded before re-checking |
| * the state. This avoids reading an obsolete descriptor state |
| * that may not apply to the copied content. This pairs with |
| * desc_reserve:F. |
| * |
| * Memory barrier involvement: |
| * |
| * If desc_read:C reads from desc_reserve:G, then desc_read:E |
| * reads from desc_reserve:F. |
| * |
| * Relies on: |
| * |
| * WMB from desc_reserve:F to desc_reserve:G |
| * matching |
| * RMB from desc_read:C to desc_read:E |
| * |
| * 2. Guarantee the record data is loaded before re-checking the |
| * state. This avoids reading an obsolete descriptor state that may |
| * not apply to the copied data. This pairs with data_alloc:A and |
| * data_realloc:A. |
| * |
| * Memory barrier involvement: |
| * |
| * If copy_data:A reads from data_alloc:B, then desc_read:E |
| * reads from desc_make_reusable:A. |
| * |
| * Relies on: |
| * |
| * MB from desc_make_reusable:A to data_alloc:B |
| * matching |
| * RMB from desc_read:C to desc_read:E |
| * |
| * Note: desc_make_reusable:A and data_alloc:B can be different |
| * CPUs. However, the data_alloc:B CPU (which performs the |
| * full memory barrier) must have previously seen |
| * desc_make_reusable:A. |
| */ |
| smp_rmb(); /* LMM(desc_read:D) */ |
| |
| /* |
| * The data has been copied. Return the current descriptor state, |
| * which may have changed since the load above. |
| */ |
| state_val = atomic_long_read(state_var); /* LMM(desc_read:E) */ |
| d_state = get_desc_state(id, state_val); |
| out: |
| atomic_long_set(&desc_out->state_var, state_val); |
| return d_state; |
| } |
| |
| /* |
| * Take a specified descriptor out of the finalized state by attempting |
| * the transition from finalized to reusable. Either this context or some |
| * other context will have been successful. |
| */ |
| static void desc_make_reusable(struct prb_desc_ring *desc_ring, |
| unsigned long id) |
| { |
| unsigned long val_finalized = DESC_SV(id, desc_finalized); |
| unsigned long val_reusable = DESC_SV(id, desc_reusable); |
| struct prb_desc *desc = to_desc(desc_ring, id); |
| atomic_long_t *state_var = &desc->state_var; |
| |
| atomic_long_cmpxchg_relaxed(state_var, val_finalized, |
| val_reusable); /* LMM(desc_make_reusable:A) */ |
| } |
| |
| /* |
| * Given the text data ring, put the associated descriptor of each |
| * data block from @lpos_begin until @lpos_end into the reusable state. |
| * |
| * If there is any problem making the associated descriptor reusable, either |
| * the descriptor has not yet been finalized or another writer context has |
| * already pushed the tail lpos past the problematic data block. Regardless, |
| * on error the caller can re-load the tail lpos to determine the situation. |
| */ |
| static bool data_make_reusable(struct printk_ringbuffer *rb, |
| struct prb_data_ring *data_ring, |
| unsigned long lpos_begin, |
| unsigned long lpos_end, |
| unsigned long *lpos_out) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| struct prb_data_block *blk; |
| enum desc_state d_state; |
| struct prb_desc desc; |
| struct prb_data_blk_lpos *blk_lpos = &desc.text_blk_lpos; |
| unsigned long id; |
| |
| /* Loop until @lpos_begin has advanced to or beyond @lpos_end. */ |
| while ((lpos_end - lpos_begin) - 1 < DATA_SIZE(data_ring)) { |
| blk = to_block(data_ring, lpos_begin); |
| |
| /* |
| * Load the block ID from the data block. This is a data race |
| * against a writer that may have newly reserved this data |
| * area. If the loaded value matches a valid descriptor ID, |
| * the blk_lpos of that descriptor will be checked to make |
| * sure it points back to this data block. If the check fails, |
| * the data area has been recycled by another writer. |
| */ |
| id = blk->id; /* LMM(data_make_reusable:A) */ |
| |
| d_state = desc_read(desc_ring, id, &desc, |
| NULL, NULL); /* LMM(data_make_reusable:B) */ |
| |
| switch (d_state) { |
| case desc_miss: |
| case desc_reserved: |
| case desc_committed: |
| return false; |
| case desc_finalized: |
| /* |
| * This data block is invalid if the descriptor |
| * does not point back to it. |
| */ |
| if (blk_lpos->begin != lpos_begin) |
| return false; |
| desc_make_reusable(desc_ring, id); |
| break; |
| case desc_reusable: |
| /* |
| * This data block is invalid if the descriptor |
| * does not point back to it. |
| */ |
| if (blk_lpos->begin != lpos_begin) |
| return false; |
| break; |
| } |
| |
| /* Advance @lpos_begin to the next data block. */ |
| lpos_begin = blk_lpos->next; |
| } |
| |
| *lpos_out = lpos_begin; |
| return true; |
| } |
| |
| /* |
| * Advance the data ring tail to at least @lpos. This function puts |
| * descriptors into the reusable state if the tail is pushed beyond |
| * their associated data block. |
| */ |
| static bool data_push_tail(struct printk_ringbuffer *rb, |
| struct prb_data_ring *data_ring, |
| unsigned long lpos) |
| { |
| unsigned long tail_lpos_new; |
| unsigned long tail_lpos; |
| unsigned long next_lpos; |
| |
| /* If @lpos is from a data-less block, there is nothing to do. */ |
| if (LPOS_DATALESS(lpos)) |
| return true; |
| |
| /* |
| * Any descriptor states that have transitioned to reusable due to the |
| * data tail being pushed to this loaded value will be visible to this |
| * CPU. This pairs with data_push_tail:D. |
| * |
| * Memory barrier involvement: |
| * |
| * If data_push_tail:A reads from data_push_tail:D, then this CPU can |
| * see desc_make_reusable:A. |
| * |
| * Relies on: |
| * |
| * MB from desc_make_reusable:A to data_push_tail:D |
| * matches |
| * READFROM from data_push_tail:D to data_push_tail:A |
| * thus |
| * READFROM from desc_make_reusable:A to this CPU |
| */ |
| tail_lpos = atomic_long_read(&data_ring->tail_lpos); /* LMM(data_push_tail:A) */ |
| |
| /* |
| * Loop until the tail lpos is at or beyond @lpos. This condition |
| * may already be satisfied, resulting in no full memory barrier |
| * from data_push_tail:D being performed. However, since this CPU |
| * sees the new tail lpos, any descriptor states that transitioned to |
| * the reusable state must already be visible. |
| */ |
| while ((lpos - tail_lpos) - 1 < DATA_SIZE(data_ring)) { |
| /* |
| * Make all descriptors reusable that are associated with |
| * data blocks before @lpos. |
| */ |
| if (!data_make_reusable(rb, data_ring, tail_lpos, lpos, |
| &next_lpos)) { |
| /* |
| * 1. Guarantee the block ID loaded in |
| * data_make_reusable() is performed before |
| * reloading the tail lpos. The failed |
| * data_make_reusable() may be due to a newly |
| * recycled data area causing the tail lpos to |
| * have been previously pushed. This pairs with |
| * data_alloc:A and data_realloc:A. |
| * |
| * Memory barrier involvement: |
| * |
| * If data_make_reusable:A reads from data_alloc:B, |
| * then data_push_tail:C reads from |
| * data_push_tail:D. |
| * |
| * Relies on: |
| * |
| * MB from data_push_tail:D to data_alloc:B |
| * matching |
| * RMB from data_make_reusable:A to |
| * data_push_tail:C |
| * |
| * Note: data_push_tail:D and data_alloc:B can be |
| * different CPUs. However, the data_alloc:B |
| * CPU (which performs the full memory |
| * barrier) must have previously seen |
| * data_push_tail:D. |
| * |
| * 2. Guarantee the descriptor state loaded in |
| * data_make_reusable() is performed before |
| * reloading the tail lpos. The failed |
| * data_make_reusable() may be due to a newly |
| * recycled descriptor causing the tail lpos to |
| * have been previously pushed. This pairs with |
| * desc_reserve:D. |
| * |
| * Memory barrier involvement: |
| * |
| * If data_make_reusable:B reads from |
| * desc_reserve:F, then data_push_tail:C reads |
| * from data_push_tail:D. |
| * |
| * Relies on: |
| * |
| * MB from data_push_tail:D to desc_reserve:F |
| * matching |
| * RMB from data_make_reusable:B to |
| * data_push_tail:C |
| * |
| * Note: data_push_tail:D and desc_reserve:F can |
| * be different CPUs. However, the |
| * desc_reserve:F CPU (which performs the |
| * full memory barrier) must have previously |
| * seen data_push_tail:D. |
| */ |
| smp_rmb(); /* LMM(data_push_tail:B) */ |
| |
| tail_lpos_new = atomic_long_read(&data_ring->tail_lpos |
| ); /* LMM(data_push_tail:C) */ |
| if (tail_lpos_new == tail_lpos) |
| return false; |
| |
| /* Another CPU pushed the tail. Try again. */ |
| tail_lpos = tail_lpos_new; |
| continue; |
| } |
| |
| /* |
| * Guarantee any descriptor states that have transitioned to |
| * reusable are stored before pushing the tail lpos. A full |
| * memory barrier is needed since other CPUs may have made |
| * the descriptor states reusable. This pairs with |
| * data_push_tail:A. |
| */ |
| if (atomic_long_try_cmpxchg(&data_ring->tail_lpos, &tail_lpos, |
| next_lpos)) { /* LMM(data_push_tail:D) */ |
| break; |
| } |
| } |
| |
| return true; |
| } |
| |
| /* |
| * Advance the desc ring tail. This function advances the tail by one |
| * descriptor, thus invalidating the oldest descriptor. Before advancing |
| * the tail, the tail descriptor is made reusable and all data blocks up to |
| * and including the descriptor's data block are invalidated (i.e. the data |
| * ring tail is pushed past the data block of the descriptor being made |
| * reusable). |
| */ |
| static bool desc_push_tail(struct printk_ringbuffer *rb, |
| unsigned long tail_id) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| enum desc_state d_state; |
| struct prb_desc desc; |
| |
| d_state = desc_read(desc_ring, tail_id, &desc, NULL, NULL); |
| |
| switch (d_state) { |
| case desc_miss: |
| /* |
| * If the ID is exactly 1 wrap behind the expected, it is |
| * in the process of being reserved by another writer and |
| * must be considered reserved. |
| */ |
| if (DESC_ID(atomic_long_read(&desc.state_var)) == |
| DESC_ID_PREV_WRAP(desc_ring, tail_id)) { |
| return false; |
| } |
| |
| /* |
| * The ID has changed. Another writer must have pushed the |
| * tail and recycled the descriptor already. Success is |
| * returned because the caller is only interested in the |
| * specified tail being pushed, which it was. |
| */ |
| return true; |
| case desc_reserved: |
| case desc_committed: |
| return false; |
| case desc_finalized: |
| desc_make_reusable(desc_ring, tail_id); |
| break; |
| case desc_reusable: |
| break; |
| } |
| |
| /* |
| * Data blocks must be invalidated before their associated |
| * descriptor can be made available for recycling. Invalidating |
| * them later is not possible because there is no way to trust |
| * data blocks once their associated descriptor is gone. |
| */ |
| |
| if (!data_push_tail(rb, &rb->text_data_ring, desc.text_blk_lpos.next)) |
| return false; |
| |
| /* |
| * Check the next descriptor after @tail_id before pushing the tail |
| * to it because the tail must always be in a finalized or reusable |
| * state. The implementation of prb_first_seq() relies on this. |
| * |
| * A successful read implies that the next descriptor is less than or |
| * equal to @head_id so there is no risk of pushing the tail past the |
| * head. |
| */ |
| d_state = desc_read(desc_ring, DESC_ID(tail_id + 1), &desc, |
| NULL, NULL); /* LMM(desc_push_tail:A) */ |
| |
| if (d_state == desc_finalized || d_state == desc_reusable) { |
| /* |
| * Guarantee any descriptor states that have transitioned to |
| * reusable are stored before pushing the tail ID. This allows |
| * verifying the recycled descriptor state. A full memory |
| * barrier is needed since other CPUs may have made the |
| * descriptor states reusable. This pairs with desc_reserve:D. |
| */ |
| atomic_long_cmpxchg(&desc_ring->tail_id, tail_id, |
| DESC_ID(tail_id + 1)); /* LMM(desc_push_tail:B) */ |
| } else { |
| /* |
| * Guarantee the last state load from desc_read() is before |
| * reloading @tail_id in order to see a new tail ID in the |
| * case that the descriptor has been recycled. This pairs |
| * with desc_reserve:D. |
| * |
| * Memory barrier involvement: |
| * |
| * If desc_push_tail:A reads from desc_reserve:F, then |
| * desc_push_tail:D reads from desc_push_tail:B. |
| * |
| * Relies on: |
| * |
| * MB from desc_push_tail:B to desc_reserve:F |
| * matching |
| * RMB from desc_push_tail:A to desc_push_tail:D |
| * |
| * Note: desc_push_tail:B and desc_reserve:F can be different |
| * CPUs. However, the desc_reserve:F CPU (which performs |
| * the full memory barrier) must have previously seen |
| * desc_push_tail:B. |
| */ |
| smp_rmb(); /* LMM(desc_push_tail:C) */ |
| |
| /* |
| * Re-check the tail ID. The descriptor following @tail_id is |
| * not in an allowed tail state. But if the tail has since |
| * been moved by another CPU, then it does not matter. |
| */ |
| if (atomic_long_read(&desc_ring->tail_id) == tail_id) /* LMM(desc_push_tail:D) */ |
| return false; |
| } |
| |
| return true; |
| } |
| |
| /* Reserve a new descriptor, invalidating the oldest if necessary. */ |
| static bool desc_reserve(struct printk_ringbuffer *rb, unsigned long *id_out) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| unsigned long prev_state_val; |
| unsigned long id_prev_wrap; |
| struct prb_desc *desc; |
| unsigned long head_id; |
| unsigned long id; |
| |
| head_id = atomic_long_read(&desc_ring->head_id); /* LMM(desc_reserve:A) */ |
| |
| do { |
| desc = to_desc(desc_ring, head_id); |
| |
| id = DESC_ID(head_id + 1); |
| id_prev_wrap = DESC_ID_PREV_WRAP(desc_ring, id); |
| |
| /* |
| * Guarantee the head ID is read before reading the tail ID. |
| * Since the tail ID is updated before the head ID, this |
| * guarantees that @id_prev_wrap is never ahead of the tail |
| * ID. This pairs with desc_reserve:D. |
| * |
| * Memory barrier involvement: |
| * |
| * If desc_reserve:A reads from desc_reserve:D, then |
| * desc_reserve:C reads from desc_push_tail:B. |
| * |
| * Relies on: |
| * |
| * MB from desc_push_tail:B to desc_reserve:D |
| * matching |
| * RMB from desc_reserve:A to desc_reserve:C |
| * |
| * Note: desc_push_tail:B and desc_reserve:D can be different |
| * CPUs. However, the desc_reserve:D CPU (which performs |
| * the full memory barrier) must have previously seen |
| * desc_push_tail:B. |
| */ |
| smp_rmb(); /* LMM(desc_reserve:B) */ |
| |
| if (id_prev_wrap == atomic_long_read(&desc_ring->tail_id |
| )) { /* LMM(desc_reserve:C) */ |
| /* |
| * Make space for the new descriptor by |
| * advancing the tail. |
| */ |
| if (!desc_push_tail(rb, id_prev_wrap)) |
| return false; |
| } |
| |
| /* |
| * 1. Guarantee the tail ID is read before validating the |
| * recycled descriptor state. A read memory barrier is |
| * sufficient for this. This pairs with desc_push_tail:B. |
| * |
| * Memory barrier involvement: |
| * |
| * If desc_reserve:C reads from desc_push_tail:B, then |
| * desc_reserve:E reads from desc_make_reusable:A. |
| * |
| * Relies on: |
| * |
| * MB from desc_make_reusable:A to desc_push_tail:B |
| * matching |
| * RMB from desc_reserve:C to desc_reserve:E |
| * |
| * Note: desc_make_reusable:A and desc_push_tail:B can be |
| * different CPUs. However, the desc_push_tail:B CPU |
| * (which performs the full memory barrier) must have |
| * previously seen desc_make_reusable:A. |
| * |
| * 2. Guarantee the tail ID is stored before storing the head |
| * ID. This pairs with desc_reserve:B. |
| * |
| * 3. Guarantee any data ring tail changes are stored before |
| * recycling the descriptor. Data ring tail changes can |
| * happen via desc_push_tail()->data_push_tail(). A full |
| * memory barrier is needed since another CPU may have |
| * pushed the data ring tails. This pairs with |
| * data_push_tail:B. |
| * |
| * 4. Guarantee a new tail ID is stored before recycling the |
| * descriptor. A full memory barrier is needed since |
| * another CPU may have pushed the tail ID. This pairs |
| * with desc_push_tail:C and this also pairs with |
| * prb_first_seq:C. |
| * |
| * 5. Guarantee the head ID is stored before trying to |
| * finalize the previous descriptor. This pairs with |
| * _prb_commit:B. |
| */ |
| } while (!atomic_long_try_cmpxchg(&desc_ring->head_id, &head_id, |
| id)); /* LMM(desc_reserve:D) */ |
| |
| desc = to_desc(desc_ring, id); |
| |
| /* |
| * If the descriptor has been recycled, verify the old state val. |
| * See "ABA Issues" about why this verification is performed. |
| */ |
| prev_state_val = atomic_long_read(&desc->state_var); /* LMM(desc_reserve:E) */ |
| if (prev_state_val && |
| get_desc_state(id_prev_wrap, prev_state_val) != desc_reusable) { |
| WARN_ON_ONCE(1); |
| return false; |
| } |
| |
| /* |
| * Assign the descriptor a new ID and set its state to reserved. |
| * See "ABA Issues" about why cmpxchg() instead of set() is used. |
| * |
| * Guarantee the new descriptor ID and state is stored before making |
| * any other changes. A write memory barrier is sufficient for this. |
| * This pairs with desc_read:D. |
| */ |
| if (!atomic_long_try_cmpxchg(&desc->state_var, &prev_state_val, |
| DESC_SV(id, desc_reserved))) { /* LMM(desc_reserve:F) */ |
| WARN_ON_ONCE(1); |
| return false; |
| } |
| |
| /* Now data in @desc can be modified: LMM(desc_reserve:G) */ |
| |
| *id_out = id; |
| return true; |
| } |
| |
| /* Determine the end of a data block. */ |
| static unsigned long get_next_lpos(struct prb_data_ring *data_ring, |
| unsigned long lpos, unsigned int size) |
| { |
| unsigned long begin_lpos; |
| unsigned long next_lpos; |
| |
| begin_lpos = lpos; |
| next_lpos = lpos + size; |
| |
| /* First check if the data block does not wrap. */ |
| if (DATA_WRAPS(data_ring, begin_lpos) == DATA_WRAPS(data_ring, next_lpos)) |
| return next_lpos; |
| |
| /* Wrapping data blocks store their data at the beginning. */ |
| return (DATA_THIS_WRAP_START_LPOS(data_ring, next_lpos) + size); |
| } |
| |
| /* |
| * Allocate a new data block, invalidating the oldest data block(s) |
| * if necessary. This function also associates the data block with |
| * a specified descriptor. |
| */ |
| static char *data_alloc(struct printk_ringbuffer *rb, |
| struct prb_data_ring *data_ring, unsigned int size, |
| struct prb_data_blk_lpos *blk_lpos, unsigned long id) |
| { |
| struct prb_data_block *blk; |
| unsigned long begin_lpos; |
| unsigned long next_lpos; |
| |
| if (size == 0) { |
| /* Specify a data-less block. */ |
| blk_lpos->begin = NO_LPOS; |
| blk_lpos->next = NO_LPOS; |
| return NULL; |
| } |
| |
| size = to_blk_size(size); |
| |
| begin_lpos = atomic_long_read(&data_ring->head_lpos); |
| |
| do { |
| next_lpos = get_next_lpos(data_ring, begin_lpos, size); |
| |
| if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring))) { |
| /* Failed to allocate, specify a data-less block. */ |
| blk_lpos->begin = FAILED_LPOS; |
| blk_lpos->next = FAILED_LPOS; |
| return NULL; |
| } |
| |
| /* |
| * 1. Guarantee any descriptor states that have transitioned |
| * to reusable are stored before modifying the newly |
| * allocated data area. A full memory barrier is needed |
| * since other CPUs may have made the descriptor states |
| * reusable. See data_push_tail:A about why the reusable |
| * states are visible. This pairs with desc_read:D. |
| * |
| * 2. Guarantee any updated tail lpos is stored before |
| * modifying the newly allocated data area. Another CPU may |
| * be in data_make_reusable() and is reading a block ID |
| * from this area. data_make_reusable() can handle reading |
| * a garbage block ID value, but then it must be able to |
| * load a new tail lpos. A full memory barrier is needed |
| * since other CPUs may have updated the tail lpos. This |
| * pairs with data_push_tail:B. |
| */ |
| } while (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &begin_lpos, |
| next_lpos)); /* LMM(data_alloc:A) */ |
| |
| blk = to_block(data_ring, begin_lpos); |
| blk->id = id; /* LMM(data_alloc:B) */ |
| |
| if (DATA_WRAPS(data_ring, begin_lpos) != DATA_WRAPS(data_ring, next_lpos)) { |
| /* Wrapping data blocks store their data at the beginning. */ |
| blk = to_block(data_ring, 0); |
| |
| /* |
| * Store the ID on the wrapped block for consistency. |
| * The printk_ringbuffer does not actually use it. |
| */ |
| blk->id = id; |
| } |
| |
| blk_lpos->begin = begin_lpos; |
| blk_lpos->next = next_lpos; |
| |
| return &blk->data[0]; |
| } |
| |
| /* |
| * Try to resize an existing data block associated with the descriptor |
| * specified by @id. If the resized data block should become wrapped, it |
| * copies the old data to the new data block. If @size yields a data block |
| * with the same or less size, the data block is left as is. |
| * |
| * Fail if this is not the last allocated data block or if there is not |
| * enough space or it is not possible make enough space. |
| * |
| * Return a pointer to the beginning of the entire data buffer or NULL on |
| * failure. |
| */ |
| static char *data_realloc(struct printk_ringbuffer *rb, |
| struct prb_data_ring *data_ring, unsigned int size, |
| struct prb_data_blk_lpos *blk_lpos, unsigned long id) |
| { |
| struct prb_data_block *blk; |
| unsigned long head_lpos; |
| unsigned long next_lpos; |
| bool wrapped; |
| |
| /* Reallocation only works if @blk_lpos is the newest data block. */ |
| head_lpos = atomic_long_read(&data_ring->head_lpos); |
| if (head_lpos != blk_lpos->next) |
| return NULL; |
| |
| /* Keep track if @blk_lpos was a wrapping data block. */ |
| wrapped = (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, blk_lpos->next)); |
| |
| size = to_blk_size(size); |
| |
| next_lpos = get_next_lpos(data_ring, blk_lpos->begin, size); |
| |
| /* If the data block does not increase, there is nothing to do. */ |
| if (head_lpos - next_lpos < DATA_SIZE(data_ring)) { |
| if (wrapped) |
| blk = to_block(data_ring, 0); |
| else |
| blk = to_block(data_ring, blk_lpos->begin); |
| return &blk->data[0]; |
| } |
| |
| if (!data_push_tail(rb, data_ring, next_lpos - DATA_SIZE(data_ring))) |
| return NULL; |
| |
| /* The memory barrier involvement is the same as data_alloc:A. */ |
| if (!atomic_long_try_cmpxchg(&data_ring->head_lpos, &head_lpos, |
| next_lpos)) { /* LMM(data_realloc:A) */ |
| return NULL; |
| } |
| |
| blk = to_block(data_ring, blk_lpos->begin); |
| |
| if (DATA_WRAPS(data_ring, blk_lpos->begin) != DATA_WRAPS(data_ring, next_lpos)) { |
| struct prb_data_block *old_blk = blk; |
| |
| /* Wrapping data blocks store their data at the beginning. */ |
| blk = to_block(data_ring, 0); |
| |
| /* |
| * Store the ID on the wrapped block for consistency. |
| * The printk_ringbuffer does not actually use it. |
| */ |
| blk->id = id; |
| |
| if (!wrapped) { |
| /* |
| * Since the allocated space is now in the newly |
| * created wrapping data block, copy the content |
| * from the old data block. |
| */ |
| memcpy(&blk->data[0], &old_blk->data[0], |
| (blk_lpos->next - blk_lpos->begin) - sizeof(blk->id)); |
| } |
| } |
| |
| blk_lpos->next = next_lpos; |
| |
| return &blk->data[0]; |
| } |
| |
| /* Return the number of bytes used by a data block. */ |
| static unsigned int space_used(struct prb_data_ring *data_ring, |
| struct prb_data_blk_lpos *blk_lpos) |
| { |
| /* Data-less blocks take no space. */ |
| if (BLK_DATALESS(blk_lpos)) |
| return 0; |
| |
| if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next)) { |
| /* Data block does not wrap. */ |
| return (DATA_INDEX(data_ring, blk_lpos->next) - |
| DATA_INDEX(data_ring, blk_lpos->begin)); |
| } |
| |
| /* |
| * For wrapping data blocks, the trailing (wasted) space is |
| * also counted. |
| */ |
| return (DATA_INDEX(data_ring, blk_lpos->next) + |
| DATA_SIZE(data_ring) - DATA_INDEX(data_ring, blk_lpos->begin)); |
| } |
| |
| /* |
| * Given @blk_lpos, return a pointer to the writer data from the data block |
| * and calculate the size of the data part. A NULL pointer is returned if |
| * @blk_lpos specifies values that could never be legal. |
| * |
| * This function (used by readers) performs strict validation on the lpos |
| * values to possibly detect bugs in the writer code. A WARN_ON_ONCE() is |
| * triggered if an internal error is detected. |
| */ |
| static const char *get_data(struct prb_data_ring *data_ring, |
| struct prb_data_blk_lpos *blk_lpos, |
| unsigned int *data_size) |
| { |
| struct prb_data_block *db; |
| |
| /* Data-less data block description. */ |
| if (BLK_DATALESS(blk_lpos)) { |
| if (blk_lpos->begin == NO_LPOS && blk_lpos->next == NO_LPOS) { |
| *data_size = 0; |
| return ""; |
| } |
| return NULL; |
| } |
| |
| /* Regular data block: @begin less than @next and in same wrap. */ |
| if (DATA_WRAPS(data_ring, blk_lpos->begin) == DATA_WRAPS(data_ring, blk_lpos->next) && |
| blk_lpos->begin < blk_lpos->next) { |
| db = to_block(data_ring, blk_lpos->begin); |
| *data_size = blk_lpos->next - blk_lpos->begin; |
| |
| /* Wrapping data block: @begin is one wrap behind @next. */ |
| } else if (DATA_WRAPS(data_ring, blk_lpos->begin + DATA_SIZE(data_ring)) == |
| DATA_WRAPS(data_ring, blk_lpos->next)) { |
| db = to_block(data_ring, 0); |
| *data_size = DATA_INDEX(data_ring, blk_lpos->next); |
| |
| /* Illegal block description. */ |
| } else { |
| WARN_ON_ONCE(1); |
| return NULL; |
| } |
| |
| /* A valid data block will always be aligned to the ID size. */ |
| if (WARN_ON_ONCE(blk_lpos->begin != ALIGN(blk_lpos->begin, sizeof(db->id))) || |
| WARN_ON_ONCE(blk_lpos->next != ALIGN(blk_lpos->next, sizeof(db->id)))) { |
| return NULL; |
| } |
| |
| /* A valid data block will always have at least an ID. */ |
| if (WARN_ON_ONCE(*data_size < sizeof(db->id))) |
| return NULL; |
| |
| /* Subtract block ID space from size to reflect data size. */ |
| *data_size -= sizeof(db->id); |
| |
| return &db->data[0]; |
| } |
| |
| /* |
| * Attempt to transition the newest descriptor from committed back to reserved |
| * so that the record can be modified by a writer again. This is only possible |
| * if the descriptor is not yet finalized and the provided @caller_id matches. |
| */ |
| static struct prb_desc *desc_reopen_last(struct prb_desc_ring *desc_ring, |
| u32 caller_id, unsigned long *id_out) |
| { |
| unsigned long prev_state_val; |
| enum desc_state d_state; |
| struct prb_desc desc; |
| struct prb_desc *d; |
| unsigned long id; |
| u32 cid; |
| |
| id = atomic_long_read(&desc_ring->head_id); |
| |
| /* |
| * To reduce unnecessarily reopening, first check if the descriptor |
| * state and caller ID are correct. |
| */ |
| d_state = desc_read(desc_ring, id, &desc, NULL, &cid); |
| if (d_state != desc_committed || cid != caller_id) |
| return NULL; |
| |
| d = to_desc(desc_ring, id); |
| |
| prev_state_val = DESC_SV(id, desc_committed); |
| |
| /* |
| * Guarantee the reserved state is stored before reading any |
| * record data. A full memory barrier is needed because @state_var |
| * modification is followed by reading. This pairs with _prb_commit:B. |
| * |
| * Memory barrier involvement: |
| * |
| * If desc_reopen_last:A reads from _prb_commit:B, then |
| * prb_reserve_in_last:A reads from _prb_commit:A. |
| * |
| * Relies on: |
| * |
| * WMB from _prb_commit:A to _prb_commit:B |
| * matching |
| * MB If desc_reopen_last:A to prb_reserve_in_last:A |
| */ |
| if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val, |
| DESC_SV(id, desc_reserved))) { /* LMM(desc_reopen_last:A) */ |
| return NULL; |
| } |
| |
| *id_out = id; |
| return d; |
| } |
| |
| /** |
| * prb_reserve_in_last() - Re-reserve and extend the space in the ringbuffer |
| * used by the newest record. |
| * |
| * @e: The entry structure to setup. |
| * @rb: The ringbuffer to re-reserve and extend data in. |
| * @r: The record structure to allocate buffers for. |
| * @caller_id: The caller ID of the caller (reserving writer). |
| * @max_size: Fail if the extended size would be greater than this. |
| * |
| * This is the public function available to writers to re-reserve and extend |
| * data. |
| * |
| * The writer specifies the text size to extend (not the new total size) by |
| * setting the @text_buf_size field of @r. To ensure proper initialization |
| * of @r, prb_rec_init_wr() should be used. |
| * |
| * This function will fail if @caller_id does not match the caller ID of the |
| * newest record. In that case the caller must reserve new data using |
| * prb_reserve(). |
| * |
| * Context: Any context. Disables local interrupts on success. |
| * Return: true if text data could be extended, otherwise false. |
| * |
| * On success: |
| * |
| * - @r->text_buf points to the beginning of the entire text buffer. |
| * |
| * - @r->text_buf_size is set to the new total size of the buffer. |
| * |
| * - @r->info is not touched so that @r->info->text_len could be used |
| * to append the text. |
| * |
| * - prb_record_text_space() can be used on @e to query the new |
| * actually used space. |
| * |
| * Important: All @r->info fields will already be set with the current values |
| * for the record. I.e. @r->info->text_len will be less than |
| * @text_buf_size. Writers can use @r->info->text_len to know |
| * where concatenation begins and writers should update |
| * @r->info->text_len after concatenating. |
| */ |
| bool prb_reserve_in_last(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, |
| struct printk_record *r, u32 caller_id, unsigned int max_size) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| struct printk_info *info; |
| unsigned int data_size; |
| struct prb_desc *d; |
| unsigned long id; |
| |
| local_irq_save(e->irqflags); |
| |
| /* Transition the newest descriptor back to the reserved state. */ |
| d = desc_reopen_last(desc_ring, caller_id, &id); |
| if (!d) { |
| local_irq_restore(e->irqflags); |
| goto fail_reopen; |
| } |
| |
| /* Now the writer has exclusive access: LMM(prb_reserve_in_last:A) */ |
| |
| info = to_info(desc_ring, id); |
| |
| /* |
| * Set the @e fields here so that prb_commit() can be used if |
| * anything fails from now on. |
| */ |
| e->rb = rb; |
| e->id = id; |
| |
| /* |
| * desc_reopen_last() checked the caller_id, but there was no |
| * exclusive access at that point. The descriptor may have |
| * changed since then. |
| */ |
| if (caller_id != info->caller_id) |
| goto fail; |
| |
| if (BLK_DATALESS(&d->text_blk_lpos)) { |
| if (WARN_ON_ONCE(info->text_len != 0)) { |
| pr_warn_once("wrong text_len value (%hu, expecting 0)\n", |
| info->text_len); |
| info->text_len = 0; |
| } |
| |
| if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) |
| goto fail; |
| |
| if (r->text_buf_size > max_size) |
| goto fail; |
| |
| r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size, |
| &d->text_blk_lpos, id); |
| } else { |
| if (!get_data(&rb->text_data_ring, &d->text_blk_lpos, &data_size)) |
| goto fail; |
| |
| /* |
| * Increase the buffer size to include the original size. If |
| * the meta data (@text_len) is not sane, use the full data |
| * block size. |
| */ |
| if (WARN_ON_ONCE(info->text_len > data_size)) { |
| pr_warn_once("wrong text_len value (%hu, expecting <=%u)\n", |
| info->text_len, data_size); |
| info->text_len = data_size; |
| } |
| r->text_buf_size += info->text_len; |
| |
| if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) |
| goto fail; |
| |
| if (r->text_buf_size > max_size) |
| goto fail; |
| |
| r->text_buf = data_realloc(rb, &rb->text_data_ring, r->text_buf_size, |
| &d->text_blk_lpos, id); |
| } |
| if (r->text_buf_size && !r->text_buf) |
| goto fail; |
| |
| r->info = info; |
| |
| e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos); |
| |
| return true; |
| fail: |
| prb_commit(e); |
| /* prb_commit() re-enabled interrupts. */ |
| fail_reopen: |
| /* Make it clear to the caller that the re-reserve failed. */ |
| memset(r, 0, sizeof(*r)); |
| return false; |
| } |
| |
| /* |
| * Attempt to finalize a specified descriptor. If this fails, the descriptor |
| * is either already final or it will finalize itself when the writer commits. |
| */ |
| static void desc_make_final(struct prb_desc_ring *desc_ring, unsigned long id) |
| { |
| unsigned long prev_state_val = DESC_SV(id, desc_committed); |
| struct prb_desc *d = to_desc(desc_ring, id); |
| |
| atomic_long_cmpxchg_relaxed(&d->state_var, prev_state_val, |
| DESC_SV(id, desc_finalized)); /* LMM(desc_make_final:A) */ |
| } |
| |
| /** |
| * prb_reserve() - Reserve space in the ringbuffer. |
| * |
| * @e: The entry structure to setup. |
| * @rb: The ringbuffer to reserve data in. |
| * @r: The record structure to allocate buffers for. |
| * |
| * This is the public function available to writers to reserve data. |
| * |
| * The writer specifies the text size to reserve by setting the |
| * @text_buf_size field of @r. To ensure proper initialization of @r, |
| * prb_rec_init_wr() should be used. |
| * |
| * Context: Any context. Disables local interrupts on success. |
| * Return: true if at least text data could be allocated, otherwise false. |
| * |
| * On success, the fields @info and @text_buf of @r will be set by this |
| * function and should be filled in by the writer before committing. Also |
| * on success, prb_record_text_space() can be used on @e to query the actual |
| * space used for the text data block. |
| * |
| * Important: @info->text_len needs to be set correctly by the writer in |
| * order for data to be readable and/or extended. Its value |
| * is initialized to 0. |
| */ |
| bool prb_reserve(struct prb_reserved_entry *e, struct printk_ringbuffer *rb, |
| struct printk_record *r) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| struct printk_info *info; |
| struct prb_desc *d; |
| unsigned long id; |
| u64 seq; |
| |
| if (!data_check_size(&rb->text_data_ring, r->text_buf_size)) |
| goto fail; |
| |
| /* |
| * Descriptors in the reserved state act as blockers to all further |
| * reservations once the desc_ring has fully wrapped. Disable |
| * interrupts during the reserve/commit window in order to minimize |
| * the likelihood of this happening. |
| */ |
| local_irq_save(e->irqflags); |
| |
| if (!desc_reserve(rb, &id)) { |
| /* Descriptor reservation failures are tracked. */ |
| atomic_long_inc(&rb->fail); |
| local_irq_restore(e->irqflags); |
| goto fail; |
| } |
| |
| d = to_desc(desc_ring, id); |
| info = to_info(desc_ring, id); |
| |
| /* |
| * All @info fields (except @seq) are cleared and must be filled in |
| * by the writer. Save @seq before clearing because it is used to |
| * determine the new sequence number. |
| */ |
| seq = info->seq; |
| memset(info, 0, sizeof(*info)); |
| |
| /* |
| * Set the @e fields here so that prb_commit() can be used if |
| * text data allocation fails. |
| */ |
| e->rb = rb; |
| e->id = id; |
| |
| /* |
| * Initialize the sequence number if it has "never been set". |
| * Otherwise just increment it by a full wrap. |
| * |
| * @seq is considered "never been set" if it has a value of 0, |
| * _except_ for @infos[0], which was specially setup by the ringbuffer |
| * initializer and therefore is always considered as set. |
| * |
| * See the "Bootstrap" comment block in printk_ringbuffer.h for |
| * details about how the initializer bootstraps the descriptors. |
| */ |
| if (seq == 0 && DESC_INDEX(desc_ring, id) != 0) |
| info->seq = DESC_INDEX(desc_ring, id); |
| else |
| info->seq = seq + DESCS_COUNT(desc_ring); |
| |
| /* |
| * New data is about to be reserved. Once that happens, previous |
| * descriptors are no longer able to be extended. Finalize the |
| * previous descriptor now so that it can be made available to |
| * readers. (For seq==0 there is no previous descriptor.) |
| */ |
| if (info->seq > 0) |
| desc_make_final(desc_ring, DESC_ID(id - 1)); |
| |
| r->text_buf = data_alloc(rb, &rb->text_data_ring, r->text_buf_size, |
| &d->text_blk_lpos, id); |
| /* If text data allocation fails, a data-less record is committed. */ |
| if (r->text_buf_size && !r->text_buf) { |
| prb_commit(e); |
| /* prb_commit() re-enabled interrupts. */ |
| goto fail; |
| } |
| |
| r->info = info; |
| |
| /* Record full text space used by record. */ |
| e->text_space = space_used(&rb->text_data_ring, &d->text_blk_lpos); |
| |
| return true; |
| fail: |
| /* Make it clear to the caller that the reserve failed. */ |
| memset(r, 0, sizeof(*r)); |
| return false; |
| } |
| |
| /* Commit the data (possibly finalizing it) and restore interrupts. */ |
| static void _prb_commit(struct prb_reserved_entry *e, unsigned long state_val) |
| { |
| struct prb_desc_ring *desc_ring = &e->rb->desc_ring; |
| struct prb_desc *d = to_desc(desc_ring, e->id); |
| unsigned long prev_state_val = DESC_SV(e->id, desc_reserved); |
| |
| /* Now the writer has finished all writing: LMM(_prb_commit:A) */ |
| |
| /* |
| * Set the descriptor as committed. See "ABA Issues" about why |
| * cmpxchg() instead of set() is used. |
| * |
| * 1 Guarantee all record data is stored before the descriptor state |
| * is stored as committed. A write memory barrier is sufficient |
| * for this. This pairs with desc_read:B and desc_reopen_last:A. |
| * |
| * 2. Guarantee the descriptor state is stored as committed before |
| * re-checking the head ID in order to possibly finalize this |
| * descriptor. This pairs with desc_reserve:D. |
| * |
| * Memory barrier involvement: |
| * |
| * If prb_commit:A reads from desc_reserve:D, then |
| * desc_make_final:A reads from _prb_commit:B. |
| * |
| * Relies on: |
| * |
| * MB _prb_commit:B to prb_commit:A |
| * matching |
| * MB desc_reserve:D to desc_make_final:A |
| */ |
| if (!atomic_long_try_cmpxchg(&d->state_var, &prev_state_val, |
| DESC_SV(e->id, state_val))) { /* LMM(_prb_commit:B) */ |
| WARN_ON_ONCE(1); |
| } |
| |
| /* Restore interrupts, the reserve/commit window is finished. */ |
| local_irq_restore(e->irqflags); |
| } |
| |
| /** |
| * prb_commit() - Commit (previously reserved) data to the ringbuffer. |
| * |
| * @e: The entry containing the reserved data information. |
| * |
| * This is the public function available to writers to commit data. |
| * |
| * Note that the data is not yet available to readers until it is finalized. |
| * Finalizing happens automatically when space for the next record is |
| * reserved. |
| * |
| * See prb_final_commit() for a version of this function that finalizes |
| * immediately. |
| * |
| * Context: Any context. Enables local interrupts. |
| */ |
| void prb_commit(struct prb_reserved_entry *e) |
| { |
| struct prb_desc_ring *desc_ring = &e->rb->desc_ring; |
| unsigned long head_id; |
| |
| _prb_commit(e, desc_committed); |
| |
| /* |
| * If this descriptor is no longer the head (i.e. a new record has |
| * been allocated), extending the data for this record is no longer |
| * allowed and therefore it must be finalized. |
| */ |
| head_id = atomic_long_read(&desc_ring->head_id); /* LMM(prb_commit:A) */ |
| if (head_id != e->id) |
| desc_make_final(desc_ring, e->id); |
| } |
| |
| /** |
| * prb_final_commit() - Commit and finalize (previously reserved) data to |
| * the ringbuffer. |
| * |
| * @e: The entry containing the reserved data information. |
| * |
| * This is the public function available to writers to commit+finalize data. |
| * |
| * By finalizing, the data is made immediately available to readers. |
| * |
| * This function should only be used if there are no intentions of extending |
| * this data using prb_reserve_in_last(). |
| * |
| * Context: Any context. Enables local interrupts. |
| */ |
| void prb_final_commit(struct prb_reserved_entry *e) |
| { |
| _prb_commit(e, desc_finalized); |
| } |
| |
| /* |
| * Count the number of lines in provided text. All text has at least 1 line |
| * (even if @text_size is 0). Each '\n' processed is counted as an additional |
| * line. |
| */ |
| static unsigned int count_lines(const char *text, unsigned int text_size) |
| { |
| unsigned int next_size = text_size; |
| unsigned int line_count = 1; |
| const char *next = text; |
| |
| while (next_size) { |
| next = memchr(next, '\n', next_size); |
| if (!next) |
| break; |
| line_count++; |
| next++; |
| next_size = text_size - (next - text); |
| } |
| |
| return line_count; |
| } |
| |
| /* |
| * Given @blk_lpos, copy an expected @len of data into the provided buffer. |
| * If @line_count is provided, count the number of lines in the data. |
| * |
| * This function (used by readers) performs strict validation on the data |
| * size to possibly detect bugs in the writer code. A WARN_ON_ONCE() is |
| * triggered if an internal error is detected. |
| */ |
| static bool copy_data(struct prb_data_ring *data_ring, |
| struct prb_data_blk_lpos *blk_lpos, u16 len, char *buf, |
| unsigned int buf_size, unsigned int *line_count) |
| { |
| unsigned int data_size; |
| const char *data; |
| |
| /* Caller might not want any data. */ |
| if ((!buf || !buf_size) && !line_count) |
| return true; |
| |
| data = get_data(data_ring, blk_lpos, &data_size); |
| if (!data) |
| return false; |
| |
| /* |
| * Actual cannot be less than expected. It can be more than expected |
| * because of the trailing alignment padding. |
| * |
| * Note that invalid @len values can occur because the caller loads |
| * the value during an allowed data race. |
| */ |
| if (data_size < (unsigned int)len) |
| return false; |
| |
| /* Caller interested in the line count? */ |
| if (line_count) |
| *line_count = count_lines(data, data_size); |
| |
| /* Caller interested in the data content? */ |
| if (!buf || !buf_size) |
| return true; |
| |
| data_size = min_t(u16, buf_size, len); |
| |
| memcpy(&buf[0], data, data_size); /* LMM(copy_data:A) */ |
| return true; |
| } |
| |
| /* |
| * This is an extended version of desc_read(). It gets a copy of a specified |
| * descriptor. However, it also verifies that the record is finalized and has |
| * the sequence number @seq. On success, 0 is returned. |
| * |
| * Error return values: |
| * -EINVAL: A finalized record with sequence number @seq does not exist. |
| * -ENOENT: A finalized record with sequence number @seq exists, but its data |
| * is not available. This is a valid record, so readers should |
| * continue with the next record. |
| */ |
| static int desc_read_finalized_seq(struct prb_desc_ring *desc_ring, |
| unsigned long id, u64 seq, |
| struct prb_desc *desc_out) |
| { |
| struct prb_data_blk_lpos *blk_lpos = &desc_out->text_blk_lpos; |
| enum desc_state d_state; |
| u64 s; |
| |
| d_state = desc_read(desc_ring, id, desc_out, &s, NULL); |
| |
| /* |
| * An unexpected @id (desc_miss) or @seq mismatch means the record |
| * does not exist. A descriptor in the reserved or committed state |
| * means the record does not yet exist for the reader. |
| */ |
| if (d_state == desc_miss || |
| d_state == desc_reserved || |
| d_state == desc_committed || |
| s != seq) { |
| return -EINVAL; |
| } |
| |
| /* |
| * A descriptor in the reusable state may no longer have its data |
| * available; report it as existing but with lost data. Or the record |
| * may actually be a record with lost data. |
| */ |
| if (d_state == desc_reusable || |
| (blk_lpos->begin == FAILED_LPOS && blk_lpos->next == FAILED_LPOS)) { |
| return -ENOENT; |
| } |
| |
| return 0; |
| } |
| |
| /* |
| * Copy the ringbuffer data from the record with @seq to the provided |
| * @r buffer. On success, 0 is returned. |
| * |
| * See desc_read_finalized_seq() for error return values. |
| */ |
| static int prb_read(struct printk_ringbuffer *rb, u64 seq, |
| struct printk_record *r, unsigned int *line_count) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| struct printk_info *info = to_info(desc_ring, seq); |
| struct prb_desc *rdesc = to_desc(desc_ring, seq); |
| atomic_long_t *state_var = &rdesc->state_var; |
| struct prb_desc desc; |
| unsigned long id; |
| int err; |
| |
| /* Extract the ID, used to specify the descriptor to read. */ |
| id = DESC_ID(atomic_long_read(state_var)); |
| |
| /* Get a local copy of the correct descriptor (if available). */ |
| err = desc_read_finalized_seq(desc_ring, id, seq, &desc); |
| |
| /* |
| * If @r is NULL, the caller is only interested in the availability |
| * of the record. |
| */ |
| if (err || !r) |
| return err; |
| |
| /* If requested, copy meta data. */ |
| if (r->info) |
| memcpy(r->info, info, sizeof(*(r->info))); |
| |
| /* Copy text data. If it fails, this is a data-less record. */ |
| if (!copy_data(&rb->text_data_ring, &desc.text_blk_lpos, info->text_len, |
| r->text_buf, r->text_buf_size, line_count)) { |
| return -ENOENT; |
| } |
| |
| /* Ensure the record is still finalized and has the same @seq. */ |
| return desc_read_finalized_seq(desc_ring, id, seq, &desc); |
| } |
| |
| /* Get the sequence number of the tail descriptor. */ |
| static u64 prb_first_seq(struct printk_ringbuffer *rb) |
| { |
| struct prb_desc_ring *desc_ring = &rb->desc_ring; |
| enum desc_state d_state; |
| struct prb_desc desc; |
| unsigned long id; |
| u64 seq; |
| |
| for (;;) { |
| id = atomic_long_read(&rb->desc_ring.tail_id); /* LMM(prb_first_seq:A) */ |
| |
| d_state = desc_read(desc_ring, id, &desc, &seq, NULL); /* LMM(prb_first_seq:B) */ |
| |
| /* |
| * This loop will not be infinite because the tail is |
| * _always_ in the finalized or reusable state. |
| */ |
| if (d_state == desc_finalized || d_state == desc_reusable) |
| break; |
| |
| /* |
| * Guarantee the last state load from desc_read() is before |
| * reloading @tail_id in order to see a new tail in the case |
| * that the descriptor has been recycled. This pairs with |
| * desc_reserve:D. |
| * |
| * Memory barrier involvement: |
| * |
| * If prb_first_seq:B reads from desc_reserve:F, then |
| * prb_first_seq:A reads from desc_push_tail:B. |
| * |
| * Relies on: |
| * |
| * MB from desc_push_tail:B to desc_reserve:F |
| * matching |
| * RMB prb_first_seq:B to prb_first_seq:A |
| */ |
| smp_rmb(); /* LMM(prb_first_seq:C) */ |
| } |
| |
| return seq; |
| } |
| |
| /* |
| * Non-blocking read of a record. Updates @seq to the last finalized record |
| * (which may have no data available). |
| * |
| * See the description of prb_read_valid() and prb_read_valid_info() |
| * for details. |
| */ |
| static bool _prb_read_valid(struct printk_ringbuffer *rb, u64 *seq, |
| struct printk_record *r, unsigned int *line_count) |
| { |
| u64 tail_seq; |
| int err; |
| |
| while ((err = prb_read(rb, *seq, r, line_count))) { |
| tail_seq = prb_first_seq(rb); |
| |
| if (*seq < tail_seq) { |
| /* |
| * Behind the tail. Catch up and try again. This |
| * can happen for -ENOENT and -EINVAL cases. |
| */ |
| *seq = tail_seq; |
| |
| } else if (err == -ENOENT) { |
| /* Record exists, but no data available. Skip. */ |
| (*seq)++; |
| |
| } else { |
| /* Non-existent/non-finalized record. Must stop. */ |
| return false; |
| } |
| } |
| |
| return true; |
| } |
| |
| /** |
| * prb_read_valid() - Non-blocking read of a requested record or (if gone) |
| * the next available record. |
| * |
| * @rb: The ringbuffer to read from. |
| * @seq: The sequence number of the record to read. |
| * @r: A record data buffer to store the read record to. |
| * |
| * This is the public function available to readers to read a record. |
| * |
| * The reader provides the @info and @text_buf buffers of @r to be |
| * filled in. Any of the buffer pointers can be set to NULL if the reader |
| * is not interested in that data. To ensure proper initialization of @r, |
| * prb_rec_init_rd() should be used. |
| * |
| * Context: Any context. |
| * Return: true if a record was read, otherwise false. |
| * |
| * On success, the reader must check r->info.seq to see which record was |
| * actually read. This allows the reader to detect dropped records. |
| * |
| * Failure means @seq refers to a not yet written record. |
| */ |
| bool prb_read_valid(struct printk_ringbuffer *rb, u64 seq, |
| struct printk_record *r) |
| { |
| return _prb_read_valid(rb, &seq, r, NULL); |
| } |
| |
| /** |
| * prb_read_valid_info() - Non-blocking read of meta data for a requested |
| * record or (if gone) the next available record. |
| * |
| * @rb: The ringbuffer to read from. |
| * @seq: The sequence number of the record to read. |
| * @info: A buffer to store the read record meta data to. |
| * @line_count: A buffer to store the number of lines in the record text. |
| * |
| * This is the public function available to readers to read only the |
| * meta data of a record. |
| * |
| * The reader provides the @info, @line_count buffers to be filled in. |
| * Either of the buffer pointers can be set to NULL if the reader is not |
| * interested in that data. |
| * |
| * Context: Any context. |
| * Return: true if a record's meta data was read, otherwise false. |
| * |
| * On success, the reader must check info->seq to see which record meta data |
| * was actually read. This allows the reader to detect dropped records. |
| * |
| * Failure means @seq refers to a not yet written record. |
| */ |
| bool prb_read_valid_info(struct printk_ringbuffer *rb, u64 seq, |
| struct printk_info *info, unsigned int *line_count) |
| { |
| struct printk_record r; |
| |
| prb_rec_init_rd(&r, info, NULL, 0); |
| |
| return _prb_read_valid(rb, &seq, &r, line_count); |
| } |
| |
| /** |
| * prb_first_valid_seq() - Get the sequence number of the oldest available |
| * record. |
| * |
| * @rb: The ringbuffer to get the sequence number from. |
| * |
| * This is the public function available to readers to see what the |
| * first/oldest valid sequence number is. |
| * |
| * This provides readers a starting point to begin iterating the ringbuffer. |
| * |
| * Context: Any context. |
| * Return: The sequence number of the first/oldest record or, if the |
| * ringbuffer is empty, 0 is returned. |
| */ |
| u64 prb_first_valid_seq(struct printk_ringbuffer *rb) |
| { |
| u64 seq = 0; |
| |
| if (!_prb_read_valid(rb, &seq, NULL, NULL)) |
| return 0; |
| |
| return seq; |
| } |
| |
| /** |
| * prb_next_seq() - Get the sequence number after the last available record. |
| * |
| * @rb: The ringbuffer to get the sequence number from. |
| * |
| * This is the public function available to readers to see what the next |
| * newest sequence number available to readers will be. |
| * |
| * This provides readers a sequence number to jump to if all currently |
| * available records should be skipped. |
| * |
| * Context: Any context. |
| * Return: The sequence number of the next newest (not yet available) record |
| * for readers. |
| */ |
| u64 prb_next_seq(struct printk_ringbuffer *rb) |
| { |
| u64 seq = 0; |
| |
| /* Search forward from the oldest descriptor. */ |
| while (_prb_read_valid(rb, &seq, NULL, NULL)) |
| seq++; |
| |
| return seq; |
| } |
| |
| /** |
| * prb_init() - Initialize a ringbuffer to use provided external buffers. |
| * |
| * @rb: The ringbuffer to initialize. |
| * @text_buf: The data buffer for text data. |
| * @textbits: The size of @text_buf as a power-of-2 value. |
| * @descs: The descriptor buffer for ringbuffer records. |
| * @descbits: The count of @descs items as a power-of-2 value. |
| * @infos: The printk_info buffer for ringbuffer records. |
| * |
| * This is the public function available to writers to setup a ringbuffer |
| * during runtime using provided buffers. |
| * |
| * This must match the initialization of DEFINE_PRINTKRB(). |
| * |
| * Context: Any context. |
| */ |
| void prb_init(struct printk_ringbuffer *rb, |
| char *text_buf, unsigned int textbits, |
| struct prb_desc *descs, unsigned int descbits, |
| struct printk_info *infos) |
| { |
| memset(descs, 0, _DESCS_COUNT(descbits) * sizeof(descs[0])); |
| memset(infos, 0, _DESCS_COUNT(descbits) * sizeof(infos[0])); |
| |
| rb->desc_ring.count_bits = descbits; |
| rb->desc_ring.descs = descs; |
| rb->desc_ring.infos = infos; |
| atomic_long_set(&rb->desc_ring.head_id, DESC0_ID(descbits)); |
| atomic_long_set(&rb->desc_ring.tail_id, DESC0_ID(descbits)); |
| |
| rb->text_data_ring.size_bits = textbits; |
| rb->text_data_ring.data = text_buf; |
| atomic_long_set(&rb->text_data_ring.head_lpos, BLK0_LPOS(textbits)); |
| atomic_long_set(&rb->text_data_ring.tail_lpos, BLK0_LPOS(textbits)); |
| |
| atomic_long_set(&rb->fail, 0); |
| |
| atomic_long_set(&(descs[_DESCS_COUNT(descbits) - 1].state_var), DESC0_SV(descbits)); |
| descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.begin = FAILED_LPOS; |
| descs[_DESCS_COUNT(descbits) - 1].text_blk_lpos.next = FAILED_LPOS; |
| |
| infos[0].seq = -(u64)_DESCS_COUNT(descbits); |
| infos[_DESCS_COUNT(descbits) - 1].seq = 0; |
| } |
| |
| /** |
| * prb_record_text_space() - Query the full actual used ringbuffer space for |
| * the text data of a reserved entry. |
| * |
| * @e: The successfully reserved entry to query. |
| * |
| * This is the public function available to writers to see how much actual |
| * space is used in the ringbuffer to store the text data of the specified |
| * entry. |
| * |
| * This function is only valid if @e has been successfully reserved using |
| * prb_reserve(). |
| * |
| * Context: Any context. |
| * Return: The size in bytes used by the text data of the associated record. |
| */ |
| unsigned int prb_record_text_space(struct prb_reserved_entry *e) |
| { |
| return e->text_space; |
| } |