Btrfs: read device stats on mount, write modified ones during commit
The device statistics are written into the device tree with each
transaction commit. Only modified statistics are written.
When a filesystem is mounted, the device statistics for each involved
device are read from the device tree and used to initialize the
counters.
Signed-off-by: Stefan Behrens <sbehrens@giantdisaster.de>
diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index aad2600..e176f8c 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -823,6 +823,14 @@
u8 csum;
} __attribute__ ((__packed__));
+struct btrfs_dev_stats_item {
+ /*
+ * grow this item struct at the end for future enhancements and keep
+ * the existing values unchanged
+ */
+ __le64 values[BTRFS_DEV_STAT_VALUES_MAX];
+} __attribute__ ((__packed__));
+
/* different types of block groups (and chunks) */
#define BTRFS_BLOCK_GROUP_DATA (1ULL << 0)
#define BTRFS_BLOCK_GROUP_SYSTEM (1ULL << 1)
@@ -1508,6 +1516,12 @@
#define BTRFS_BALANCE_ITEM_KEY 248
/*
+ * Persistantly stores the io stats in the device tree.
+ * One key for all stats, (0, BTRFS_DEV_STATS_KEY, devid).
+ */
+#define BTRFS_DEV_STATS_KEY 249
+
+/*
* string items are for debugging. They just store a short string of
* data in the FS
*/
@@ -2415,6 +2429,30 @@
return btrfs_item_size(eb, e) - offset;
}
+/* btrfs_dev_stats_item */
+static inline u64 btrfs_dev_stats_value(struct extent_buffer *eb,
+ struct btrfs_dev_stats_item *ptr,
+ int index)
+{
+ u64 val;
+
+ read_extent_buffer(eb, &val,
+ offsetof(struct btrfs_dev_stats_item, values) +
+ ((unsigned long)ptr) + (index * sizeof(u64)),
+ sizeof(val));
+ return val;
+}
+
+static inline void btrfs_set_dev_stats_value(struct extent_buffer *eb,
+ struct btrfs_dev_stats_item *ptr,
+ int index, u64 val)
+{
+ write_extent_buffer(eb, &val,
+ offsetof(struct btrfs_dev_stats_item, values) +
+ ((unsigned long)ptr) + (index * sizeof(u64)),
+ sizeof(val));
+}
+
static inline struct btrfs_fs_info *btrfs_sb(struct super_block *sb)
{
return sb->s_fs_info;
