fs/erofs/xattr.c - linux - Git at Google

 // SPDX-License-Identifier: GPL-2.0-only
 /*
  * Copyright (C) 2017-2018 HUAWEI, Inc.
  *             https://www.huawei.com/
  */
 #include <linux/security.h>
 #include "xattr.h"

 struct xattr_iter {
 	struct super_block *sb;
 	struct page *page;
 	void *kaddr;

 	erofs_blk_t blkaddr;
 	unsigned int ofs;
 };

 static inline void xattr_iter_end(struct xattr_iter *it, bool atomic)
 {
 	/* the only user of kunmap() is 'init_inode_xattrs' */
 	if (!atomic)
 		kunmap(it->page);
 	else
 		kunmap_atomic(it->kaddr);

 	unlock_page(it->page);
 	put_page(it->page);
 }

 static inline void xattr_iter_end_final(struct xattr_iter *it)
 {
 	if (!it->page)
 		return;

 	xattr_iter_end(it, true);
 }

 static int init_inode_xattrs(struct inode *inode)
 {
 	struct erofs_inode *const vi = EROFS_I(inode);
 	struct xattr_iter it;
 	unsigned int i;
 	struct erofs_xattr_ibody_header *ih;
 	struct super_block *sb;
 	struct erofs_sb_info *sbi;
 	bool atomic_map;
 	int ret = 0;

 	/* the most case is that xattrs of this inode are initialized. */
 	if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags)) {
 		/*
 		 * paired with smp_mb() at the end of the function to ensure
 		 * fields will only be observed after the bit is set.
 		 */
 		smp_mb();
 		return 0;
 	}

 	if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_XATTR_BIT, TASK_KILLABLE))
 		return -ERESTARTSYS;

 	/* someone has initialized xattrs for us? */
 	if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags))
 		goto out_unlock;

 	/*
 	 * bypass all xattr operations if ->xattr_isize is not greater than
 	 * sizeof(struct erofs_xattr_ibody_header), in detail:
 	 * 1) it is not enough to contain erofs_xattr_ibody_header then
 	 *    ->xattr_isize should be 0 (it means no xattr);
 	 * 2) it is just to contain erofs_xattr_ibody_header, which is on-disk
 	 *    undefined right now (maybe use later with some new sb feature).
 	 */
 	if (vi->xattr_isize == sizeof(struct erofs_xattr_ibody_header)) {
 		erofs_err(inode->i_sb,
 			  "xattr_isize %d of nid %llu is not supported yet",
 			  vi->xattr_isize, vi->nid);
 		ret = -EOPNOTSUPP;
 		goto out_unlock;
 	} else if (vi->xattr_isize < sizeof(struct erofs_xattr_ibody_header)) {
 		if (vi->xattr_isize) {
 			erofs_err(inode->i_sb,
 				  "bogus xattr ibody @ nid %llu", vi->nid);
 			DBG_BUGON(1);
 			ret = -EFSCORRUPTED;
 			goto out_unlock;	/* xattr ondisk layout error */
 		}
 		ret = -ENOATTR;
 		goto out_unlock;
 	}

 	sb = inode->i_sb;
 	sbi = EROFS_SB(sb);
 	it.blkaddr = erofs_blknr(iloc(sbi, vi->nid) + vi->inode_isize);
 	it.ofs = erofs_blkoff(iloc(sbi, vi->nid) + vi->inode_isize);

 	it.page = erofs_get_meta_page(sb, it.blkaddr);
 	if (IS_ERR(it.page)) {
 		ret = PTR_ERR(it.page);
 		goto out_unlock;
 	}

 	/* read in shared xattr array (non-atomic, see kmalloc below) */
 	it.kaddr = kmap(it.page);
 	atomic_map = false;

 	ih = (struct erofs_xattr_ibody_header *)(it.kaddr + it.ofs);

 	vi->xattr_shared_count = ih->h_shared_count;
 	vi->xattr_shared_xattrs = kmalloc_array(vi->xattr_shared_count,
 						sizeof(uint), GFP_KERNEL);
 	if (!vi->xattr_shared_xattrs) {
 		xattr_iter_end(&it, atomic_map);
 		ret = -ENOMEM;
 		goto out_unlock;
 	}

 	/* let's skip ibody header */
 	it.ofs += sizeof(struct erofs_xattr_ibody_header);

 	for (i = 0; i < vi->xattr_shared_count; ++i) {
 		if (it.ofs >= EROFS_BLKSIZ) {
 			/* cannot be unaligned */
 			DBG_BUGON(it.ofs != EROFS_BLKSIZ);
 			xattr_iter_end(&it, atomic_map);

 			it.page = erofs_get_meta_page(sb, ++it.blkaddr);
 			if (IS_ERR(it.page)) {
 				kfree(vi->xattr_shared_xattrs);
 				vi->xattr_shared_xattrs = NULL;
 				ret = PTR_ERR(it.page);
 				goto out_unlock;
 			}

 			it.kaddr = kmap_atomic(it.page);
 			atomic_map = true;
 			it.ofs = 0;
 		}
 		vi->xattr_shared_xattrs[i] =
 			le32_to_cpu(*(__le32 *)(it.kaddr + it.ofs));
 		it.ofs += sizeof(__le32);
 	}
 	xattr_iter_end(&it, atomic_map);

 	/* paired with smp_mb() at the beginning of the function. */
 	smp_mb();
 	set_bit(EROFS_I_EA_INITED_BIT, &vi->flags);

 out_unlock:
 	clear_and_wake_up_bit(EROFS_I_BL_XATTR_BIT, &vi->flags);
 	return ret;
 }

 /*
  * the general idea for these return values is
  * if    0 is returned, go on processing the current xattr;
  *       1 (> 0) is returned, skip this round to process the next xattr;
  *    -err (< 0) is returned, an error (maybe ENOXATTR) occurred
  *                            and need to be handled
  */
 struct xattr_iter_handlers {
 	int (*entry)(struct xattr_iter *_it, struct erofs_xattr_entry *entry);
 	int (*name)(struct xattr_iter *_it, unsigned int processed, char *buf,
 		    unsigned int len);
 	int (*alloc_buffer)(struct xattr_iter *_it, unsigned int value_sz);
 	void (*value)(struct xattr_iter *_it, unsigned int processed, char *buf,
 		      unsigned int len);
 };

 static inline int xattr_iter_fixup(struct xattr_iter *it)
 {
 	if (it->ofs < EROFS_BLKSIZ)
 		return 0;

 	xattr_iter_end(it, true);

 	it->blkaddr += erofs_blknr(it->ofs);

 	it->page = erofs_get_meta_page(it->sb, it->blkaddr);
 	if (IS_ERR(it->page)) {
 		int err = PTR_ERR(it->page);

 		it->page = NULL;
 		return err;
 	}

 	it->kaddr = kmap_atomic(it->page);
 	it->ofs = erofs_blkoff(it->ofs);
 	return 0;
 }

 static int inline_xattr_iter_begin(struct xattr_iter *it,
 				   struct inode *inode)
 {
 	struct erofs_inode *const vi = EROFS_I(inode);
 	struct erofs_sb_info *const sbi = EROFS_SB(inode->i_sb);
 	unsigned int xattr_header_sz, inline_xattr_ofs;

 	xattr_header_sz = inlinexattr_header_size(inode);
 	if (xattr_header_sz >= vi->xattr_isize) {
 		DBG_BUGON(xattr_header_sz > vi->xattr_isize);
 		return -ENOATTR;
 	}

 	inline_xattr_ofs = vi->inode_isize + xattr_header_sz;

 	it->blkaddr = erofs_blknr(iloc(sbi, vi->nid) + inline_xattr_ofs);
 	it->ofs = erofs_blkoff(iloc(sbi, vi->nid) + inline_xattr_ofs);

 	it->page = erofs_get_meta_page(inode->i_sb, it->blkaddr);
 	if (IS_ERR(it->page))
 		return PTR_ERR(it->page);

 	it->kaddr = kmap_atomic(it->page);
 	return vi->xattr_isize - xattr_header_sz;
 }

 /*
  * Regardless of success or failure, `xattr_foreach' will end up with
  * `ofs' pointing to the next xattr item rather than an arbitrary position.
  */
 static int xattr_foreach(struct xattr_iter *it,
 			 const struct xattr_iter_handlers *op,
 			 unsigned int *tlimit)
 {
 	struct erofs_xattr_entry entry;
 	unsigned int value_sz, processed, slice;
 	int err;

 	/* 0. fixup blkaddr, ofs, ipage */
 	err = xattr_iter_fixup(it);
 	if (err)
 		return err;

 	/*
 	 * 1. read xattr entry to the memory,
 	 *    since we do EROFS_XATTR_ALIGN
 	 *    therefore entry should be in the page
 	 */
 	entry = *(struct erofs_xattr_entry *)(it->kaddr + it->ofs);
 	if (tlimit) {
 		unsigned int entry_sz = erofs_xattr_entry_size(&entry);

 		/* xattr on-disk corruption: xattr entry beyond xattr_isize */
 		if (*tlimit < entry_sz) {
 			DBG_BUGON(1);
 			return -EFSCORRUPTED;
 		}
 		*tlimit -= entry_sz;
 	}

 	it->ofs += sizeof(struct erofs_xattr_entry);
 	value_sz = le16_to_cpu(entry.e_value_size);

 	/* handle entry */
 	err = op->entry(it, &entry);
 	if (err) {
 		it->ofs += entry.e_name_len + value_sz;
 		goto out;
 	}

 	/* 2. handle xattr name (ofs will finally be at the end of name) */
 	processed = 0;

 	while (processed < entry.e_name_len) {
 		if (it->ofs >= EROFS_BLKSIZ) {
 			DBG_BUGON(it->ofs > EROFS_BLKSIZ);

 			err = xattr_iter_fixup(it);
 			if (err)
 				goto out;
 			it->ofs = 0;
 		}

 		slice = min_t(unsigned int, PAGE_SIZE - it->ofs,
 			      entry.e_name_len - processed);

 		/* handle name */
 		err = op->name(it, processed, it->kaddr + it->ofs, slice);
 		if (err) {
 			it->ofs += entry.e_name_len - processed + value_sz;
 			goto out;
 		}

 		it->ofs += slice;
 		processed += slice;
 	}

 	/* 3. handle xattr value */
 	processed = 0;

 	if (op->alloc_buffer) {
 		err = op->alloc_buffer(it, value_sz);
 		if (err) {
 			it->ofs += value_sz;
 			goto out;
 		}
 	}

 	while (processed < value_sz) {
 		if (it->ofs >= EROFS_BLKSIZ) {
 			DBG_BUGON(it->ofs > EROFS_BLKSIZ);

 			err = xattr_iter_fixup(it);
 			if (err)
 				goto out;
 			it->ofs = 0;
 		}

 		slice = min_t(unsigned int, PAGE_SIZE - it->ofs,
 			      value_sz - processed);
 		op->value(it, processed, it->kaddr + it->ofs, slice);
 		it->ofs += slice;
 		processed += slice;
 	}

 out:
 	/* xattrs should be 4-byte aligned (on-disk constraint) */
 	it->ofs = EROFS_XATTR_ALIGN(it->ofs);
 	return err < 0 ? err : 0;
 }

 struct getxattr_iter {
 	struct xattr_iter it;

 	char *buffer;
 	int buffer_size, index;
 	struct qstr name;
 };

 static int xattr_entrymatch(struct xattr_iter *_it,
 			    struct erofs_xattr_entry *entry)
 {
 	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);

 	return (it->index != entry->e_name_index ||
 		it->name.len != entry->e_name_len) ? -ENOATTR : 0;
 }

 static int xattr_namematch(struct xattr_iter *_it,
 			   unsigned int processed, char *buf, unsigned int len)
 {
 	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);

 	return memcmp(buf, it->name.name + processed, len) ? -ENOATTR : 0;
 }

 static int xattr_checkbuffer(struct xattr_iter *_it,
 			     unsigned int value_sz)
 {
 	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);
 	int err = it->buffer_size < value_sz ? -ERANGE : 0;

 	it->buffer_size = value_sz;
 	return !it->buffer ? 1 : err;
 }

 static void xattr_copyvalue(struct xattr_iter *_it,
 			    unsigned int processed,
 			    char *buf, unsigned int len)
 {
 	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);

 	memcpy(it->buffer + processed, buf, len);
 }

 static const struct xattr_iter_handlers find_xattr_handlers = {
 	.entry = xattr_entrymatch,
 	.name = xattr_namematch,
 	.alloc_buffer = xattr_checkbuffer,
 	.value = xattr_copyvalue
 };

 static int inline_getxattr(struct inode *inode, struct getxattr_iter *it)
 {
 	int ret;
 	unsigned int remaining;

 	ret = inline_xattr_iter_begin(&it->it, inode);
 	if (ret < 0)
 		return ret;

 	remaining = ret;
 	while (remaining) {
 		ret = xattr_foreach(&it->it, &find_xattr_handlers, &remaining);
 		if (ret != -ENOATTR)
 			break;
 	}
 	xattr_iter_end_final(&it->it);

 	return ret ? ret : it->buffer_size;
 }

 static int shared_getxattr(struct inode *inode, struct getxattr_iter *it)
 {
 	struct erofs_inode *const vi = EROFS_I(inode);
 	struct super_block *const sb = inode->i_sb;
 	struct erofs_sb_info *const sbi = EROFS_SB(sb);
 	unsigned int i;
 	int ret = -ENOATTR;

 	for (i = 0; i < vi->xattr_shared_count; ++i) {
 		erofs_blk_t blkaddr =
 			xattrblock_addr(sbi, vi->xattr_shared_xattrs[i]);

 		it->it.ofs = xattrblock_offset(sbi, vi->xattr_shared_xattrs[i]);

 		if (!i || blkaddr != it->it.blkaddr) {
 			if (i)
 				xattr_iter_end(&it->it, true);

 			it->it.page = erofs_get_meta_page(sb, blkaddr);
 			if (IS_ERR(it->it.page))
 				return PTR_ERR(it->it.page);

 			it->it.kaddr = kmap_atomic(it->it.page);
 			it->it.blkaddr = blkaddr;
 		}

 		ret = xattr_foreach(&it->it, &find_xattr_handlers, NULL);
 		if (ret != -ENOATTR)
 			break;
 	}
 	if (vi->xattr_shared_count)
 		xattr_iter_end_final(&it->it);

 	return ret ? ret : it->buffer_size;
 }

 static bool erofs_xattr_user_list(struct dentry *dentry)
 {
 	return test_opt(&EROFS_SB(dentry->d_sb)->opt, XATTR_USER);
 }

 static bool erofs_xattr_trusted_list(struct dentry *dentry)
 {
 	return capable(CAP_SYS_ADMIN);
 }

 int erofs_getxattr(struct inode *inode, int index,
 		   const char *name,
 		   void *buffer, size_t buffer_size)
 {
 	int ret;
 	struct getxattr_iter it;

 	if (!name)
 		return -EINVAL;

 	ret = init_inode_xattrs(inode);
 	if (ret)
 		return ret;

 	it.index = index;

 	it.name.len = strlen(name);
 	if (it.name.len > EROFS_NAME_LEN)
 		return -ERANGE;
 	it.name.name = name;

 	it.buffer = buffer;
 	it.buffer_size = buffer_size;

 	it.it.sb = inode->i_sb;
 	ret = inline_getxattr(inode, &it);
 	if (ret == -ENOATTR)
 		ret = shared_getxattr(inode, &it);
 	return ret;
 }

 static int erofs_xattr_generic_get(const struct xattr_handler *handler,
 				   struct dentry *unused, struct inode *inode,
 				   const char *name, void *buffer, size_t size,
 				   int flags)
 {
 	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);

 	switch (handler->flags) {
 	case EROFS_XATTR_INDEX_USER:
 		if (!test_opt(&sbi->opt, XATTR_USER))
 			return -EOPNOTSUPP;
 		break;
 	case EROFS_XATTR_INDEX_TRUSTED:
 		break;
 	case EROFS_XATTR_INDEX_SECURITY:
 		break;
 	default:
 		return -EINVAL;
 	}

 	return erofs_getxattr(inode, handler->flags, name, buffer, size);
 }

 const struct xattr_handler erofs_xattr_user_handler = {
 	.prefix	= XATTR_USER_PREFIX,
 	.flags	= EROFS_XATTR_INDEX_USER,
 	.list	= erofs_xattr_user_list,
 	.get	= erofs_xattr_generic_get,
 };

 const struct xattr_handler erofs_xattr_trusted_handler = {
 	.prefix	= XATTR_TRUSTED_PREFIX,
 	.flags	= EROFS_XATTR_INDEX_TRUSTED,
 	.list	= erofs_xattr_trusted_list,
 	.get	= erofs_xattr_generic_get,
 };

 #ifdef CONFIG_EROFS_FS_SECURITY
 const struct xattr_handler __maybe_unused erofs_xattr_security_handler = {
 	.prefix	= XATTR_SECURITY_PREFIX,
 	.flags	= EROFS_XATTR_INDEX_SECURITY,
 	.get	= erofs_xattr_generic_get,
 };
 #endif

 const struct xattr_handler *erofs_xattr_handlers[] = {
 	&erofs_xattr_user_handler,
 #ifdef CONFIG_EROFS_FS_POSIX_ACL
 	&posix_acl_access_xattr_handler,
 	&posix_acl_default_xattr_handler,
 #endif
 	&erofs_xattr_trusted_handler,
 #ifdef CONFIG_EROFS_FS_SECURITY
 	&erofs_xattr_security_handler,
 #endif
 	NULL,
 };

 struct listxattr_iter {
 	struct xattr_iter it;

 	struct dentry *dentry;
 	char *buffer;
 	int buffer_size, buffer_ofs;
 };

 static int xattr_entrylist(struct xattr_iter *_it,
 			   struct erofs_xattr_entry *entry)
 {
 	struct listxattr_iter *it =
 		container_of(_it, struct listxattr_iter, it);
 	unsigned int prefix_len;
 	const char *prefix;

 	const struct xattr_handler *h =
 		erofs_xattr_handler(entry->e_name_index);

 	if (!h || (h->list && !h->list(it->dentry)))
 		return 1;

 	prefix = xattr_prefix(h);
 	prefix_len = strlen(prefix);

 	if (!it->buffer) {
 		it->buffer_ofs += prefix_len + entry->e_name_len + 1;
 		return 1;
 	}

 	if (it->buffer_ofs + prefix_len
 		+ entry->e_name_len + 1 > it->buffer_size)
 		return -ERANGE;

 	memcpy(it->buffer + it->buffer_ofs, prefix, prefix_len);
 	it->buffer_ofs += prefix_len;
 	return 0;
 }

 static int xattr_namelist(struct xattr_iter *_it,
 			  unsigned int processed, char *buf, unsigned int len)
 {
 	struct listxattr_iter *it =
 		container_of(_it, struct listxattr_iter, it);

 	memcpy(it->buffer + it->buffer_ofs, buf, len);
 	it->buffer_ofs += len;
 	return 0;
 }

 static int xattr_skipvalue(struct xattr_iter *_it,
 			   unsigned int value_sz)
 {
 	struct listxattr_iter *it =
 		container_of(_it, struct listxattr_iter, it);

 	it->buffer[it->buffer_ofs++] = '\0';
 	return 1;
 }

 static const struct xattr_iter_handlers list_xattr_handlers = {
 	.entry = xattr_entrylist,
 	.name = xattr_namelist,
 	.alloc_buffer = xattr_skipvalue,
 	.value = NULL
 };

 static int inline_listxattr(struct listxattr_iter *it)
 {
 	int ret;
 	unsigned int remaining;

 	ret = inline_xattr_iter_begin(&it->it, d_inode(it->dentry));
 	if (ret < 0)
 		return ret;

 	remaining = ret;
 	while (remaining) {
 		ret = xattr_foreach(&it->it, &list_xattr_handlers, &remaining);
 		if (ret)
 			break;
 	}
 	xattr_iter_end_final(&it->it);
 	return ret ? ret : it->buffer_ofs;
 }

 static int shared_listxattr(struct listxattr_iter *it)
 {
 	struct inode *const inode = d_inode(it->dentry);
 	struct erofs_inode *const vi = EROFS_I(inode);
 	struct super_block *const sb = inode->i_sb;
 	struct erofs_sb_info *const sbi = EROFS_SB(sb);
 	unsigned int i;
 	int ret = 0;

 	for (i = 0; i < vi->xattr_shared_count; ++i) {
 		erofs_blk_t blkaddr =
 			xattrblock_addr(sbi, vi->xattr_shared_xattrs[i]);

 		it->it.ofs = xattrblock_offset(sbi, vi->xattr_shared_xattrs[i]);
 		if (!i || blkaddr != it->it.blkaddr) {
 			if (i)
 				xattr_iter_end(&it->it, true);

 			it->it.page = erofs_get_meta_page(sb, blkaddr);
 			if (IS_ERR(it->it.page))
 				return PTR_ERR(it->it.page);

 			it->it.kaddr = kmap_atomic(it->it.page);
 			it->it.blkaddr = blkaddr;
 		}

 		ret = xattr_foreach(&it->it, &list_xattr_handlers, NULL);
 		if (ret)
 			break;
 	}
 	if (vi->xattr_shared_count)
 		xattr_iter_end_final(&it->it);

 	return ret ? ret : it->buffer_ofs;
 }

 ssize_t erofs_listxattr(struct dentry *dentry,
 			char *buffer, size_t buffer_size)
 {
 	int ret;
 	struct listxattr_iter it;

 	ret = init_inode_xattrs(d_inode(dentry));
 	if (ret == -ENOATTR)
 		return 0;
 	if (ret)
 		return ret;

 	it.dentry = dentry;
 	it.buffer = buffer;
 	it.buffer_size = buffer_size;
 	it.buffer_ofs = 0;

 	it.it.sb = dentry->d_sb;

 	ret = inline_listxattr(&it);
 	if (ret < 0 && ret != -ENOATTR)
 		return ret;
 	return shared_listxattr(&it);
 }

 #ifdef CONFIG_EROFS_FS_POSIX_ACL
 struct posix_acl *erofs_get_acl(struct inode *inode, int type)
 {
 	struct posix_acl *acl;
 	int prefix, rc;
 	char *value = NULL;

 	switch (type) {
 	case ACL_TYPE_ACCESS:
 		prefix = EROFS_XATTR_INDEX_POSIX_ACL_ACCESS;
 		break;
 	case ACL_TYPE_DEFAULT:
 		prefix = EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT;
 		break;
 	default:
 		return ERR_PTR(-EINVAL);
 	}

 	rc = erofs_getxattr(inode, prefix, "", NULL, 0);
 	if (rc > 0) {
 		value = kmalloc(rc, GFP_KERNEL);
 		if (!value)
 			return ERR_PTR(-ENOMEM);
 		rc = erofs_getxattr(inode, prefix, "", value, rc);
 	}

 	if (rc == -ENOATTR)
 		acl = NULL;
 	else if (rc < 0)
 		acl = ERR_PTR(rc);
 	else
 		acl = posix_acl_from_xattr(&init_user_ns, value, rc);
 	kfree(value);
 	return acl;
 }
 #endif
	// SPDX-License-Identifier: GPL-2.0-only
	/*
	* Copyright (C) 2017-2018 HUAWEI, Inc.
	* https://www.huawei.com/
	*/
	#include <linux/security.h>
	#include "xattr.h"

	struct xattr_iter {
	struct super_block *sb;
	struct page *page;
	void *kaddr;

	erofs_blk_t blkaddr;
	unsigned int ofs;
	};

	static inline void xattr_iter_end(struct xattr_iter *it, bool atomic)
	{
	/* the only user of kunmap() is 'init_inode_xattrs' */
	if (!atomic)
	kunmap(it->page);
	else
	kunmap_atomic(it->kaddr);

	unlock_page(it->page);
	put_page(it->page);
	}

	static inline void xattr_iter_end_final(struct xattr_iter *it)
	{
	if (!it->page)
	return;

	xattr_iter_end(it, true);
	}

	static int init_inode_xattrs(struct inode *inode)
	{
	struct erofs_inode *const vi = EROFS_I(inode);
	struct xattr_iter it;
	unsigned int i;
	struct erofs_xattr_ibody_header *ih;
	struct super_block *sb;
	struct erofs_sb_info *sbi;
	bool atomic_map;
	int ret = 0;

	/* the most case is that xattrs of this inode are initialized. */
	if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags)) {
	/*
	* paired with smp_mb() at the end of the function to ensure
	* fields will only be observed after the bit is set.
	*/
	smp_mb();
	return 0;
	}

	if (wait_on_bit_lock(&vi->flags, EROFS_I_BL_XATTR_BIT, TASK_KILLABLE))
	return -ERESTARTSYS;

	/* someone has initialized xattrs for us? */
	if (test_bit(EROFS_I_EA_INITED_BIT, &vi->flags))
	goto out_unlock;

	/*
	* bypass all xattr operations if ->xattr_isize is not greater than
	* sizeof(struct erofs_xattr_ibody_header), in detail:
	* 1) it is not enough to contain erofs_xattr_ibody_header then
	* ->xattr_isize should be 0 (it means no xattr);
	* 2) it is just to contain erofs_xattr_ibody_header, which is on-disk
	* undefined right now (maybe use later with some new sb feature).
	*/
	if (vi->xattr_isize == sizeof(struct erofs_xattr_ibody_header)) {
	erofs_err(inode->i_sb,
	"xattr_isize %d of nid %llu is not supported yet",
	vi->xattr_isize, vi->nid);
	ret = -EOPNOTSUPP;
	goto out_unlock;
	} else if (vi->xattr_isize < sizeof(struct erofs_xattr_ibody_header)) {
	if (vi->xattr_isize) {
	erofs_err(inode->i_sb,
	"bogus xattr ibody @ nid %llu", vi->nid);
	DBG_BUGON(1);
	ret = -EFSCORRUPTED;
	goto out_unlock; /* xattr ondisk layout error */
	}
	ret = -ENOATTR;
	goto out_unlock;
	}

	sb = inode->i_sb;
	sbi = EROFS_SB(sb);
	it.blkaddr = erofs_blknr(iloc(sbi, vi->nid) + vi->inode_isize);
	it.ofs = erofs_blkoff(iloc(sbi, vi->nid) + vi->inode_isize);

	it.page = erofs_get_meta_page(sb, it.blkaddr);
	if (IS_ERR(it.page)) {
	ret = PTR_ERR(it.page);
	goto out_unlock;
	}

	/* read in shared xattr array (non-atomic, see kmalloc below) */
	it.kaddr = kmap(it.page);
	atomic_map = false;

	ih = (struct erofs_xattr_ibody_header *)(it.kaddr + it.ofs);

	vi->xattr_shared_count = ih->h_shared_count;
	vi->xattr_shared_xattrs = kmalloc_array(vi->xattr_shared_count,
	sizeof(uint), GFP_KERNEL);
	if (!vi->xattr_shared_xattrs) {
	xattr_iter_end(&it, atomic_map);
	ret = -ENOMEM;
	goto out_unlock;
	}

	/* let's skip ibody header */
	it.ofs += sizeof(struct erofs_xattr_ibody_header);

	for (i = 0; i < vi->xattr_shared_count; ++i) {
	if (it.ofs >= EROFS_BLKSIZ) {
	/* cannot be unaligned */
	DBG_BUGON(it.ofs != EROFS_BLKSIZ);
	xattr_iter_end(&it, atomic_map);

	it.page = erofs_get_meta_page(sb, ++it.blkaddr);
	if (IS_ERR(it.page)) {
	kfree(vi->xattr_shared_xattrs);
	vi->xattr_shared_xattrs = NULL;
	ret = PTR_ERR(it.page);
	goto out_unlock;
	}

	it.kaddr = kmap_atomic(it.page);
	atomic_map = true;
	it.ofs = 0;
	}
	vi->xattr_shared_xattrs[i] =
	le32_to_cpu((__le32 )(it.kaddr + it.ofs));
	it.ofs += sizeof(__le32);
	}
	xattr_iter_end(&it, atomic_map);

	/* paired with smp_mb() at the beginning of the function. */
	smp_mb();
	set_bit(EROFS_I_EA_INITED_BIT, &vi->flags);

	out_unlock:
	clear_and_wake_up_bit(EROFS_I_BL_XATTR_BIT, &vi->flags);
	return ret;
	}

	/*
	* the general idea for these return values is
	* if 0 is returned, go on processing the current xattr;
	* 1 (> 0) is returned, skip this round to process the next xattr;
	* -err (< 0) is returned, an error (maybe ENOXATTR) occurred
	* and need to be handled
	*/
	struct xattr_iter_handlers {
	int (entry)(struct xattr_iter _it, struct erofs_xattr_entry *entry);
	int (name)(struct xattr_iter _it, unsigned int processed, char *buf,
	unsigned int len);
	int (alloc_buffer)(struct xattr_iter _it, unsigned int value_sz);
	void (value)(struct xattr_iter _it, unsigned int processed, char *buf,
	unsigned int len);
	};

	static inline int xattr_iter_fixup(struct xattr_iter *it)
	{
	if (it->ofs < EROFS_BLKSIZ)
	return 0;

	xattr_iter_end(it, true);

	it->blkaddr += erofs_blknr(it->ofs);

	it->page = erofs_get_meta_page(it->sb, it->blkaddr);
	if (IS_ERR(it->page)) {
	int err = PTR_ERR(it->page);

	it->page = NULL;
	return err;
	}

	it->kaddr = kmap_atomic(it->page);
	it->ofs = erofs_blkoff(it->ofs);
	return 0;
	}

	static int inline_xattr_iter_begin(struct xattr_iter *it,
	struct inode *inode)
	{
	struct erofs_inode *const vi = EROFS_I(inode);
	struct erofs_sb_info *const sbi = EROFS_SB(inode->i_sb);
	unsigned int xattr_header_sz, inline_xattr_ofs;

	xattr_header_sz = inlinexattr_header_size(inode);
	if (xattr_header_sz >= vi->xattr_isize) {
	DBG_BUGON(xattr_header_sz > vi->xattr_isize);
	return -ENOATTR;
	}

	inline_xattr_ofs = vi->inode_isize + xattr_header_sz;

	it->blkaddr = erofs_blknr(iloc(sbi, vi->nid) + inline_xattr_ofs);
	it->ofs = erofs_blkoff(iloc(sbi, vi->nid) + inline_xattr_ofs);

	it->page = erofs_get_meta_page(inode->i_sb, it->blkaddr);
	if (IS_ERR(it->page))
	return PTR_ERR(it->page);

	it->kaddr = kmap_atomic(it->page);
	return vi->xattr_isize - xattr_header_sz;
	}

	/*
	* Regardless of success or failure, `xattr_foreach' will end up with
	* `ofs' pointing to the next xattr item rather than an arbitrary position.
	*/
	static int xattr_foreach(struct xattr_iter *it,
	const struct xattr_iter_handlers *op,
	unsigned int *tlimit)
	{
	struct erofs_xattr_entry entry;
	unsigned int value_sz, processed, slice;
	int err;

	/* 0. fixup blkaddr, ofs, ipage */
	err = xattr_iter_fixup(it);
	if (err)
	return err;

	/*
	* 1. read xattr entry to the memory,
	* since we do EROFS_XATTR_ALIGN
	* therefore entry should be in the page
	*/
	entry = (struct erofs_xattr_entry )(it->kaddr + it->ofs);
	if (tlimit) {
	unsigned int entry_sz = erofs_xattr_entry_size(&entry);

	/* xattr on-disk corruption: xattr entry beyond xattr_isize */
	if (*tlimit < entry_sz) {
	DBG_BUGON(1);
	return -EFSCORRUPTED;
	}
	*tlimit -= entry_sz;
	}

	it->ofs += sizeof(struct erofs_xattr_entry);
	value_sz = le16_to_cpu(entry.e_value_size);

	/* handle entry */
	err = op->entry(it, &entry);
	if (err) {
	it->ofs += entry.e_name_len + value_sz;
	goto out;
	}

	/* 2. handle xattr name (ofs will finally be at the end of name) */
	processed = 0;

	while (processed < entry.e_name_len) {
	if (it->ofs >= EROFS_BLKSIZ) {
	DBG_BUGON(it->ofs > EROFS_BLKSIZ);

	err = xattr_iter_fixup(it);
	if (err)
	goto out;
	it->ofs = 0;
	}

	slice = min_t(unsigned int, PAGE_SIZE - it->ofs,
	entry.e_name_len - processed);

	/* handle name */
	err = op->name(it, processed, it->kaddr + it->ofs, slice);
	if (err) {
	it->ofs += entry.e_name_len - processed + value_sz;
	goto out;
	}

	it->ofs += slice;
	processed += slice;
	}

	/* 3. handle xattr value */
	processed = 0;

	if (op->alloc_buffer) {
	err = op->alloc_buffer(it, value_sz);
	if (err) {
	it->ofs += value_sz;
	goto out;
	}
	}

	while (processed < value_sz) {
	if (it->ofs >= EROFS_BLKSIZ) {
	DBG_BUGON(it->ofs > EROFS_BLKSIZ);

	err = xattr_iter_fixup(it);
	if (err)
	goto out;
	it->ofs = 0;
	}

	slice = min_t(unsigned int, PAGE_SIZE - it->ofs,
	value_sz - processed);
	op->value(it, processed, it->kaddr + it->ofs, slice);
	it->ofs += slice;
	processed += slice;
	}

	out:
	/* xattrs should be 4-byte aligned (on-disk constraint) */
	it->ofs = EROFS_XATTR_ALIGN(it->ofs);
	return err < 0 ? err : 0;
	}

	struct getxattr_iter {
	struct xattr_iter it;

	char *buffer;
	int buffer_size, index;
	struct qstr name;
	};

	static int xattr_entrymatch(struct xattr_iter *_it,
	struct erofs_xattr_entry *entry)
	{
	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);

	return (it->index != entry->e_name_index \|\|
	it->name.len != entry->e_name_len) ? -ENOATTR : 0;
	}

	static int xattr_namematch(struct xattr_iter *_it,
	unsigned int processed, char *buf, unsigned int len)
	{
	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);

	return memcmp(buf, it->name.name + processed, len) ? -ENOATTR : 0;
	}

	static int xattr_checkbuffer(struct xattr_iter *_it,
	unsigned int value_sz)
	{
	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);
	int err = it->buffer_size < value_sz ? -ERANGE : 0;

	it->buffer_size = value_sz;
	return !it->buffer ? 1 : err;
	}

	static void xattr_copyvalue(struct xattr_iter *_it,
	unsigned int processed,
	char *buf, unsigned int len)
	{
	struct getxattr_iter *it = container_of(_it, struct getxattr_iter, it);

	memcpy(it->buffer + processed, buf, len);
	}

	static const struct xattr_iter_handlers find_xattr_handlers = {
	.entry = xattr_entrymatch,
	.name = xattr_namematch,
	.alloc_buffer = xattr_checkbuffer,
	.value = xattr_copyvalue
	};

	static int inline_getxattr(struct inode inode, struct getxattr_iter it)
	{
	int ret;
	unsigned int remaining;

	ret = inline_xattr_iter_begin(&it->it, inode);
	if (ret < 0)
	return ret;

	remaining = ret;
	while (remaining) {
	ret = xattr_foreach(&it->it, &find_xattr_handlers, &remaining);
	if (ret != -ENOATTR)
	break;
	}
	xattr_iter_end_final(&it->it);

	return ret ? ret : it->buffer_size;
	}

	static int shared_getxattr(struct inode inode, struct getxattr_iter it)
	{
	struct erofs_inode *const vi = EROFS_I(inode);
	struct super_block *const sb = inode->i_sb;
	struct erofs_sb_info *const sbi = EROFS_SB(sb);
	unsigned int i;
	int ret = -ENOATTR;

	for (i = 0; i < vi->xattr_shared_count; ++i) {
	erofs_blk_t blkaddr =
	xattrblock_addr(sbi, vi->xattr_shared_xattrs[i]);

	it->it.ofs = xattrblock_offset(sbi, vi->xattr_shared_xattrs[i]);

	if (!i \|\| blkaddr != it->it.blkaddr) {
	if (i)
	xattr_iter_end(&it->it, true);

	it->it.page = erofs_get_meta_page(sb, blkaddr);
	if (IS_ERR(it->it.page))
	return PTR_ERR(it->it.page);

	it->it.kaddr = kmap_atomic(it->it.page);
	it->it.blkaddr = blkaddr;
	}

	ret = xattr_foreach(&it->it, &find_xattr_handlers, NULL);
	if (ret != -ENOATTR)
	break;
	}
	if (vi->xattr_shared_count)
	xattr_iter_end_final(&it->it);

	return ret ? ret : it->buffer_size;
	}

	static bool erofs_xattr_user_list(struct dentry *dentry)
	{
	return test_opt(&EROFS_SB(dentry->d_sb)->opt, XATTR_USER);
	}

	static bool erofs_xattr_trusted_list(struct dentry *dentry)
	{
	return capable(CAP_SYS_ADMIN);
	}

	int erofs_getxattr(struct inode *inode, int index,
	const char *name,
	void *buffer, size_t buffer_size)
	{
	int ret;
	struct getxattr_iter it;

	if (!name)
	return -EINVAL;

	ret = init_inode_xattrs(inode);
	if (ret)
	return ret;

	it.index = index;

	it.name.len = strlen(name);
	if (it.name.len > EROFS_NAME_LEN)
	return -ERANGE;
	it.name.name = name;

	it.buffer = buffer;
	it.buffer_size = buffer_size;

	it.it.sb = inode->i_sb;
	ret = inline_getxattr(inode, &it);
	if (ret == -ENOATTR)
	ret = shared_getxattr(inode, &it);
	return ret;
	}

	static int erofs_xattr_generic_get(const struct xattr_handler *handler,
	struct dentry unused, struct inode inode,
	const char name, void buffer, size_t size,
	int flags)
	{
	struct erofs_sb_info *const sbi = EROFS_I_SB(inode);

	switch (handler->flags) {
	case EROFS_XATTR_INDEX_USER:
	if (!test_opt(&sbi->opt, XATTR_USER))
	return -EOPNOTSUPP;
	break;
	case EROFS_XATTR_INDEX_TRUSTED:
	break;
	case EROFS_XATTR_INDEX_SECURITY:
	break;
	default:
	return -EINVAL;
	}

	return erofs_getxattr(inode, handler->flags, name, buffer, size);
	}

	const struct xattr_handler erofs_xattr_user_handler = {
	.prefix = XATTR_USER_PREFIX,
	.flags = EROFS_XATTR_INDEX_USER,
	.list = erofs_xattr_user_list,
	.get = erofs_xattr_generic_get,
	};

	const struct xattr_handler erofs_xattr_trusted_handler = {
	.prefix = XATTR_TRUSTED_PREFIX,
	.flags = EROFS_XATTR_INDEX_TRUSTED,
	.list = erofs_xattr_trusted_list,
	.get = erofs_xattr_generic_get,
	};

	#ifdef CONFIG_EROFS_FS_SECURITY
	const struct xattr_handler __maybe_unused erofs_xattr_security_handler = {
	.prefix = XATTR_SECURITY_PREFIX,
	.flags = EROFS_XATTR_INDEX_SECURITY,
	.get = erofs_xattr_generic_get,
	};
	#endif

	const struct xattr_handler *erofs_xattr_handlers[] = {
	&erofs_xattr_user_handler,
	#ifdef CONFIG_EROFS_FS_POSIX_ACL
	&posix_acl_access_xattr_handler,
	&posix_acl_default_xattr_handler,
	#endif
	&erofs_xattr_trusted_handler,
	#ifdef CONFIG_EROFS_FS_SECURITY
	&erofs_xattr_security_handler,
	#endif
	NULL,
	};

	struct listxattr_iter {
	struct xattr_iter it;

	struct dentry *dentry;
	char *buffer;
	int buffer_size, buffer_ofs;
	};

	static int xattr_entrylist(struct xattr_iter *_it,
	struct erofs_xattr_entry *entry)
	{
	struct listxattr_iter *it =
	container_of(_it, struct listxattr_iter, it);
	unsigned int prefix_len;
	const char *prefix;

	const struct xattr_handler *h =
	erofs_xattr_handler(entry->e_name_index);

	if (!h \|\| (h->list && !h->list(it->dentry)))
	return 1;

	prefix = xattr_prefix(h);
	prefix_len = strlen(prefix);

	if (!it->buffer) {
	it->buffer_ofs += prefix_len + entry->e_name_len + 1;
	return 1;
	}

	if (it->buffer_ofs + prefix_len
	+ entry->e_name_len + 1 > it->buffer_size)
	return -ERANGE;

	memcpy(it->buffer + it->buffer_ofs, prefix, prefix_len);
	it->buffer_ofs += prefix_len;
	return 0;
	}

	static int xattr_namelist(struct xattr_iter *_it,
	unsigned int processed, char *buf, unsigned int len)
	{
	struct listxattr_iter *it =
	container_of(_it, struct listxattr_iter, it);

	memcpy(it->buffer + it->buffer_ofs, buf, len);
	it->buffer_ofs += len;
	return 0;
	}

	static int xattr_skipvalue(struct xattr_iter *_it,
	unsigned int value_sz)
	{
	struct listxattr_iter *it =
	container_of(_it, struct listxattr_iter, it);

	it->buffer[it->buffer_ofs++] = '\0';
	return 1;
	}

	static const struct xattr_iter_handlers list_xattr_handlers = {
	.entry = xattr_entrylist,
	.name = xattr_namelist,
	.alloc_buffer = xattr_skipvalue,
	.value = NULL
	};

	static int inline_listxattr(struct listxattr_iter *it)
	{
	int ret;
	unsigned int remaining;

	ret = inline_xattr_iter_begin(&it->it, d_inode(it->dentry));
	if (ret < 0)
	return ret;

	remaining = ret;
	while (remaining) {
	ret = xattr_foreach(&it->it, &list_xattr_handlers, &remaining);
	if (ret)
	break;
	}
	xattr_iter_end_final(&it->it);
	return ret ? ret : it->buffer_ofs;
	}

	static int shared_listxattr(struct listxattr_iter *it)
	{
	struct inode *const inode = d_inode(it->dentry);
	struct erofs_inode *const vi = EROFS_I(inode);
	struct super_block *const sb = inode->i_sb;
	struct erofs_sb_info *const sbi = EROFS_SB(sb);
	unsigned int i;
	int ret = 0;

	for (i = 0; i < vi->xattr_shared_count; ++i) {
	erofs_blk_t blkaddr =
	xattrblock_addr(sbi, vi->xattr_shared_xattrs[i]);

	it->it.ofs = xattrblock_offset(sbi, vi->xattr_shared_xattrs[i]);
	if (!i \|\| blkaddr != it->it.blkaddr) {
	if (i)
	xattr_iter_end(&it->it, true);

	it->it.page = erofs_get_meta_page(sb, blkaddr);
	if (IS_ERR(it->it.page))
	return PTR_ERR(it->it.page);

	it->it.kaddr = kmap_atomic(it->it.page);
	it->it.blkaddr = blkaddr;
	}

	ret = xattr_foreach(&it->it, &list_xattr_handlers, NULL);
	if (ret)
	break;
	}
	if (vi->xattr_shared_count)
	xattr_iter_end_final(&it->it);

	return ret ? ret : it->buffer_ofs;
	}

	ssize_t erofs_listxattr(struct dentry *dentry,
	char *buffer, size_t buffer_size)
	{
	int ret;
	struct listxattr_iter it;

	ret = init_inode_xattrs(d_inode(dentry));
	if (ret == -ENOATTR)
	return 0;
	if (ret)
	return ret;

	it.dentry = dentry;
	it.buffer = buffer;
	it.buffer_size = buffer_size;
	it.buffer_ofs = 0;

	it.it.sb = dentry->d_sb;

	ret = inline_listxattr(&it);
	if (ret < 0 && ret != -ENOATTR)
	return ret;
	return shared_listxattr(&it);
	}

	#ifdef CONFIG_EROFS_FS_POSIX_ACL
	struct posix_acl erofs_get_acl(struct inode inode, int type)
	{
	struct posix_acl *acl;
	int prefix, rc;
	char *value = NULL;

	switch (type) {
	case ACL_TYPE_ACCESS:
	prefix = EROFS_XATTR_INDEX_POSIX_ACL_ACCESS;
	break;
	case ACL_TYPE_DEFAULT:
	prefix = EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT;
	break;
	default:
	return ERR_PTR(-EINVAL);
	}

	rc = erofs_getxattr(inode, prefix, "", NULL, 0);
	if (rc > 0) {
	value = kmalloc(rc, GFP_KERNEL);
	if (!value)
	return ERR_PTR(-ENOMEM);
	rc = erofs_getxattr(inode, prefix, "", value, rc);
	}

	if (rc == -ENOATTR)
	acl = NULL;
	else if (rc < 0)
	acl = ERR_PTR(rc);
	else
	acl = posix_acl_from_xattr(&init_user_ns, value, rc);
	kfree(value);
	return acl;
	}
	#endif