lib/xattr.c - platform/external/erofs-utils - Git at Google

 // SPDX-License-Identifier: GPL-2.0+
 /*
  * erofs-utils/lib/xattr.c
  *
  * Originally contributed by an anonymous person,
  * heavily changed by Li Guifu <blucerlee@gmail.com>
  *                and Gao Xiang <hsiangkao@aol.com>
  */
 #define _GNU_SOURCE
 #include <stdlib.h>
 #include <sys/xattr.h>
 #ifdef HAVE_LINUX_XATTR_H
 #include <linux/xattr.h>
 #endif
 #include <sys/stat.h>
 #include <dirent.h>
 #include "erofs/print.h"
 #include "erofs/hashtable.h"
 #include "erofs/xattr.h"
 #include "erofs/cache.h"
 #include "erofs/io.h"

 #define EA_HASHTABLE_BITS 16

 struct xattr_item {
 	const char *kvbuf;
 	unsigned int hash[2], len[2], count;
 	int shared_xattr_id;
 	u8 prefix;
 	struct hlist_node node;
 };

 struct inode_xattr_node {
 	struct list_head list;
 	struct xattr_item *item;
 };

 static DECLARE_HASHTABLE(ea_hashtable, EA_HASHTABLE_BITS);

 static LIST_HEAD(shared_xattrs_list);
 static unsigned int shared_xattrs_count, shared_xattrs_size;

 static struct xattr_prefix {
 	const char *prefix;
 	u16 prefix_len;
 } xattr_types[] = {
 	[EROFS_XATTR_INDEX_USER] = {
 		XATTR_USER_PREFIX,
 		XATTR_USER_PREFIX_LEN
 	}, [EROFS_XATTR_INDEX_POSIX_ACL_ACCESS] = {
 		XATTR_NAME_POSIX_ACL_ACCESS,
 		sizeof(XATTR_NAME_POSIX_ACL_ACCESS) - 1
 	}, [EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT] = {
 		XATTR_NAME_POSIX_ACL_DEFAULT,
 		sizeof(XATTR_NAME_POSIX_ACL_DEFAULT) - 1
 	}, [EROFS_XATTR_INDEX_TRUSTED] = {
 		XATTR_TRUSTED_PREFIX,
 		XATTR_TRUSTED_PREFIX_LEN
 	}, [EROFS_XATTR_INDEX_SECURITY] = {
 		XATTR_SECURITY_PREFIX,
 		XATTR_SECURITY_PREFIX_LEN
 	}
 };

 static unsigned int BKDRHash(char *str, unsigned int len)
 {
 	const unsigned int seed = 131313;
 	unsigned int hash = 0;

 	while (len) {
 		hash = hash * seed + (*str++);
 		--len;
 	}
 	return hash;
 }

 static unsigned int xattr_item_hash(u8 prefix, char *buf,
 				    unsigned int len[2], unsigned int hash[2])
 {
 	hash[0] = BKDRHash(buf, len[0]);	/* key */
 	hash[1] = BKDRHash(buf + len[0], len[1]);	/* value */

 	return prefix ^ hash[0] ^ hash[1];
 }

 static unsigned int put_xattritem(struct xattr_item *item)
 {
 	if (item->count > 1)
 		return --item->count;
 	free(item);
 	return 0;
 }

 static struct xattr_item *get_xattritem(u8 prefix, char *kvbuf,
 					unsigned int len[2])
 {
 	struct xattr_item *item;
 	unsigned int hash[2], hkey;

 	hkey = xattr_item_hash(prefix, kvbuf, len, hash);

 	hash_for_each_possible(ea_hashtable, item, node, hkey) {
 		if (prefix == item->prefix &&
 		    item->len[0] == len[0] && item->len[1] == len[1] &&
 		    item->hash[0] == hash[0] && item->hash[1] == hash[1] &&
 		    !memcmp(kvbuf, item->kvbuf, len[0] + len[1])) {
 			free(kvbuf);
 			++item->count;
 			return item;
 		}
 	}

 	item = malloc(sizeof(*item));
 	if (!item) {
 		free(kvbuf);
 		return ERR_PTR(-ENOMEM);
 	}
 	INIT_HLIST_NODE(&item->node);
 	item->count = 1;
 	item->kvbuf = kvbuf;
 	item->len[0] = len[0];
 	item->len[1] = len[1];
 	item->hash[0] = hash[0];
 	item->hash[1] = hash[1];
 	item->shared_xattr_id = -1;
 	item->prefix = prefix;
 	hash_add(ea_hashtable, &item->node, hkey);
 	return item;
 }

 static bool match_prefix(const char *key, u8 *index, u16 *len)
 {
 	struct xattr_prefix *p;

 	for (p = xattr_types; p < xattr_types + ARRAY_SIZE(xattr_types); ++p) {
 		if (p->prefix && !strncmp(p->prefix, key, p->prefix_len)) {
 			*len = p->prefix_len;
 			*index = p - xattr_types;
 			return true;
 		}
 	}
 	return false;
 }

 static struct xattr_item *parse_one_xattr(const char *path, const char *key,
 					  unsigned int keylen)
 {
 	ssize_t ret;
 	u8 prefix;
 	u16 prefixlen;
 	unsigned int len[2];
 	char *kvbuf;

 	erofs_dbg("parse xattr [%s] of %s", path, key);

 	if (!match_prefix(key, &prefix, &prefixlen))
 		return ERR_PTR(-ENODATA);

 	DBG_BUGON(keylen < prefixlen);

 	/* determine length of the value */
 	ret = lgetxattr(path, key, NULL, 0);
 	if (ret < 0)
 		return ERR_PTR(-errno);
 	len[1] = ret;

 	/* allocate key-value buffer */
 	len[0] = keylen - prefixlen;

 	kvbuf = malloc(len[0] + len[1]);
 	if (!kvbuf)
 		return ERR_PTR(-ENOMEM);
 	memcpy(kvbuf, key + prefixlen, len[0]);
 	if (len[1]) {
 		/* copy value to buffer */
 		ret = lgetxattr(path, key, kvbuf + len[0], len[1]);
 		if (ret < 0) {
 			free(kvbuf);
 			return ERR_PTR(-errno);
 		}
 		if (len[1] != ret) {
 			erofs_err("size of xattr value got changed just now (%u-> %ld)",
 				  len[1], (long)ret);
 			len[1] = ret;
 		}
 	}
 	return get_xattritem(prefix, kvbuf, len);
 }

 static struct xattr_item *erofs_get_selabel_xattr(const char *srcpath,
 						  mode_t mode)
 {
 #ifdef HAVE_LIBSELINUX
 	if (cfg.sehnd) {
 		char *secontext;
 		int ret;
 		unsigned int len[2];
 		char *kvbuf, *fspath;

 #ifdef WITH_ANDROID
 		if (cfg.mount_point)
 			ret = asprintf(&fspath, "/%s/%s", cfg.mount_point,
 				       erofs_fspath(srcpath));
 		else
 #endif
 		ret = asprintf(&fspath, "/%s", erofs_fspath(srcpath));
 		if (ret <= 0)
 			return ERR_PTR(-ENOMEM);

 		ret = selabel_lookup(cfg.sehnd, &secontext, fspath, mode);
 		free(fspath);

 		if (ret) {
 			ret = -errno;
 			if (ret != -ENOENT) {
 				erofs_err("failed to lookup selabel for %s: %s",
 					  srcpath, erofs_strerror(ret));
 				return ERR_PTR(ret);
 			}
 			/* secontext = "u:object_r:unlabeled:s0"; */
 			return NULL;
 		}

 		len[0] = sizeof("selinux") - 1;
 		len[1] = strlen(secontext);
 		kvbuf = malloc(len[0] + len[1] + 1);
 		if (!kvbuf) {
 			freecon(secontext);
 			return ERR_PTR(-ENOMEM);
 		}
 		sprintf(kvbuf, "selinux%s", secontext);
 		freecon(secontext);
 		return get_xattritem(EROFS_XATTR_INDEX_SECURITY, kvbuf, len);
 	}
 #endif
 	return NULL;
 }

 static int inode_xattr_add(struct list_head *hlist, struct xattr_item *item)
 {
 	struct inode_xattr_node *node = malloc(sizeof(*node));

 	if (!node)
 		return -ENOMEM;
 	init_list_head(&node->list);
 	node->item = item;
 	list_add(&node->list, hlist);
 	return 0;
 }

 static int shared_xattr_add(struct xattr_item *item)
 {
 	struct inode_xattr_node *node = malloc(sizeof(*node));

 	if (!node)
 		return -ENOMEM;

 	init_list_head(&node->list);
 	node->item = item;
 	list_add(&node->list, &shared_xattrs_list);

 	shared_xattrs_size += sizeof(struct erofs_xattr_entry);
 	shared_xattrs_size = EROFS_XATTR_ALIGN(shared_xattrs_size +
 					       item->len[0] + item->len[1]);
 	return ++shared_xattrs_count;
 }

 static int erofs_xattr_add(struct list_head *ixattrs, struct xattr_item *item)
 {
 	if (ixattrs)
 		return inode_xattr_add(ixattrs, item);

 	if (item->count == cfg.c_inline_xattr_tolerance + 1) {
 		int ret = shared_xattr_add(item);

 		if (ret < 0)
 			return ret;
 	}
 	return 0;
 }

 static bool erofs_is_skipped_xattr(const char *key)
 {
 #ifdef HAVE_LIBSELINUX
 	/* if sehnd is valid, selabels will be overridden */
 	if (cfg.sehnd && !strcmp(key, XATTR_SECURITY_PREFIX "selinux"))
 		return true;
 #endif
 	return false;
 }

 static int read_xattrs_from_file(const char *path, mode_t mode,
 				 struct list_head *ixattrs)
 {
 	ssize_t kllen = llistxattr(path, NULL, 0);
 	int ret;
 	char *keylst, *key, *klend;
 	unsigned int keylen;
 	struct xattr_item *item;

 	if (kllen < 0 && errno != ENODATA) {
 		erofs_err("llistxattr to get the size of names for %s failed",
 			  path);
 		return -errno;
 	}

 	ret = 0;
 	if (kllen <= 1)
 		goto out;

 	keylst = malloc(kllen);
 	if (!keylst)
 		return -ENOMEM;

 	/* copy the list of attribute keys to the buffer.*/
 	kllen = llistxattr(path, keylst, kllen);
 	if (kllen < 0) {
 		erofs_err("llistxattr to get names for %s failed", path);
 		ret = -errno;
 		goto err;
 	}

 	/*
 	 * loop over the list of zero terminated strings with the
 	 * attribute keys. Use the remaining buffer length to determine
 	 * the end of the list.
 	 */
 	klend = keylst + kllen;
 	ret = 0;

 	for (key = keylst; key != klend; key += keylen + 1) {
 		keylen = strlen(key);
 		if (erofs_is_skipped_xattr(key))
 			continue;

 		item = parse_one_xattr(path, key, keylen);
 		if (IS_ERR(item)) {
 			ret = PTR_ERR(item);
 			goto err;
 		}

 		ret = erofs_xattr_add(ixattrs, item);
 		if (ret < 0)
 			goto err;
 	}
 	free(keylst);

 out:
 	/* if some selabel is avilable, need to add right now */
 	item = erofs_get_selabel_xattr(path, mode);
 	if (IS_ERR(item))
 		return PTR_ERR(item);
 	if (item)
 		ret = erofs_xattr_add(ixattrs, item);
 	return ret;

 err:
 	free(keylst);
 	return ret;
 }

 #ifdef WITH_ANDROID
 static int erofs_droid_xattr_set_caps(struct erofs_inode *inode)
 {
 	const u64 capabilities = inode->capabilities;
 	char *kvbuf;
 	unsigned int len[2];
 	struct vfs_cap_data caps;
 	struct xattr_item *item;

 	if (!capabilities)
 		return 0;

 	len[0] = sizeof("capability") - 1;
 	len[1] = sizeof(caps);

 	kvbuf = malloc(len[0] + len[1]);
 	if (!kvbuf)
 		return -ENOMEM;

 	memcpy(kvbuf, "capability", len[0]);
 	caps.magic_etc = VFS_CAP_REVISION_2 | VFS_CAP_FLAGS_EFFECTIVE;
 	caps.data[0].permitted = (u32) capabilities;
 	caps.data[0].inheritable = 0;
 	caps.data[1].permitted = (u32) (capabilities >> 32);
 	caps.data[1].inheritable = 0;
 	memcpy(kvbuf + len[0], &caps, len[1]);

 	item = get_xattritem(EROFS_XATTR_INDEX_SECURITY, kvbuf, len);
 	if (IS_ERR(item))
 		return PTR_ERR(item);
 	if (!item)
 		return 0;

 	return erofs_xattr_add(&inode->i_xattrs, item);
 }
 #else
 static int erofs_droid_xattr_set_caps(struct erofs_inode *inode)
 {
 	return 0;
 }
 #endif

 int erofs_prepare_xattr_ibody(struct erofs_inode *inode)
 {
 	int ret;
 	struct inode_xattr_node *node;
 	struct list_head *ixattrs = &inode->i_xattrs;

 	/* check if xattr is disabled */
 	if (cfg.c_inline_xattr_tolerance < 0)
 		return 0;

 	ret = read_xattrs_from_file(inode->i_srcpath, inode->i_mode, ixattrs);
 	if (ret < 0)
 		return ret;

 	ret = erofs_droid_xattr_set_caps(inode);
 	if (ret < 0)
 		return ret;

 	if (list_empty(ixattrs))
 		return 0;

 	/* get xattr ibody size */
 	ret = sizeof(struct erofs_xattr_ibody_header);
 	list_for_each_entry(node, ixattrs, list) {
 		const struct xattr_item *item = node->item;

 		if (item->shared_xattr_id >= 0) {
 			ret += sizeof(__le32);
 			continue;
 		}
 		ret += sizeof(struct erofs_xattr_entry);
 		ret = EROFS_XATTR_ALIGN(ret + item->len[0] + item->len[1]);
 	}
 	inode->xattr_isize = ret;
 	return ret;
 }

 static int erofs_count_all_xattrs_from_path(const char *path)
 {
 	int ret;
 	DIR *_dir;
 	struct stat64 st;

 	_dir = opendir(path);
 	if (!_dir) {
 		erofs_err("failed to opendir at %s: %s",
 			  path, erofs_strerror(errno));
 		return -errno;
 	}

 	ret = 0;
 	while (1) {
 		struct dirent *dp;
 		char buf[PATH_MAX];

 		/*
 		 * set errno to 0 before calling readdir() in order to
 		 * distinguish end of stream and from an error.
 		 */
 		errno = 0;
 		dp = readdir(_dir);
 		if (!dp)
 			break;

 		if (is_dot_dotdot(dp->d_name) ||
 		    !strncmp(dp->d_name, "lost+found", strlen("lost+found")))
 			continue;

 		ret = snprintf(buf, PATH_MAX, "%s/%s", path, dp->d_name);

 		if (ret < 0 || ret >= PATH_MAX) {
 			/* ignore the too long path */
 			ret = -ENOMEM;
 			goto fail;
 		}

 		ret = lstat64(buf, &st);
 		if (ret) {
 			ret = -errno;
 			goto fail;
 		}

 		ret = read_xattrs_from_file(buf, st.st_mode, NULL);
 		if (ret)
 			goto fail;

 		if (!S_ISDIR(st.st_mode))
 			continue;

 		ret = erofs_count_all_xattrs_from_path(buf);
 		if (ret)
 			goto fail;
 	}

 	if (errno)
 		ret = -errno;

 fail:
 	closedir(_dir);
 	return ret;
 }

 static void erofs_cleanxattrs(bool sharedxattrs)
 {
 	unsigned int i;
 	struct xattr_item *item;
 	struct hlist_node *tmp;

 	hash_for_each_safe(ea_hashtable, i, tmp, item, node) {
 		if (sharedxattrs && item->shared_xattr_id >= 0)
 			continue;

 		hash_del(&item->node);
 		free(item);
 	}

 	if (sharedxattrs)
 		return;

 	shared_xattrs_size = shared_xattrs_count = 0;
 }

 static bool erofs_bh_flush_write_shared_xattrs(struct erofs_buffer_head *bh)
 {
 	void *buf = bh->fsprivate;
 	int err = dev_write(buf, erofs_btell(bh, false), shared_xattrs_size);

 	if (err)
 		return false;
 	free(buf);
 	return erofs_bh_flush_generic_end(bh);
 }

 static struct erofs_bhops erofs_write_shared_xattrs_bhops = {
 	.flush = erofs_bh_flush_write_shared_xattrs,
 };

 int erofs_build_shared_xattrs_from_path(const char *path)
 {
 	int ret;
 	struct erofs_buffer_head *bh;
 	struct inode_xattr_node *node, *n;
 	char *buf;
 	unsigned int p;
 	erofs_off_t off;

 	/* check if xattr or shared xattr is disabled */
 	if (cfg.c_inline_xattr_tolerance < 0 ||
 	    cfg.c_inline_xattr_tolerance == INT_MAX)
 		return 0;

 	if (shared_xattrs_size || shared_xattrs_count) {
 		DBG_BUGON(1);
 		return -EINVAL;
 	}

 	ret = erofs_count_all_xattrs_from_path(path);
 	if (ret)
 		return ret;

 	if (!shared_xattrs_size)
 		goto out;

 	buf = calloc(1, shared_xattrs_size);
 	if (!buf)
 		return -ENOMEM;

 	bh = erofs_balloc(XATTR, shared_xattrs_size, 0, 0);
 	if (IS_ERR(bh)) {
 		free(buf);
 		return PTR_ERR(bh);
 	}
 	bh->op = &erofs_skip_write_bhops;

 	erofs_mapbh(bh->block);
 	off = erofs_btell(bh, false);

 	sbi.xattr_blkaddr = off / EROFS_BLKSIZ;
 	off %= EROFS_BLKSIZ;
 	p = 0;

 	list_for_each_entry_safe(node, n, &shared_xattrs_list, list) {
 		struct xattr_item *const item = node->item;
 		const struct erofs_xattr_entry entry = {
 			.e_name_index = item->prefix,
 			.e_name_len = item->len[0],
 			.e_value_size = cpu_to_le16(item->len[1])
 		};

 		list_del(&node->list);

 		item->shared_xattr_id = (off + p) /
 			sizeof(struct erofs_xattr_entry);

 		memcpy(buf + p, &entry, sizeof(entry));
 		p += sizeof(struct erofs_xattr_entry);
 		memcpy(buf + p, item->kvbuf, item->len[0] + item->len[1]);
 		p = EROFS_XATTR_ALIGN(p + item->len[0] + item->len[1]);
 		free(node);
 	}
 	bh->fsprivate = buf;
 	bh->op = &erofs_write_shared_xattrs_bhops;
 out:
 	erofs_cleanxattrs(true);
 	return 0;
 }

 char *erofs_export_xattr_ibody(struct list_head *ixattrs, unsigned int size)
 {
 	struct inode_xattr_node *node, *n;
 	struct erofs_xattr_ibody_header *header;
 	LIST_HEAD(ilst);
 	unsigned int p;
 	char *buf = calloc(1, size);

 	if (!buf)
 		return ERR_PTR(-ENOMEM);

 	header = (struct erofs_xattr_ibody_header *)buf;
 	header->h_shared_count = 0;

 	p = sizeof(struct erofs_xattr_ibody_header);
 	list_for_each_entry_safe(node, n, ixattrs, list) {
 		struct xattr_item *const item = node->item;

 		list_del(&node->list);

 		/* move inline xattrs to the onstack list */
 		if (item->shared_xattr_id < 0) {
 			list_add(&node->list, &ilst);
 			continue;
 		}

 		*(__le32 *)(buf + p) = cpu_to_le32(item->shared_xattr_id);
 		p += sizeof(__le32);
 		++header->h_shared_count;
 		free(node);
 		put_xattritem(item);
 	}

 	list_for_each_entry_safe(node, n, &ilst, list) {
 		struct xattr_item *const item = node->item;
 		const struct erofs_xattr_entry entry = {
 			.e_name_index = item->prefix,
 			.e_name_len = item->len[0],
 			.e_value_size = cpu_to_le16(item->len[1])
 		};

 		memcpy(buf + p, &entry, sizeof(entry));
 		p += sizeof(struct erofs_xattr_entry);
 		memcpy(buf + p, item->kvbuf, item->len[0] + item->len[1]);
 		p = EROFS_XATTR_ALIGN(p + item->len[0] + item->len[1]);

 		list_del(&node->list);
 		free(node);
 		put_xattritem(item);
 	}
 	DBG_BUGON(p > size);
 	return buf;
 }
	// SPDX-License-Identifier: GPL-2.0+
	/*
	* erofs-utils/lib/xattr.c
	*
	* Originally contributed by an anonymous person,
	* heavily changed by Li Guifu <blucerlee@gmail.com>
	* and Gao Xiang <hsiangkao@aol.com>
	*/
	#define _GNU_SOURCE
	#include <stdlib.h>
	#include <sys/xattr.h>
	#ifdef HAVE_LINUX_XATTR_H
	#include <linux/xattr.h>
	#endif
	#include <sys/stat.h>
	#include <dirent.h>
	#include "erofs/print.h"
	#include "erofs/hashtable.h"
	#include "erofs/xattr.h"
	#include "erofs/cache.h"
	#include "erofs/io.h"

	#define EA_HASHTABLE_BITS 16

	struct xattr_item {
	const char *kvbuf;
	unsigned int hash[2], len[2], count;
	int shared_xattr_id;
	u8 prefix;
	struct hlist_node node;
	};

	struct inode_xattr_node {
	struct list_head list;
	struct xattr_item *item;
	};

	static DECLARE_HASHTABLE(ea_hashtable, EA_HASHTABLE_BITS);

	static LIST_HEAD(shared_xattrs_list);
	static unsigned int shared_xattrs_count, shared_xattrs_size;

	static struct xattr_prefix {
	const char *prefix;
	u16 prefix_len;
	} xattr_types[] = {
	[EROFS_XATTR_INDEX_USER] = {
	XATTR_USER_PREFIX,
	XATTR_USER_PREFIX_LEN
	}, [EROFS_XATTR_INDEX_POSIX_ACL_ACCESS] = {
	XATTR_NAME_POSIX_ACL_ACCESS,
	sizeof(XATTR_NAME_POSIX_ACL_ACCESS) - 1
	}, [EROFS_XATTR_INDEX_POSIX_ACL_DEFAULT] = {
	XATTR_NAME_POSIX_ACL_DEFAULT,
	sizeof(XATTR_NAME_POSIX_ACL_DEFAULT) - 1
	}, [EROFS_XATTR_INDEX_TRUSTED] = {
	XATTR_TRUSTED_PREFIX,
	XATTR_TRUSTED_PREFIX_LEN
	}, [EROFS_XATTR_INDEX_SECURITY] = {
	XATTR_SECURITY_PREFIX,
	XATTR_SECURITY_PREFIX_LEN
	}
	};

	static unsigned int BKDRHash(char *str, unsigned int len)
	{
	const unsigned int seed = 131313;
	unsigned int hash = 0;

	while (len) {
	hash = hash * seed + (*str++);
	--len;
	}
	return hash;
	}

	static unsigned int xattr_item_hash(u8 prefix, char *buf,
	unsigned int len[2], unsigned int hash[2])
	{
	hash[0] = BKDRHash(buf, len[0]); /* key */
	hash[1] = BKDRHash(buf + len[0], len[1]); /* value */

	return prefix ^ hash[0] ^ hash[1];
	}

	static unsigned int put_xattritem(struct xattr_item *item)
	{
	if (item->count > 1)
	return --item->count;
	free(item);
	return 0;
	}

	static struct xattr_item get_xattritem(u8 prefix, char kvbuf,
	unsigned int len[2])
	{
	struct xattr_item *item;
	unsigned int hash[2], hkey;

	hkey = xattr_item_hash(prefix, kvbuf, len, hash);

	hash_for_each_possible(ea_hashtable, item, node, hkey) {
	if (prefix == item->prefix &&
	item->len[0] == len[0] && item->len[1] == len[1] &&
	item->hash[0] == hash[0] && item->hash[1] == hash[1] &&
	!memcmp(kvbuf, item->kvbuf, len[0] + len[1])) {
	free(kvbuf);
	++item->count;
	return item;
	}
	}

	item = malloc(sizeof(*item));
	if (!item) {
	free(kvbuf);
	return ERR_PTR(-ENOMEM);
	}
	INIT_HLIST_NODE(&item->node);
	item->count = 1;
	item->kvbuf = kvbuf;
	item->len[0] = len[0];
	item->len[1] = len[1];
	item->hash[0] = hash[0];
	item->hash[1] = hash[1];
	item->shared_xattr_id = -1;
	item->prefix = prefix;
	hash_add(ea_hashtable, &item->node, hkey);
	return item;
	}

	static bool match_prefix(const char key, u8 index, u16 *len)
	{
	struct xattr_prefix *p;

	for (p = xattr_types; p < xattr_types + ARRAY_SIZE(xattr_types); ++p) {
	if (p->prefix && !strncmp(p->prefix, key, p->prefix_len)) {
	*len = p->prefix_len;
	*index = p - xattr_types;
	return true;
	}
	}
	return false;
	}

	static struct xattr_item parse_one_xattr(const char path, const char *key,
	unsigned int keylen)
	{
	ssize_t ret;
	u8 prefix;
	u16 prefixlen;
	unsigned int len[2];
	char *kvbuf;

	erofs_dbg("parse xattr [%s] of %s", path, key);

	if (!match_prefix(key, &prefix, &prefixlen))
	return ERR_PTR(-ENODATA);

	DBG_BUGON(keylen < prefixlen);

	/* determine length of the value */
	ret = lgetxattr(path, key, NULL, 0);
	if (ret < 0)
	return ERR_PTR(-errno);
	len[1] = ret;

	/* allocate key-value buffer */
	len[0] = keylen - prefixlen;

	kvbuf = malloc(len[0] + len[1]);
	if (!kvbuf)
	return ERR_PTR(-ENOMEM);
	memcpy(kvbuf, key + prefixlen, len[0]);
	if (len[1]) {
	/* copy value to buffer */
	ret = lgetxattr(path, key, kvbuf + len[0], len[1]);
	if (ret < 0) {
	free(kvbuf);
	return ERR_PTR(-errno);
	}
	if (len[1] != ret) {
	erofs_err("size of xattr value got changed just now (%u-> %ld)",
	len[1], (long)ret);
	len[1] = ret;
	}
	}
	return get_xattritem(prefix, kvbuf, len);
	}

	static struct xattr_item erofs_get_selabel_xattr(const char srcpath,
	mode_t mode)
	{
	#ifdef HAVE_LIBSELINUX
	if (cfg.sehnd) {
	char *secontext;
	int ret;
	unsigned int len[2];
	char kvbuf, fspath;

	#ifdef WITH_ANDROID
	if (cfg.mount_point)
	ret = asprintf(&fspath, "/%s/%s", cfg.mount_point,
	erofs_fspath(srcpath));
	else
	#endif
	ret = asprintf(&fspath, "/%s", erofs_fspath(srcpath));
	if (ret <= 0)
	return ERR_PTR(-ENOMEM);

	ret = selabel_lookup(cfg.sehnd, &secontext, fspath, mode);
	free(fspath);

	if (ret) {
	ret = -errno;
	if (ret != -ENOENT) {
	erofs_err("failed to lookup selabel for %s: %s",
	srcpath, erofs_strerror(ret));
	return ERR_PTR(ret);
	}
	/* secontext = "u:object_r:unlabeled:s0"; */
	return NULL;
	}

	len[0] = sizeof("selinux") - 1;
	len[1] = strlen(secontext);
	kvbuf = malloc(len[0] + len[1] + 1);
	if (!kvbuf) {
	freecon(secontext);
	return ERR_PTR(-ENOMEM);
	}
	sprintf(kvbuf, "selinux%s", secontext);
	freecon(secontext);
	return get_xattritem(EROFS_XATTR_INDEX_SECURITY, kvbuf, len);
	}
	#endif
	return NULL;
	}

	static int inode_xattr_add(struct list_head hlist, struct xattr_item item)
	{
	struct inode_xattr_node node = malloc(sizeof(node));

	if (!node)
	return -ENOMEM;
	init_list_head(&node->list);
	node->item = item;
	list_add(&node->list, hlist);
	return 0;
	}

	static int shared_xattr_add(struct xattr_item *item)
	{
	struct inode_xattr_node node = malloc(sizeof(node));

	if (!node)
	return -ENOMEM;

	init_list_head(&node->list);
	node->item = item;
	list_add(&node->list, &shared_xattrs_list);

	shared_xattrs_size += sizeof(struct erofs_xattr_entry);
	shared_xattrs_size = EROFS_XATTR_ALIGN(shared_xattrs_size +
	item->len[0] + item->len[1]);
	return ++shared_xattrs_count;
	}

	static int erofs_xattr_add(struct list_head ixattrs, struct xattr_item item)
	{
	if (ixattrs)
	return inode_xattr_add(ixattrs, item);

	if (item->count == cfg.c_inline_xattr_tolerance + 1) {
	int ret = shared_xattr_add(item);

	if (ret < 0)
	return ret;
	}
	return 0;
	}

	static bool erofs_is_skipped_xattr(const char *key)
	{
	#ifdef HAVE_LIBSELINUX
	/* if sehnd is valid, selabels will be overridden */
	if (cfg.sehnd && !strcmp(key, XATTR_SECURITY_PREFIX "selinux"))
	return true;
	#endif
	return false;
	}

	static int read_xattrs_from_file(const char *path, mode_t mode,
	struct list_head *ixattrs)
	{
	ssize_t kllen = llistxattr(path, NULL, 0);
	int ret;
	char keylst, key, *klend;
	unsigned int keylen;
	struct xattr_item *item;

	if (kllen < 0 && errno != ENODATA) {
	erofs_err("llistxattr to get the size of names for %s failed",
	path);
	return -errno;
	}

	ret = 0;
	if (kllen <= 1)
	goto out;

	keylst = malloc(kllen);
	if (!keylst)
	return -ENOMEM;

	/* copy the list of attribute keys to the buffer.*/
	kllen = llistxattr(path, keylst, kllen);
	if (kllen < 0) {
	erofs_err("llistxattr to get names for %s failed", path);
	ret = -errno;
	goto err;
	}

	/*
	* loop over the list of zero terminated strings with the
	* attribute keys. Use the remaining buffer length to determine
	* the end of the list.
	*/
	klend = keylst + kllen;
	ret = 0;

	for (key = keylst; key != klend; key += keylen + 1) {
	keylen = strlen(key);
	if (erofs_is_skipped_xattr(key))
	continue;

	item = parse_one_xattr(path, key, keylen);
	if (IS_ERR(item)) {
	ret = PTR_ERR(item);
	goto err;
	}

	ret = erofs_xattr_add(ixattrs, item);
	if (ret < 0)
	goto err;
	}
	free(keylst);

	out:
	/* if some selabel is avilable, need to add right now */
	item = erofs_get_selabel_xattr(path, mode);
	if (IS_ERR(item))
	return PTR_ERR(item);
	if (item)
	ret = erofs_xattr_add(ixattrs, item);
	return ret;

	err:
	free(keylst);
	return ret;
	}

	#ifdef WITH_ANDROID
	static int erofs_droid_xattr_set_caps(struct erofs_inode *inode)
	{
	const u64 capabilities = inode->capabilities;
	char *kvbuf;
	unsigned int len[2];
	struct vfs_cap_data caps;
	struct xattr_item *item;

	if (!capabilities)
	return 0;

	len[0] = sizeof("capability") - 1;
	len[1] = sizeof(caps);

	kvbuf = malloc(len[0] + len[1]);
	if (!kvbuf)
	return -ENOMEM;

	memcpy(kvbuf, "capability", len[0]);
	caps.magic_etc = VFS_CAP_REVISION_2 \| VFS_CAP_FLAGS_EFFECTIVE;
	caps.data[0].permitted = (u32) capabilities;
	caps.data[0].inheritable = 0;
	caps.data[1].permitted = (u32) (capabilities >> 32);
	caps.data[1].inheritable = 0;
	memcpy(kvbuf + len[0], &caps, len[1]);

	item = get_xattritem(EROFS_XATTR_INDEX_SECURITY, kvbuf, len);
	if (IS_ERR(item))
	return PTR_ERR(item);
	if (!item)
	return 0;

	return erofs_xattr_add(&inode->i_xattrs, item);
	}
	#else
	static int erofs_droid_xattr_set_caps(struct erofs_inode *inode)
	{
	return 0;
	}
	#endif

	int erofs_prepare_xattr_ibody(struct erofs_inode *inode)
	{
	int ret;
	struct inode_xattr_node *node;
	struct list_head *ixattrs = &inode->i_xattrs;

	/* check if xattr is disabled */
	if (cfg.c_inline_xattr_tolerance < 0)
	return 0;

	ret = read_xattrs_from_file(inode->i_srcpath, inode->i_mode, ixattrs);
	if (ret < 0)
	return ret;

	ret = erofs_droid_xattr_set_caps(inode);
	if (ret < 0)
	return ret;

	if (list_empty(ixattrs))
	return 0;

	/* get xattr ibody size */
	ret = sizeof(struct erofs_xattr_ibody_header);
	list_for_each_entry(node, ixattrs, list) {
	const struct xattr_item *item = node->item;

	if (item->shared_xattr_id >= 0) {
	ret += sizeof(__le32);
	continue;
	}
	ret += sizeof(struct erofs_xattr_entry);
	ret = EROFS_XATTR_ALIGN(ret + item->len[0] + item->len[1]);
	}
	inode->xattr_isize = ret;
	return ret;
	}

	static int erofs_count_all_xattrs_from_path(const char *path)
	{
	int ret;
	DIR *_dir;
	struct stat64 st;

	_dir = opendir(path);
	if (!_dir) {
	erofs_err("failed to opendir at %s: %s",
	path, erofs_strerror(errno));
	return -errno;
	}

	ret = 0;
	while (1) {
	struct dirent *dp;
	char buf[PATH_MAX];

	/*
	* set errno to 0 before calling readdir() in order to
	* distinguish end of stream and from an error.
	*/
	errno = 0;
	dp = readdir(_dir);
	if (!dp)
	break;

	if (is_dot_dotdot(dp->d_name) \|\|
	!strncmp(dp->d_name, "lost+found", strlen("lost+found")))
	continue;

	ret = snprintf(buf, PATH_MAX, "%s/%s", path, dp->d_name);

	if (ret < 0 \|\| ret >= PATH_MAX) {
	/* ignore the too long path */
	ret = -ENOMEM;
	goto fail;
	}

	ret = lstat64(buf, &st);
	if (ret) {
	ret = -errno;
	goto fail;
	}

	ret = read_xattrs_from_file(buf, st.st_mode, NULL);
	if (ret)
	goto fail;

	if (!S_ISDIR(st.st_mode))
	continue;

	ret = erofs_count_all_xattrs_from_path(buf);
	if (ret)
	goto fail;
	}

	if (errno)
	ret = -errno;

	fail:
	closedir(_dir);
	return ret;
	}

	static void erofs_cleanxattrs(bool sharedxattrs)
	{
	unsigned int i;
	struct xattr_item *item;
	struct hlist_node *tmp;

	hash_for_each_safe(ea_hashtable, i, tmp, item, node) {
	if (sharedxattrs && item->shared_xattr_id >= 0)
	continue;

	hash_del(&item->node);
	free(item);
	}

	if (sharedxattrs)
	return;

	shared_xattrs_size = shared_xattrs_count = 0;
	}

	static bool erofs_bh_flush_write_shared_xattrs(struct erofs_buffer_head *bh)
	{
	void *buf = bh->fsprivate;
	int err = dev_write(buf, erofs_btell(bh, false), shared_xattrs_size);

	if (err)
	return false;
	free(buf);
	return erofs_bh_flush_generic_end(bh);
	}

	static struct erofs_bhops erofs_write_shared_xattrs_bhops = {
	.flush = erofs_bh_flush_write_shared_xattrs,
	};

	int erofs_build_shared_xattrs_from_path(const char *path)
	{
	int ret;
	struct erofs_buffer_head *bh;
	struct inode_xattr_node node, n;
	char *buf;
	unsigned int p;
	erofs_off_t off;

	/* check if xattr or shared xattr is disabled */
	if (cfg.c_inline_xattr_tolerance < 0 \|\|
	cfg.c_inline_xattr_tolerance == INT_MAX)
	return 0;

	if (shared_xattrs_size \|\| shared_xattrs_count) {
	DBG_BUGON(1);
	return -EINVAL;
	}

	ret = erofs_count_all_xattrs_from_path(path);
	if (ret)
	return ret;

	if (!shared_xattrs_size)
	goto out;

	buf = calloc(1, shared_xattrs_size);
	if (!buf)
	return -ENOMEM;

	bh = erofs_balloc(XATTR, shared_xattrs_size, 0, 0);
	if (IS_ERR(bh)) {
	free(buf);
	return PTR_ERR(bh);
	}
	bh->op = &erofs_skip_write_bhops;

	erofs_mapbh(bh->block);
	off = erofs_btell(bh, false);

	sbi.xattr_blkaddr = off / EROFS_BLKSIZ;
	off %= EROFS_BLKSIZ;
	p = 0;

	list_for_each_entry_safe(node, n, &shared_xattrs_list, list) {
	struct xattr_item *const item = node->item;
	const struct erofs_xattr_entry entry = {
	.e_name_index = item->prefix,
	.e_name_len = item->len[0],
	.e_value_size = cpu_to_le16(item->len[1])
	};

	list_del(&node->list);

	item->shared_xattr_id = (off + p) /
	sizeof(struct erofs_xattr_entry);

	memcpy(buf + p, &entry, sizeof(entry));
	p += sizeof(struct erofs_xattr_entry);
	memcpy(buf + p, item->kvbuf, item->len[0] + item->len[1]);
	p = EROFS_XATTR_ALIGN(p + item->len[0] + item->len[1]);
	free(node);
	}
	bh->fsprivate = buf;
	bh->op = &erofs_write_shared_xattrs_bhops;
	out:
	erofs_cleanxattrs(true);
	return 0;
	}

	char erofs_export_xattr_ibody(struct list_head ixattrs, unsigned int size)
	{
	struct inode_xattr_node node, n;
	struct erofs_xattr_ibody_header *header;
	LIST_HEAD(ilst);
	unsigned int p;
	char *buf = calloc(1, size);

	if (!buf)
	return ERR_PTR(-ENOMEM);

	header = (struct erofs_xattr_ibody_header *)buf;
	header->h_shared_count = 0;

	p = sizeof(struct erofs_xattr_ibody_header);
	list_for_each_entry_safe(node, n, ixattrs, list) {
	struct xattr_item *const item = node->item;

	list_del(&node->list);

	/* move inline xattrs to the onstack list */
	if (item->shared_xattr_id < 0) {
	list_add(&node->list, &ilst);
	continue;
	}

	(__le32 )(buf + p) = cpu_to_le32(item->shared_xattr_id);
	p += sizeof(__le32);
	++header->h_shared_count;
	free(node);
	put_xattritem(item);
	}

	list_for_each_entry_safe(node, n, &ilst, list) {
	struct xattr_item *const item = node->item;
	const struct erofs_xattr_entry entry = {
	.e_name_index = item->prefix,
	.e_name_len = item->len[0],
	.e_value_size = cpu_to_le16(item->len[1])
	};

	memcpy(buf + p, &entry, sizeof(entry));
	p += sizeof(struct erofs_xattr_entry);
	memcpy(buf + p, item->kvbuf, item->len[0] + item->len[1]);
	p = EROFS_XATTR_ALIGN(p + item->len[0] + item->len[1]);

	list_del(&node->list);
	free(node);
	put_xattritem(item);
	}
	DBG_BUGON(p > size);
	return buf;
	}