erofs: add helpers to load long xattr name prefixes

Long xattr name prefixes will be scanned upon mounting and the in-memory
long xattr name prefix array will be initialized accordingly.
Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Acked-by: Chao Yu <chao@kernel.org>
Link: https://lore.kernel.org/r/20230407141710.113882-6-jefflexu@linux.alibaba.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/erofs/internal.h

@@ -117,6 +117,11 @@ struct erofs_fscache {
 	char *name;
 };
 
+struct erofs_xattr_prefix_item {
+	struct erofs_xattr_long_prefix *prefix;
+	u8 infix_len;
+};
+
 struct erofs_sb_info {
 	struct erofs_mount_opts opt;	/* options */
 #ifdef CONFIG_EROFS_FS_ZIP
@@ -145,6 +150,9 @@ struct erofs_sb_info {
 	u32 meta_blkaddr;
 #ifdef CONFIG_EROFS_FS_XATTR
 	u32 xattr_blkaddr;
+	u32 xattr_prefix_start;
+	u8 xattr_prefix_count;
+	struct erofs_xattr_prefix_item *xattr_prefixes;
 #endif
 	u16 device_id_mask;	/* valid bits of device id to be used */
 
@@ -440,6 +448,8 @@ extern const struct iomap_ops z_erofs_iomap_report_ops;
 #define EROFS_REG_COOKIE_SHARE		0x0001
 #define EROFS_REG_COOKIE_NEED_NOEXIST	0x0002
 
+void *erofs_read_metadata(struct super_block *sb, struct erofs_buf *buf,
+			  erofs_off_t *offset, int *lengthp);
 void erofs_unmap_metabuf(struct erofs_buf *buf);
 void erofs_put_metabuf(struct erofs_buf *buf);
 void *erofs_bread(struct erofs_buf *buf, erofs_blk_t blkaddr,

fs/erofs/super.c

@@ -126,9 +126,8 @@ static bool check_layout_compatibility(struct super_block *sb,
 	return true;
 }
 
-#ifdef CONFIG_EROFS_FS_ZIP
 /* read variable-sized metadata, offset will be aligned by 4-byte */
-static void *erofs_read_metadata(struct super_block *sb, struct erofs_buf *buf,
+void *erofs_read_metadata(struct super_block *sb, struct erofs_buf *buf,
 			  erofs_off_t *offset, int *lengthp)
 {
 	u8 *buffer, *ptr;
@@ -162,6 +161,7 @@ static void *erofs_read_metadata(struct super_block *sb, struct erofs_buf *buf,
 	return buffer;
 }
 
+#ifdef CONFIG_EROFS_FS_ZIP
 static int erofs_load_compr_cfgs(struct super_block *sb,
 				 struct erofs_super_block *dsb)
 {

fs/erofs/xattr.c

@@ -610,6 +610,62 @@ ssize_t erofs_listxattr(struct dentry *dentry,
 	return ret;
 }
 
+void erofs_xattr_prefixes_cleanup(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	int i;
+
+	if (sbi->xattr_prefixes) {
+		for (i = 0; i < sbi->xattr_prefix_count; i++)
+			kfree(sbi->xattr_prefixes[i].prefix);
+		kfree(sbi->xattr_prefixes);
+		sbi->xattr_prefixes = NULL;
+	}
+}
+
+int erofs_xattr_prefixes_init(struct super_block *sb)
+{
+	struct erofs_sb_info *sbi = EROFS_SB(sb);
+	struct erofs_buf buf = __EROFS_BUF_INITIALIZER;
+	erofs_off_t pos = (erofs_off_t)sbi->xattr_prefix_start << 2;
+	struct erofs_xattr_prefix_item *pfs;
+	int ret = 0, i, len;
+
+	if (!sbi->xattr_prefix_count)
+		return 0;
+
+	pfs = kzalloc(sbi->xattr_prefix_count * sizeof(*pfs), GFP_KERNEL);
+	if (!pfs)
+		return -ENOMEM;
+
+	if (erofs_sb_has_fragments(sbi))
+		buf.inode = sbi->packed_inode;
+	else
+		erofs_init_metabuf(&buf, sb);
+
+	for (i = 0; i < sbi->xattr_prefix_count; i++) {
+		void *ptr = erofs_read_metadata(sb, &buf, &pos, &len);
+
+		if (IS_ERR(ptr)) {
+			ret = PTR_ERR(ptr);
+			break;
+		} else if (len < sizeof(*pfs->prefix) ||
+			   len > EROFS_NAME_LEN + sizeof(*pfs->prefix)) {
+			kfree(ptr);
+			ret = -EFSCORRUPTED;
+			break;
+		}
+		pfs[i].prefix = ptr;
+		pfs[i].infix_len = len - sizeof(struct erofs_xattr_long_prefix);
+	}
+
+	erofs_put_metabuf(&buf);
+	sbi->xattr_prefixes = pfs;
+	if (ret)
+		erofs_xattr_prefixes_cleanup(sb);
+	return ret;
+}
+
 #ifdef CONFIG_EROFS_FS_POSIX_ACL
 struct posix_acl *erofs_get_acl(struct inode *inode, int type, bool rcu)
 {

fs/erofs/xattr.h

@@ -40,9 +40,13 @@ static inline const struct xattr_handler *erofs_xattr_handler(unsigned int idx)
 
 extern const struct xattr_handler *erofs_xattr_handlers[];
 
+int erofs_xattr_prefixes_init(struct super_block *sb);
+void erofs_xattr_prefixes_cleanup(struct super_block *sb);
 int erofs_getxattr(struct inode *, int, const char *, void *, size_t);
 ssize_t erofs_listxattr(struct dentry *, char *, size_t);
 #else
+static inline int erofs_xattr_prefixes_init(struct super_block *sb) { return 0; }
+static inline void erofs_xattr_prefixes_cleanup(struct super_block *sb) {}
 static inline int erofs_getxattr(struct inode *inode, int index,
 				 const char *name, void *buffer,
 				 size_t buffer_size)