Re: [PATCH 07/13] erofs-utils: lib: add erofs_read_xattrs_from_disk() helper

[Gao Xiang]

On 2023/8/14 11:42, Jingbo Xu wrote:

Add erofs_read_xattrs_from_disk() helper to read extended attributes
from disk.

Signed-off-by: Jingbo Xu <jeffl...@linux.alibaba.com>
---
  include/erofs/xattr.h |  1 +
  lib/xattr.c           | 76 +++++++++++++++++++++++++++++++++++++++++++
  2 files changed, 77 insertions(+)

diff --git a/include/erofs/xattr.h b/include/erofs/xattr.h
index dc27cf6..634daf9 100644
--- a/include/erofs/xattr.h
+++ b/include/erofs/xattr.h
@@ -85,6 +85,7 @@ int erofs_xattr_write_name_prefixes(struct erofs_sb_info 
*sbi, FILE *f);

int erofs_setxattr(struct erofs_inode *inode, char *key,

                   const void *value, size_t size);
+int erofs_read_xattrs_from_disk(struct erofs_inode *inode);

#ifdef __cplusplus

  }
diff --git a/lib/xattr.c b/lib/xattr.c
index 12f580e..8d8f9f0 100644
--- a/lib/xattr.c
+++ b/lib/xattr.c
@@ -493,6 +493,82 @@ int erofs_scan_file_xattrs(struct erofs_inode *inode)
        return erofs_droid_xattr_set_caps(inode);
  }

+static struct xattr_item *erofs_read_xattr_from_disk(struct erofs_inode *inode,

+                                                    char *key)
+{
+       ssize_t ret;
+       u8 prefix;
+       u16 prefixlen;
+       unsigned int len[2];
+       char *kvbuf;
+
+       if (!match_prefix(key, &prefix, &prefixlen))
+               return ERR_PTR(-ENODATA);
+
+       ret = erofs_getxattr(inode, key, NULL, 0);
+       if (ret < 0)
+               return ERR_PTR(-errno);
+
+       /* allocate key-value buffer */
+       len[0] = strlen(key) - prefixlen;
+       len[1] = ret;
+       kvbuf = malloc(len[0] + len[1]);
+       if (!kvbuf)
+               return ERR_PTR(-ENOMEM);
+       memcpy(kvbuf, key + prefixlen, len[0]);
+       if (len[1]) {
+               ret = erofs_getxattr(inode, key, kvbuf + len[0], len[1]);
+               if (ret < 0) {
+                       free(kvbuf);
+                       return ERR_PTR(-errno);
+               }
+               if (ret != len[1]) {
+                       erofs_err("size of xattr value got changed just now (%u-> 
%ld)",
+                                 len[1], (long)ret);
+                       len[1] = ret;
+               }

Can this actually happen? Maybe just:
                DBG_BUGON(ret != len[1]);

Thanks,
Gao Xiang