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

[Gao Xiang <hsiangkao@linux.alibaba.com>]

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 <jefflexu@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