[PATCH] erofs-utils: lib: avoid trailing '\n' in erofs_nbd_get_identifier()

[hudsonZhu]

I have tested this patch and it can fix the autoclear issue when executing `mount.erofs -t erofs.nbd erofs.img /mnt`.

Nice patch, Xiang.

Thanks,
Chengyu Zhu

> 2025年9月5日 11:39，Gao Xiang <hsiangkao at linux.alibaba.com> 写道：
> 
> The trailing '\n' shouldn't be part of backend.
> 
> Fixes: 5d3efc9babf3 ("erofs-utils: mount: enable autoclear for NBD devices")
> Cc: Chengyu Zhu <hudson at cyzhu.com>
> Signed-off-by: Gao Xiang <hsiangkao at linux.alibaba.com>
> ---
> lib/backends/nbd.c | 21 +++++++++++++++------
> mount/main.c       | 20 +++++---------------
> 2 files changed, 20 insertions(+), 21 deletions(-)
> 
> diff --git a/lib/backends/nbd.c b/lib/backends/nbd.c
> index b9535dc..2e54814 100644
> --- a/lib/backends/nbd.c
> +++ b/lib/backends/nbd.c
> @@ -183,15 +183,24 @@ char *erofs_nbd_get_identifier(int nbdnum)
> 
> 	(void)snprintf(s, sizeof(s), "/sys/block/nbd%d/backend", nbdnum);
> 	f = fopen(s, "r");
> -	if (!f)
> +	if (!f) {
> +		if (errno == ENOENT)
> +			return NULL;
> 		return ERR_PTR(-errno);
> -
> -	if (getline(&line, &n, f) < 0)
> +	}
> +	err = getline(&line, &n, f);
> +	if (err < 0)
> 		err = -errno;
> -	else
> -		err = 0;
> 	fclose(f);
> -	return err ? ERR_PTR(err) : line;
> +	if (err < 0)
> +		return ERR_PTR(err);
> +	if (!err) {
> +		free(line);
> +		return NULL;
> +	}
> +	if (line[err - 1] == '\n')
> +		line[err - 1] = '\0';
> +	return line;
> }
> 
> int erofs_nbd_get_index_from_minor(int minor)
> diff --git a/mount/main.c b/mount/main.c
> index 149bb53..2826dac 100644
> --- a/mount/main.c
> +++ b/mount/main.c
> @@ -356,10 +356,7 @@ static int erofsmount_nbd_fix_backend_linkage(int num, char **recp)
> 	int err;
> 
> 	newrecp = erofs_nbd_get_identifier(num);
> -	if (!IS_ERR(newrecp)) {
> -		err = strlen(newrecp);
> -		if (newrecp[err - 1] == '\n')
> -			newrecp[err - 1] = '\0';
> +	if (!IS_ERR(newrecp) && newrecp) {
> 		err = strcmp(newrecp, *recp) ? -EFAULT : 0;
> 		free(newrecp);
> 		return err;
> @@ -461,16 +458,11 @@ static int erofsmount_reattach(const char *target)
> 	if (nbdnum < 0)
> 		return nbdnum;
> 	identifier = erofs_nbd_get_identifier(nbdnum);
> -	if (IS_ERR(identifier))
> +	if (IS_ERR(identifier)) {
> +		identifier = NULL;
> +	} else if (identifier && *identifier == '\0') {
> +		free(identifier);
> 		identifier = NULL;
> -	else if (identifier) {
> -		n = strlen(identifier);
> -		if (__erofs_unlikely(!n)) {
> -			free(identifier);
> -			identifier = NULL;
> -		} else if (identifier[n - 1] == '\n') {
> -			identifier[n - 1] = '\0';
> -		}
> 	}
> 
> 	if (!identifier &&
> @@ -596,8 +588,6 @@ static int erofsmount_nbd(const char *source, const char *mountpoint,
> 
> 		if (!err && is_netlink) {
> 			id = erofs_nbd_get_identifier(num);
> -			if (id == ERR_PTR(-ENOENT))
> -				id = NULL;
> 
> 			err = IS_ERR(id) ? PTR_ERR(id) :
> 				erofs_nbd_nl_reconfigure(num, id, true);
> -- 
> 2.43.5