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

[Gao Xiang]

The trailing '\n' shouldn't be part of backend.

Fixes: 5d3efc9babf3 ("erofs-utils: mount: enable autoclear for NBD devices")
Cc: Chengyu Zhu <hud...@cyzhu.com>
Signed-off-by: Gao Xiang <hsiang...@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