[PATCH v2] vfs: use "none" if mount source is empty string

From: Yecheng Fu <cofyc.jackson@gmail.com>
To: Alexander Viro <viro@zeniv.linux.org.uk>,
	Matthew Wilcox <willy@infradead.org>
Cc: linux-fsdevel@vger.kernel.org, Karel Zak <kzak@redhat.com>,
	Yecheng Fu <cofyc.jackson@gmail.com>
Subject: [PATCH v2] vfs: use "none" if mount source is empty string
Date: Thu, 19 Apr 2018 11:47:21 +0800	[thread overview]
Message-ID: <1524109641-45617-1-git-send-email-cofyc.jackson@gmail.com> (raw)

`libmount` from util-linux and many softwares in userspace (e.g.
kubelet) did not expect empty string as mount source:

```
$ mount -t tmpfs "" /mnt/tmpfs
$ findmnt /mnt/tmpfs
findmnt: /proc/self/mountinfo: parse error at line 51
$ cat /proc/self/mountinfo | grep -P '\/mnt\/tmpfs'
74 25 0:59 / /mnt/tmpfs rw,relatime shared:38 - tmpfs  rw
$ cat /proc/self/mounts | grep -P '\/mnt\/tmpfs'
 /mnt/tmpfs tmpfs rw,relatime 0 0
```

`source` field in mounts/mountinfo is empty, which breaks a lot of
mounts/mountinfo parsers.

This fixes issues in parsing when user uses empty string as mount
source.

Cc: Karel Zak <kzak@redhat.com>
Signed-off-by: Yecheng Fu <cofyc.jackson@gmail.com>
---

PATCH v2 updates `show_vfsstat()` too.

 fs/proc_namespace.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/fs/proc_namespace.c b/fs/proc_namespace.c
index 3f1190d..24591b8 100644
--- a/fs/proc_namespace.c
+++ b/fs/proc_namespace.c
@@ -104,7 +104,7 @@ static int show_vfsmnt(struct seq_file *m, struct vfsmount *mnt)
 		if (err)
 			goto out;
 	} else {
-		mangle(m, r->mnt_devname ? r->mnt_devname : "none");
+		mangle(m, (r->mnt_devname && r->mnt_devname[0] != '\0') ? r->mnt_devname : "none");
 	}
 	seq_putc(m, ' ');
 	/* mountpoints outside of chroot jail will give SEQ_SKIP on this */
@@ -174,7 +174,7 @@ static int show_mountinfo(struct seq_file *m, struct vfsmount *mnt)
 		if (err)
 			goto out;
 	} else {
-		mangle(m, r->mnt_devname ? r->mnt_devname : "none");
+		mangle(m, (r->mnt_devname && r->mnt_devname[0] != '\0') ? r->mnt_devname : "none");
 	}
 	seq_puts(m, sb->s_flags & MS_RDONLY ? " ro" : " rw");
 	err = show_sb_opts(m, sb);
@@ -202,7 +202,7 @@ static int show_vfsstat(struct seq_file *m, struct vfsmount *mnt)
 		if (err)
 			goto out;
 	} else {
-		if (r->mnt_devname) {
+		if (r->mnt_devname && r->mnt_devname[0] != '\0') {
 			seq_puts(m, "device ");
 			mangle(m, r->mnt_devname);
 		} else
-- 
Yecheng Fu
