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lib/namespace: avoid double-mounting a /sys

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This partly reverts 8f0807023d, bringing
back the umount(/sys) attempt.

In a LXC container we're unable to umount the sysfs instance, nor mount
a read-write one. We still are able to create a new read-only instance.

Nevertheless, it still makes sense to attempt the umount() even though
the sysfs is mounted read-only. Otherwise we may end up attempting to
mount a sysfs with the same flags as is already mounted, resulting in
an EBUSY error (meaning "Already mounted").

Perhaps this is not a very likely scenario in real world, but we hit
it in NetworkManager test suite and makes netns_switch() somewhat more
robust. It also fixes the case, when /sys wasn't mounted at all.

Signed-off-by: Lubomir Rintel <lkundrak@v3.sk>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
This commit is contained in:
Lubomir Rintel 2018-07-24 19:26:38 +02:00 committed by Stephen Hemminger
parent c8f7a754ed
commit 3655f788d3
1 changed files with 7 additions and 13 deletions
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20
lib/namespace.c
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@ -82,19 +82,13 @@ int netns_switch(char *name)
/* Mount a version of /sys that describes the network namespace */
if (statvfs("/sys", &fsstat) < 0) {
fprintf(stderr, "could not stat /sys (not mounted?): %s\n",strerror(errno));
return -1;
}
if (fsstat.f_flag & ST_RDONLY) {
/* If /sys is not writable (e.g. in a container), we can't
* unmount the old /sys instance, but we can still mount a new
* read-only instance over it. */
mountflags = MS_RDONLY;
} else {
if (umount2("/sys", MNT_DETACH) < 0) {
fprintf(stderr, "umount of /sys failed: %s\n", strerror(errno));
return -1;
if (umount2("/sys", MNT_DETACH) < 0) {
/* If this fails, perhaps there wasn't a sysfs instance mounted. Good. */
if (statvfs("/sys", &fsstat) == 0) {
/* We couldn't umount the sysfs, we'll attempt to overlay it.
* A read-only instance can't be shadowed with a read-write one. */
if (fsstat.f_flag & ST_RDONLY)
mountflags = MS_RDONLY;
}
}
if (mount(name, "/sys", "sysfs", mountflags, NULL) < 0) {