| Message ID | 20180724172638.760873-1-lkundrak@v3.sk |
|---|---|
| State | Accepted, archived |
| Delegated to: | stephen hemminger |
| Headers | show |
| Series | [iproute] lib/namespace: avoid double-mounting a /sys | expand |
On Tue, 24 Jul 2018 19:26:38 +0200 Lubomir Rintel <lkundrak@v3.sk> wrote: > This partly reverts 8f0807023d067e2bb585a2ae8da93e59689d10f1, 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> Makes sens applied.
diff --git a/lib/namespace.c b/lib/namespace.c index 43e0fe34..06ae0a48 100644 --- a/lib/namespace.c +++ b/lib/namespace.c @@ -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) {
This partly reverts 8f0807023d067e2bb585a2ae8da93e59689d10f1, 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> --- lib/namespace.c | 20 +++++++------------- 1 file changed, 7 insertions(+), 13 deletions(-)