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core/mount: pass "-c" flag to /bin/umount (#6093)

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"-c", which is short for "--no-canonicalize", tells /bin/umount
that the path name is canonical (no .. or symlinks etc).

systemd always uses a canonical name, so this flag is appropriate
for systemd to use.
Knowing that the path is canonical allows umount to avoid
some calls to lstat() on the path.

From v2.30 "-c" goes further and causes umount to avoid all
attempts to 'lstat()' (or similar) the path.  This is important
when automatically unmounting a filesystem, as lstat() can
hang indefinitely in some cases such as when an NFS server
is not accessible.

"-c" has been supported since util-linux 2.17 which is before the
earliest version supported by systemd.
So "-c" is safe to use now, and once util-linux v2.30 is in use,
it will allow mounts from non-responsive NFS servers to be
unmounted.
This commit is contained in:
NeilBrown 2017-06-07 22:28:23 +10:00 committed by Lennart Poettering
parent 3bd82598a1
commit 83897d5470
1 changed files with 1 additions and 1 deletions
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2
src/core/mount.c
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@ -886,7 +886,7 @@ static void mount_enter_unmounting(Mount *m) {
m->control_command_id = MOUNT_EXEC_UNMOUNT;
m->control_command = m->exec_command + MOUNT_EXEC_UNMOUNT;
r = exec_command_set(m->control_command, UMOUNT_PATH, m->where, NULL);
r = exec_command_set(m->control_command, UMOUNT_PATH, m->where, "-c", NULL);
if (r >= 0 && m->lazy_unmount)
r = exec_command_append(m->control_command, "-l", NULL);
if (r >= 0 && m->force_unmount)