unshare: add --propagation, use MS_PRIVATE by default

After "unshare --mount" users assume that mount operations within the
new namespaces are unshared (invisible for the rest of the system).

Unfortunately, this is not true and the behavior depends on the
current mount propagation setting. The kernel default is "private",
but for example systemd based distros use "shared". The solution is to
use (for example) "mount --make-private" after unshare(1).

I have been requested many times to provide less fragile and more
unified unshared mount setting *by default* to make things user
friendly.

The patch forces unshare(1) to explicitly use MS_REC|MS_PRIVATE for all
tree by default.

We can use something less (e.g MS_SLAVE), but "private" is the kernel
default, so for many users this change (feature) will be invisible.

This feature is possible to disable by "--propagation unchanged" or it's
possible to specify another propagation flag, supported are:

	<slave|shared|private|unchanged>

Acked-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Karel Zak <kzak@redhat.com>

0 files changed, 0 insertions, 0 deletions