findmnt: use tree output in more cases

It seems that we can create the tree also if output is restricted by
fstype or options filter, for example

	$ findmnt -t cgroups

Signed-off-by: Karel Zak <kzak@redhat.com>
Revert "unshare: support the switching of namespaces"

The functionality will be replaced with nsenter from Eric W.
Biederman.

This reverts commit 4bbe8099390d528018890efa914e268de3c4b44b.
nsenter: new command (light wrapper around setns)

Inspired by unshare, nsenter is a simple wrapper around setns that
allows running a new process in the context of an existing process.

Full paths may be specified to the namespace arguments so that
namespace file descriptors may be used wherever they reside in the
filesystem.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
unshare: Add support for the pid and user namespaces

- Update the unshare application to support the pid and user namespaces.
- Update the man page for the new options
- Fix typo in the man page where UTS was spelled UTC.
- Remove the vestigal support for running a suid unshare.
  After unsharing a user namespace setuid(getuid()) won't work because
  no uid or gid mappings have been specified yet. So it is just easier not
  to have any support for running suid.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
nsenter: Enhance waiting for a child process

In the case of a pid namespace we need to fork a child process instead
of calling exec.  Move all of that logic out of line into a function
continue_as_child, making the logic of the primary case easier to
understand.

Update the logic for waiting for a child process to suspend ourselves
when the child processes suspends and to continue the child process
when we are unsuspsended.  This supports the bash suspend command and
various editors that suspend themselves.

If the child process exits with a signal update the logic to run
kill(getpid(), WTERMSIG(status)) so the caller sees the same exit code
that nsenter observed.

There will always be permission to send signals to our children and
the tty is not changing so there is no need for the intermediate
process to forward signals to it's child.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
nsenter: Properly spell significant in a comment.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
nsenter: Add const to declarations where possible.

Make it clear where functions do not modify their arguments.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
nsenter: Replace a bare strtoul with strtoul_or_err

This is shorter code and makes things a bit clearer and less
error prone if anyone happens to copy the code.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
unshare,nsenter: Move the old libc handling into a common header namespace.h

Move the defitions of CLONE_NEWNS, CLONE_NEWUTS, CLONE_NEWIPC,
CLONE_NEWNET, CLONE_NEWUSER, CLONE_NEWPID into namespace.h in case
sched.h does not provide those definitions.  Are there systems
around that are old enough that still need this?

Move the definitions of unshare() and setns() into namespace.h
for supporting old versions of libc that does not provice these.
I have tested this support with setns as I still have systems
old enough that glibc does not wrap setns.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
nsenter: improve optional args in usage() and man page

Signed-off-by: Karel Zak <kzak@redhat.com>