It might not be feasible for users to start passt-repair after passt
is started, on a migration target, but before the migration process
starts.

For instance, with libvirt, the guest domain (and, hence, passt) is
started on the target as part of the migration process. At least for
the moment being, there's no hook a libvirt user (including KubeVirt)
can use to start passt-repair before the migration starts.

Add a directory watch using inotify: if PATH is a directory, instead
of connecting to it, we'll watch for a .repair socket file to appear
in it, and then attempt to connect to that socket.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

Here are a bunch of workarounds and a couple of fixes for libvirt
usage which are rather hard to split into single logical patches
as there appear to be some obscure dependencies between some of them:

- passt-repair needs to have an exec_type typeattribute (otherwise
  the policy for lsmd(1) causes a violation on getattr on its
  executable) file, and that typeattribute just happened to be there
  for passt as a result of init_daemon_domain(), but passt-repair
  isn't a daemon, so we need an explicit corecmd_executable_file()

- passt-repair needs a workaround, which I'll revisit once
  https://github.com/fedora-selinux/selinux-policy/issues/2579 is
  solved, for usage with libvirt: allow it to use qemu_var_run_t
  and virt_var_run_t sockets

- add 'bpf' and 'dac_read_search' capabilities for passt-repair:
  they are needed (for whatever reason I didn't investigate) to
  actually receive socket files via SCM_RIGHTS

- passt needs further workarounds in the sense of
  https://github.com/fedora-selinux/selinux-policy/issues/2579:
  allow it to use map and use svirt_tmpfs_t (not just svirt_image_t):
  it depends on where the libvirt guest image is

- ...it also needs to map /dev/null if <access mode='shared'/> is
  enabled in libvirt's XML for the memoryBacking object, for
  vhost-user operation

- and 'ioctl' on the TCP socket appears to be actually needed, on top
  of 'getattr', to dump some socket parameters

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

A privileged helper to set/clear TCP_REPAIR on sockets on behalf of
passt. Not used yet.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>