Add separate list for slave tty fds on restore v2

When we will be restoring ttys we need that restore
procedure for master peers will be yielded earlier
than for slave peers due to ttys specifics. With this
commit we introduce @tty_slaves list which will allow
us to order tty file restore procesure.

Because we need to fetch which list to be used depending
on tty type this patch extend select_ps_list with fdinfo_list_entry
parameter.

v2 (by xemul@):
 - make sure the epoll list is still last

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
tty: Add checkpoint/restore for unix terminals v6

Usually the PTYs represent a pair of links -- master peer and slave
peer. Master peer must be opened before slave. Internally, when kernel
creates master peer it also generates a slave interface in a form of
/dev/pts/N, where N is that named pty "index". Master/slave connection
unambiguously identified by this index.

Still, one master can carry multiple slaves -- for example a user opens
one master via /dev/ptmx and appropriate /dev/pts/N in sequence.
The result will be the following

master
`- slave 1
`- slave 2

both slave will have same master index but different file descriptors.
Still inside the kernel pty parameters are same for both slaves. Thus
only one slave parameters should be restored, there is no need to carry
all parameters for every slave peer we've found.

Not yet addressed problems:

- At moment of restore the master peer might be already closed for
  any reason so to resolve such problem we need to open a fake master
  peer with proper index and hook a slave on it, then we close
  master peer.

- Need to figure out how to deal with ttys which have some
  data in buffers not yet flushed, at moment this data will
  be simply lost during c/r

- Need to restore control terminals

- Need to fetch tty flags such as exclusive/packet-mode,
  this can't be done without kernel patching

[ avagin@:
   - ideas on contol terminals restore
   - overall code redesign and simplification
]

v4:
 - drop redundant pid from dump_chrdev
 - make sure optional fown is passed on regular ptys
 - add a comments about zeroifying termios
 - get rid of redundant empty line in files.c

v5 (by avagin@):
 - complete rework of tty image format, now we have
   two files -- tty.img and tty-info.img. The idea
   behind to reduce data being stored.

v6 (by xemul@):
 - packet mode should be set to true in image,
   until properly fetched from the kernel
 - verify image data on retrieval

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
CC: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
tty: Add show method

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
check: Add check_tty

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
tty: Add restoration of controlling terminal v4

The idea behind is pretty simple -- once we find
that there is a controlling terminal present we
do call ioctl on appropriate /dev/pts/N.

This is done in a bit unusuall manner. When we
find that there is a controling terminal present
we do create an additional FdinfoEntry for it
with object id taken from existing master peer.

The file engine stack this new FdinfoEntry on
fd_info_head head list. Thus we will have at
least two entries on this list. One for real
Fdinfo associated with master peer and one for
our new generated Fdfinfo entry, it depends on
pid which one become a file master.

Finally we do use post_open_fd hook in our
tty code which allows us to open controlling
terminal and yield proper ioctl on it.

v2:
 - restore control terminals via service fd,
   still need to speedup service fd retrieval.

v3:
 - use prepare_ctl_tty() helper to generate
   control terminal fdinfo entry

v4:
 - use post_open_fd

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
zdtm: Add pty01 test

Two slaves on same pty.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
zdtm: Add pty02 test

The test is tricky -- it opens master in task 1
and dup it in task 2, then close in task 1 and
do C/R.

Thus we need to setup SID of master terminal
somehow in children, which usually fails in
currnt tty restore implementation.

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
zdtm: Add pty03 test

Non-opened control terminal

* Set a control terminal
* Close a file descriptor on it
* Dump/restore
* Open the control terminal (/dev/tty)
* Check, that it connected to the master end

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
zdtm: Add pty04 test

Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
app-test: check screen application

Add test for screen c/r.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>