syscall: add sys_mremap

It will be used in restorer.c

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
bitmap: add a function for finding the next set bit in a memory region

This code is borrowed from the Linux kernel sources.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
mm: add a macros to determing private vma-s (v2)

Now this macros returns true only for anon | priv vmas.
It will be expanded to file | priv in a follow patch.

v2: check flags together.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: split read_and_open_vmas into parts read_vmas and open_vmas (v2)

read_vmas will be called bedore forking children to restore
copy-on-write memory.

v2: don't open an image one more time

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: don't add unneeded vma with zero start and end addresses

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: don't worry if an vma image file is absent

read_vmas will be called for zombies

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: release all previous entries from the vma list

Those will be inherited from parent. Before this patch this list was
always empty, but it will change soon.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: Make target vmas list global

Makes further patching simpler

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: collect vma-s before creating children (v3)

A private vma's should be inherited by children for
restoring copy-on-write regions.

v2: free parent's vma-s in this patch.
v3: split patch on two parts

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: add helper for getting a temporary address of vma

A private vma will be mapped in a temporary place and an address will
be saved in vma->shmid, because nobody was used this field for private
vma-s before. For easy reading vma_premmapped_addr will be used for
getting the temporary address.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: map private vma-s before forking children (v3)

In this case private vma-s will be inherited by children,
it allows to restore copy-on-write reqions.

This code compares child and parent vma lists. If it found
two vma-s with the same start and end addresses, it decides
that the child inherites this vmas from the parent.

This code calculates a size of all private vma-s, then allocate
a memory region for all vma-s and maps them one by one. If a vma is
inherited it will be remaped to an allocated place.

As a result all vma-s will be placed in a continious memory region
and sorted by start addresses. This logic will be used for remap
vma-s to correct address.

v2: fix accoding with Pavel's comments ( clean up and simplify )
v3: simplify code and check that VMA-s are sorted

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: don't unmap premmapped private vma-s (v2)

Private vma-s are mapped before forking children, then they are
remapped to corrected places in restorer.c.

In restorer all unneeded vma-s are unmaped. VMA-s from premmapped
regions should not be unmaped.

v2: replace guard pages on arithmetic in restorer

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restorer: remap private vmas to correct places (v3)

All private vmas are placed in a premmapped region and
they are sorted by start addresses, so they should be shifted apart.

Here is one more problem with overlapped temporary and target regions,
mremap could not remap such cases directly, so for such cases a vma is
remapped away and then remapped on a target place.

v2: fix accoding with Pavel's comments
v3: add a huge comment with pictures

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: use a new scheme for restoring of file private mappings

With this patch vma->shmid contains file id before mapping a region,
then it contains of a temporary address.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: restore content of private mappings before forking children

It's required for restoring copy-on-write regions.

The similar code will be removed from restorer.c.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restorer: don't need to restore pages content in restorer

All memory content are restored before entering in restorer.c.

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
cr-restore: remove unshared pages from inherited private mappings (v2)

A parent process can change a few pages after forking a child and
all this pages should not be avaliable from the child.

Each vma has a bitmap of existent pages. Parent's and child's bitmaps
can be compared and all pages which are not present in a child bitmap
are dropped.

v2: don't check page_bitmap on NULL

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
restore: add statistics about restored pages

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
zdtm: add new test case for testing logic about COW memory (v2)

This test tests the following combinations:

1. parent and child have a cow-ed mapping
2. parent and child have just coinciding mappings

the pages state in both should be in all possible combinations of

 a. write mapped
 b. read mapped
 c. not touched
 d. before fork
 e. after fork

v2: * wait until a child are not prepared
    * check a FILE | PRIVATE mappings

Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>
tty: Make sure the controlling terminal is restored by session leader

The controling terminal should be sestored by a session leader,
thus we need to test if the SID we've found in process tree
is a leader.

Otherwise we might have pretty interesting situation: the user
passed -j on dump, ie telling us to inherit shell jobs and on
restore procedure the SID get inherited from the crtools but
session leader for this sid doesn't belong to our peocess tree
and thus we should not try to restore controlling terminal
but inherit it as well.

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