[CRIU] [PATCH 0/4] restore: handle a case when some mounts are overmounted

[Andrey Vagin]

On Fri, May 13, 2016 at 6:36 AM, Pavel Emelyanov <xemul at virtuozzo.com> wrote:
> On 05/13/2016 01:34 AM, Andrey Vagin wrote:
>> From: Andrew Vagin <avagin at virtuozzo.com>
>>
>> Here are two hacks how to handle this problem:
>> 1. If a whole mount is overmounted, we use a file descriptor to access it
>> 2. If only a part is overmountecd, we create a copyt of this mount without children.
>
> Question -- why not use file descriptor always?

It can't handle a second case or you will need to open a file
descriptor for each bind-mount, because each of them can bind-mount
different parts of a file system.

mi->bind (source mount) can be set a few times and you will need to
open a new descriptor each time. It occurs when we mount a first mount
in a shared group. In this case we change mi->bind for all members
from this group.

>
>> Andrei Vagin (1):
>>   mount: create a clean mount only when it's required
>>   [v4] mount: open a mount point if it's going to be overmounted
>>   mount: return a relative path from cut_root_for_bind()
>>   zdtm: add a test to check a case when two mounts in the same directory
>>
>>  criu/include/mount.h                  |  1 +
>>  criu/mount.c                          | 55 ++++++++++++++++++++++++---
>>  test/zdtm/.gitignore                  |  1 +
>>  test/zdtm/static/Makefile             |  1 +
>>  test/zdtm/static/mntns_overmount.c    | 70 +++++++++++++++++++++++++++++++++++
>>  test/zdtm/static/mntns_overmount.desc |  1 +
>>  6 files changed, 123 insertions(+), 6 deletions(-)
>>  create mode 100644 test/zdtm/static/mntns_overmount.c
>>  create mode 100644 test/zdtm/static/mntns_overmount.desc
>>
>