[CRIU] [PATCH v2 0/5] support restoring ghost files on readonly mounts

[Andrey Vagin]

On Mon, Sep 17, 2018 at 02:47:52PM +0300, Pavel Tikhomirov wrote:
> We have a problem restoring ghost-files on readonly mounts:
> 
> Failed to resume the CT: PRL_ERR_VZCTL_OPERATION_FAILED (Details: (04.800253)      1: Error (criu/files-reg.c:381): Can't create ghost regfile: Read-only file system
> (04.916178) Error (criu/files-reg.c:868): Couldn't unlink remap 17 lib/x86_64-linux-gnu/libm-2.24.so.dpkg-new.cr.22.ghost: Read-only file system
> (04.916190) Error (criu/files-reg.c:868): Couldn't unlink remap 17 lib/x86_64-linux-gnu/libm-2.24.so.dpkg-new.cr.22.ghost: No such file or directory
> (04.945551) Error (criu/cr-restore.c:2340): Restoring FAILED.
> 
> First improve mnt_is_overmounted helper to use it safely after
> mounts remap.
> 
> Second actually fix the problem by making mounts writable (where
> possible) while restoring files.
> 
> Just to note: I thought about two other possible ways of making these
> work: Find a writable bind-mount - but there can be no such a thing, see
> the third (test) patch. Remount the mount writable just before creating
> ghosts and remount it back after it - we operate ghosts in three places
> (create, give it the right name, remove) so these approach brings a lot
> of extra remounts and is hardly a good way.
> 
> While on it add a check for unsupported open files on overmounted mounts
> early on dump, which also implies ghost-files.
> 
> https://jira.sw.ru/browse/PSBM-82991

Pls avoid non-public linkgs in commit messages

> 
> Pavel Tikhomirov (5):
>   mount: save the result of mnt_is_overmounted
>   mount: delay restoring readonly mount flag until all files ready
>   zdtm: ghost on readonly fs
>   files: open files on overmounted mounts are not supported
>   zdtm: test dumping file on overmounted mount fails
> 
>  criu/cr-restore.c                      |   2 +
>  criu/files-reg.c                       |  13 +-
>  criu/include/mount.h                   |   5 +
>  criu/mount.c                           | 146 ++++++++++++++++++--
>  test/zdtm/static/Makefile              |   2 +
>  test/zdtm/static/ghost_on_rofs.c       | 179 +++++++++++++++++++++++++
>  test/zdtm/static/ghost_on_rofs.desc    |   1 +
>  test/zdtm/static/overmounted_file.c    | 109 +++++++++++++++
>  test/zdtm/static/overmounted_file.desc |   1 +
>  9 files changed, 446 insertions(+), 12 deletions(-)
>  create mode 100644 test/zdtm/static/ghost_on_rofs.c
>  create mode 100644 test/zdtm/static/ghost_on_rofs.desc
>  create mode 100644 test/zdtm/static/overmounted_file.c
>  create mode 100644 test/zdtm/static/overmounted_file.desc
> 
> -- 
> 2.17.1
>