[CRIU] link_remap_ok

[Pavel Emelyanov]

On 02/27/2015 12:58 AM, beproject criu wrote:
> __properties_ is present at this path
> /sdcard # lxc-attach -n L -- ls /usr/local/lib/lxc/rootfs/root/dev/__properties__ -l
> -r--r--r--    1 0        0           131072 Feb 26 18:07 /usr/local/lib/lxc/rootfs/root/dev/__properties__
> /sdcard #

If the file exists then link remap shouldn't be created. This is the code that
is involved in this decision:

In check_path_remap():

      ret = fstatat(mntns_root, rpath, &pst, 0);

This is where your path is being fstat-ed and:

      if (ret < 0) {
                /*
                 * Linked file, but path is not accessible (unless any
                 * other error occurred). We can create a temporary link to it
                 * uning linkat with AT_EMPTY_PATH flag and remap it to this
                 * name.
                 */

                if (errno == ENOENT)
                        return dump_linked_remap(rpath + 1, plen - 1,
                                                        ost, lfd, id, nsid);

link remap decision is taken. If you file exists then fstatat() should have
failed. Can you put more debug in this place checking what path is stat-ed 
and finding out where the mntns_root() fd points?

Thanks,
Pavel



> 
> 
> On Fri, Feb 27, 2015 at 3:14 AM, Pavel Emelyanov <xemul at parallels.com <mailto:xemul at parallels.com>> wrote:
> 
>     On 02/27/2015 12:33 AM, beproject criu wrote:
>     > This is the error when is used --link-remap option:
>     > Error (files-reg.c:508): Can't link remap to /usr/local/lib/lxc/rootfs/root/dev/__properties__: No such file or directory
> 
>     Hm... The error ENOENT appears either because either a) criu is run not from user or
>     inside user namespace or b) the dirname of the path in question doesn't exits.
> 
>     Can you find out which of the above is your case?
> 
>     > Also i have another error
>     > Error (mount.c:624): 53:./dev/console doesn't have a proper root mount
> 
>     This is because /dev/console is bind-mounted from outside. Should be fixed by the
>     --ext-mount-map option.
> 
>     > Thanks.
>     >
>     > On Fri, Feb 27, 2015 at 1:10 AM, Pavel Emelyanov <xemul at parallels.com <mailto:xemul at parallels.com> <mailto:xemul at parallels.com <mailto:xemul at parallels.com>>> wrote:
>     >
>     >     On 02/26/2015 10:31 PM, beproject criu wrote:
>     >     > Hi,
>     >     > What is the significance of "link_remap_ok" in cr_options
>     >
>     >     This allows CRIU to modify your filesystem with temporary links
>     >     needed to restore files.
>     >
>     >     http://criu.org/Invisible_files
>     >
>     >     > I am getting following error wihile dumping fd.What could be the reason
>     >     >
>     >     > (02.230588) Error (files-reg.c:472): Can't create link remap for /usr/local/lib/lxc/rootfs/root/dev/__properties__. Use link-remap option.
>     >
>     >     Use the link-remap option ;)
>     >
>     >     # ./criu --help | fgrep link-remap
>     >       --link-remap          allow to link unlinked files back when possible
>     >
>     >     Thanks,
>     >     Pavel
>     >
>     >
>     >
> 
>