[CRIU] [PATCH v5 5/5] mount: Restore binfmt_misc content in case of missing mount

[Pavel Emelyanov]

>>>>> @@ -3355,6 +3365,13 @@ static int populate_mnt_ns(void)
>>>>>  	if (!pms)
>>>>>  		return -1;
>>>>>  
>>>>> +	if (!opts.has_binfmt_misc && stat_image(CR_FD_BINFMT_MISC, &st, 0) == 0) {
>>>>
>>>> This should be the other way. In cr-restore.c we have an array of so called cinfos -- these
>>>> are images that should be pre-loaded during restore. So it's better to add new-style binfmt
>>>> cinfo and read_mnt_ns_img should check cinfo->flags for COLLECT_HAPPENED (not 100% sure it
>>>> handles empty images correctly, plz, check) and add cr-time mount if it had.
>>>
>>> You had suggested to dump any binfmt_misc content (belonging to a mount point or not)
>>> to the file of the same name. So, the new suggestion doesn't work.
>>
>> Why?
> 
> Because in case of binfmt_misc image belongs to a real mount, we should not add a cr-time mount;
> it will be restored when real mount is restored.
> 
> 
> The second thing I should pointed in previous letter, you have suggested to use opts to check
> if image present: https://patchwork.criu.org/patch/1069/:
> 
> "For aufs we have opts.aufs bit. For ... overlayfs (?) we have similar.
> We can add binfmt_misc to opts, or have separate entity to ask "whether fs X was
> mounted" for."
> 
> Why now we are moving to another "check cinfo->flags for COLLECT_HAPPENED" mechanism???

My point was that you don't need to call stat_image() in the place you do
explicitly. Instead, add binfmt cinfo that will try to collect the "new style"
binfmt image and will set the boolean flag about whether or not to add fake
mount.

-- Pavel