[Devel] [PATCH criu] files: Allow to dump ploopX files opened

[Maxim Patlasov]

On 08/04/2016 06:43 AM, Cyrill Gorcunov wrote:

> On Thu, Aug 04, 2016 at 04:34:57PM +0300, Pavel Emelyanov wrote:
>>>   
>>> +static int check_blkdev(struct fd_parms *p, int lfd)
>>> +{
>>> +	/*
>>> +	 * @ploop_major is module parameter actually,
>>> +	 * set to PLOOP_DEVICE_MAJOR by default. We may
>>> +	 * need to scan module params or access
>>> +	 * /sys/block/ploopX/dev to fetch major.
>>> +	 *
>>> +	 * For a while simply use predefined @major.
>>> +	 */
>>> +	static const int ploop_major = 182;
>> Major numbers are typically macro-defined and sit in some header ;)
> I don't want to spread Vz7 specific code into headers and such.
>
>>> +	int maj = major(p->stat.st_rdev);
>>> +
>>> +	/*
>>> +	 * It's been found that systemd-udevd sometimes
>>> +	 * opens-up ploop device from inside of container,
>>> +	 * so allow him to do that.
>>> +	 */
>>> +	if (maj == ploop_major)
>>> +		return 0;
>> This worries me :( Ploop has some internal state, so if we catch a proggie
>> that configures that state, live migrate it and just re-open the ploop it
>> will __continue__ configuring that state and, since we've re-opened the
>> ploop from the beginning, this configuration will continue with an error...
> Then we need to liftup this code and someone from ploop camp should help me
> to gather ploop props which we could dump into image and restore then.

Assuming that we refuse to checkpoint ploop if its maintenance state != 
OFF, the following:
/sys/block/ploopX/pstate/*
/sys/block/ploopX/pdelta/*/*
may be enough. If it's not, let me know, and we'll think how to fix it.

Btw, please keep all the code interacting with ploop (ioctls, 
/sys/block/ploopX/*) in libploop.

Thanks,
Maxim

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