[CRIU] [PATCH] stats/pid-reuse: put stats to image directory instead of cwd

[Cyrill Gorcunov]

On Mon, Mar 26, 2018 at 01:43:11PM +0300, Pavel Emelyanov wrote:
> On 03/26/2018 12:16 PM, Pavel Tikhomirov wrote:
> > On 03/26/2018 11:54 AM, Pavel Emelyanov wrote:
> >> On 03/26/2018 11:12 AM, Pavel Tikhomirov wrote:
> >>> Statistics for a special dump/pre-dump/restore action should be
> >>> collected in the images directory of these action. We need these for
> >>> pid-reuse detection as we need to read the stats of parent predump.
> >>
> >> What's wrong with checking pid-reuse form stats sitting in workdir?
> > 
> > We can read previous dump statistics from workdir before 
> > cr_*dump_finish, I agree with that, it is easy.
> > 
> > But Kirill says that "writing image outside of image directory is 
> 
> Stats file is not an image. We just use PB format for it and reuse existing
> image-writing machinery.

Stats file is context dependant and logically bound to images. At least
keeping it inside image drectory gives you confidence the data written
there belongs exactly to the images produced. Because pid reuse uses
data from stats to operate on memory engine it become not longer
a random stat just to view, but mandatory data required for proper
restore.

If you still prefer stats file to be on its own then I think we
need use some other image to carry this information.

> > architectural problem", actually I think these way too for at least two 
> > reasons:
> > 
> > 1) When stats image is in images dir we can latter analize stats for 
> > each iteration if we want it. Now doing migration in VZ7 we have only 
> > stats of last dump in the end.
> 
> The same problem's for log files (I hope nobody has moved them into images dir
> so far), isn't it? Use separate workdir for each iteration.

Exactly, same problem. And for vz7 the logs are kept in the image
directory via vzctl option passed. Thus when a user comes to us with
a problem we ask him to provide us logs from the image directory and
if logs on self are not enough we can ask to pack images directory
where the *complete* state of everything is present which we need
to analyze a problem.