Re: [Qemu-devel] [PATCH 04/21] block/commit: utilize job_exit shim

[Kevin Wolf <kwolf@redhat.com>]

Am 15.08.2018 um 22:52 hat John Snow geschrieben:
> On 08/08/2018 12:29 PM, Kevin Wolf wrote:
> > Am 07.08.2018 um 06:33 hat John Snow geschrieben:
> >> Change the manual deferment to commit_complete into the implicit
> >> callback to job_exit.
> >>
> >> Signed-off-by: John Snow <jsnow@redhat.com>
> > 
> > There is one tricky thing in this patch that the commit message could be
> > a bit more explicit about, which is moving job_completed() to a later
> > point.
> > 
> > This is the code that happens between the old call of job_completed()
> > and the new one:
> > 
> >     /* If bdrv_drop_intermediate() didn't already do that, remove the commit
> >      * filter driver from the backing chain. Do this as the final step so that
> >      * the 'consistent read' permission can be granted.  */
> >     if (remove_commit_top_bs) {
> >         bdrv_child_try_set_perm(commit_top_bs->backing, 0, BLK_PERM_ALL,
> >                                 &error_abort);
> >         bdrv_replace_node(commit_top_bs, backing_bs(commit_top_bs),
> >                           &error_abort);
> >     }
> > 
> >     bdrv_unref(commit_top_bs);
> >     bdrv_unref(top);
> > 
> > As the comment states, bdrv_replace_node() requires that the permission
> > restrictions that the commit job made are already lifted. The most
> > important part is done by the explicit block_job_remove_all_bdrv() call
> > right before this hunk. It still leaves bjob->blk around, which could
> > have implications, but luckily we didn't take any permissions for that
> > one:
> > 
> >     s = block_job_create(job_id, &commit_job_driver, NULL, bs, 0, BLK_PERM_ALL,
> >                          speed, JOB_DEFAULT, NULL, NULL, errp);
> > 
> > So I think we got everything out of the way and bdrv_replace_node() can
> > do what it wants to do.
> > 
> > Kevin
> > 
> 
> I suppose it will be up to the author of a job to be aware of any
> permissions they pick up at creation time that might have an effect on
> the cleanup they wish to do during completion time.

I'm really only talking about the commit job, the specific conversion
in this patch and the terse commit message.

Kevin