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

[Kevin Wolf]

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 <address@hidden>

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