Re: [PATCH 2/3] block: Introduce blk_rq_completed()

[James Bottomley <jbottomley@parallels.com>]

On Tue, 2014-05-27 at 12:47 +0200, Paolo Bonzini wrote:
> Il 27/05/2014 12:21, James Bottomley ha scritto:
> > I could also see us one day extending the TMF capability to abort any
> > running command, which would make even an assertion of block timed out
> > or completed invalid.
> 
> Actually the assertion would remain valid, and that's exactly what Bart 
> wants to document with this assertion.

No, it wouldn't: if we abort a running command by definition the command
hadn't timed out and might not be completed.  This is required by TMF
handling because now you have an abort racing with a completion.  Either
the command completes normally because it misses the abort or the abort
gets to it and its returned status is set to TASK_ABORTED.  That's the
only way you can tell if the abort was successful or not.

If you're thinking we would tell block to ignore returning commands
before issuing the abort, we'd never be able to tell if the abort were
successful, so we have to allow the race to collect the status.

James