Re: [PATCH] dm.c - device-mapper I/O path fixes

Denis Vlasenko
2002-12-11T14:36:35Z

On 11 December 2002 12:18, Joe Thornber wrote:
> On Wed, Dec 11, 2002 at 07:16:53AM -0600, Kevin Corry wrote:
> > However, it might be a good idea to consider how bio's keep track
> > of errors. When a bio is created, it is marked UPTODATE. Then, if
> > any part of a bio takes an error, the UPTODATE flag is turned off.
> > When the whole bio completes, if the UPTODATE flag is still on,
> > there were no errors during the i/o. Perhaps the "error" field in
> > "struct dm_io" could be modified to use this method of error
> > tracking? Then we could change dec_pending() to be something like:
> >
> > if (error)
> > clear_bit(DM_IO_UPTODATE, &io->error);
> >
> > with a "set_bit(DM_IO_UPTODATE, &ci.io->error);" in __bio_split().
>
> The problem with this is you don't keep track of the specific error
> to later pass to bio_endio(io->bio...). I guess it all comes down to
> just how expensive that spin lock is; and since locking only occurs
> when there's an error I'm happy with things as they are.

lock();
a = b;
unlock();

Store of ints is atomic anyway. You need locking if a is a larger entity,
say, a struct.
--
vda