Re: [PATCH] REQ-flags to/from BIO-flags bugfix

David Chinner
2007-12-13T05:46:20Z

On Wed, Dec 12, 2007 at 08:54:07AM -0700, Matthew Wilcox wrote:
> On Wed, Dec 12, 2007 at 08:18:14AM -0700, Matthew Wilcox wrote:
> > I don't know whether BIO_RW_BARRIER is __REQ_SOFTBARRIER or
> > __REQ_HARDBARRIER, so I didn't include that in this patch. There also
> > doesn't seem to be a __REQ equivalent to BIO_RW_AHEAD, but we can do
> > the other four bits (and leave gaps for those two).
>
> Hm. BIO_RW_AHEAD seems unused:
>
> willy@honeydew:~/kernel/linux-2.6$ grep -r BIO_RW_AHEAD *
> block/blktrace.c: (((rw) & (1 << BIO_RW_AHEAD)) << (2 - BIO_RW_AHEAD))
> include/linux/bio.h:#define BIO_RW_AHEAD 1
> include/linux/bio.h:#define bio_rw_ahead(bio) ((bio)->bi_rw & (1 << BIO_RW_AHEAD))
> willy@honeydew:~/kernel/linux-2.6$ grep -r bio_rw_ahead *
> block/ll_rw_blk.c: if (bio_rw_ahead(bio) || bio_failfast(bio))
> drivers/md/dm-mpath.c: if ((error == -EWOULDBLOCK) && bio_rw_ahead(bio))
> drivers/md/multipath.c: else if (!bio_rw_ahead(bio)) {
> include/linux/bio.h:#define bio_rw_ahead(bio) ((bio)->bi_rw & (1 << BIO_RW_AHEAD))

That would say to me that READA is not hooked up correctly. i.e:

#define READ 0
#define WRITE 1
#define READA 2 /* read-ahead - don't block if no resources */
#define SWRITE 3 /* for ll_rw_block() - wait for buffer lock */
#define READ_SYNC (READ | (1 << BIO_RW_SYNC))
#define READ_META (READ | (1 << BIO_RW_META))
#define WRITE_SYNC (WRITE | (1 << BIO_RW_SYNC))
#define WRITE_BARRIER ((1 << BIO_RW) | (1 << BIO_RW_BARRIER))

i.e. it should be:

#define READA (1 << BIO_RW_AHEAD)

Right?

FWIW, dm does this:

if (bio_rw(bio) != READA)

Which really should be if (bio_rw_ahead(bio)).....

Cheers,

Dave.
--
Dave Chinner
Principal Engineer
SGI Australian Software Group