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Date: Wed, 8 Aug 2012 17:07:11 -0700 From: Kent Overstreet <koverstreet@...gle.com> To: Tejun Heo <tj@...nel.org> Cc: linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org, dm-devel@...hat.com, axboe@...nel.dk, agk@...hat.com, neilb@...e.de, drbd-dev@...ts.linbit.com, vgoyal@...hat.com, mpatocka@...hat.com, sage@...dream.net, yehuda@...newdream.net Subject: Re: [PATCH v5 03/12] block: Add bio_reset() On Wed, Aug 08, 2012 at 03:11:29PM -0700, Tejun Heo wrote: > Hello, > > On Mon, Aug 06, 2012 at 03:08:32PM -0700, Kent Overstreet wrote: > > Reusing bios is something that's been highly frowned upon in the past, > > but driver code keeps doing it anyways. If it's going to happen anyways, > > we should provide a generic method. > > > > This'll help with getting rid of bi_destructor - drivers/block/pktcdvd.c > > was open coding it, by doing a bio_init() and resetting bi_destructor. > > > > v5: Add a define BIO_RESET_BITS, to be very explicit about what parts of > > bio->bi_flags are saved. > > > > Signed-off-by: Kent Overstreet <koverstreet@...gle.com> > > Change-Id: I4eb2975bd678d3be811d5423d0620b08020be9ff > > Please drop Change-Id. Die gerrit die. Bah, missed that one. > > +void bio_reset(struct bio *bio) > > +{ > > + unsigned long flags = bio->bi_flags & (~0UL << BIO_RESET_BITS); > > How many flags are we talking about? If there aren't too many, I'd > prefer explicit BIO_FLAGS_PRESERVED or whatever. It mostly isn't actual flags that are preserved - the high bits of the flags are used for indicating what slab the bvec was allocated from, and that's the main thing that has to be preserved. So that's why I went with defining the things that are reset instead of the things that are preserved. I would prefer if bitfields were used for at least BIO_POOL_IDX, but the problem is flags is used as an atomic bit vector for BIO_UPTODATE. But flags isn't treated as an atomic bit vector elsewhere - bio_flagged() doesn't use test_bit(), and flags are set/cleared with atomic bit operations in some places but not in others (probably _most_ of them are technically safe, but... ick). > > Thanks. > > -- > tejun -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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