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Date: Thu, 9 Aug 2012 19:29:04 -0700 From: Muthu Kumar <muthu.lkml@...il.com> To: Tejun Heo <tj@...nel.org> Cc: Mikulas Patocka <mpatocka@...hat.com>, device-mapper development <dm-devel@...hat.com>, linux-bcache@...r.kernel.org, linux-kernel@...r.kernel.org, axboe@...nel.dk, Kent Overstreet <koverstreet@...gle.com>, vgoyal@...hat.com, yehuda@...newdream.net, sage@...dream.net, agk@...hat.com, drbd-dev@...ts.linbit.com Subject: Re: [dm-devel] [PATCH v5 12/12] block: Only clone bio vecs that are in use Tejun, On Thu, Aug 9, 2012 at 12:01 AM, Tejun Heo <tj@...nel.org> wrote: > Hello, > > On Wed, Aug 08, 2012 at 04:47:46PM -0700, Muthu Kumar wrote: >> You are changing the meaning of __bio_clone() here. In old code, the >> number of io_vecs, bi_idx, bi_vcnt are preserved. But in this modified >> code, you are mapping bio_src's bi_iovec[bi_idx] to bio_dests >> bi_iovec[0] and also restricting the number of allocated io_vecs of >> the clone. It may be useful for cases were we would like a identical >> copy of the original bio (may not be in current code base, but this >> implementation is definitely not what one would expect from the name >> "clone"). > > Implementation details changed somewhat but the high-level semantics > didn't change at all. Any driver not messing with bio internals - and > they shouldn't - shouldn't notice the change. The reason for doing this change is because the code in question is messing with bio internals. No in-kernel drivers > seem to be broken by the change. If you ask me, this looks more like > a bug fix to me where the bug is a silly behavior restricting > usefulness of the interface. > >> May be, call this new implementation some thing else (and use it for bcache)? > > This doesn't only change __bio_clone() but all clone interface stacked > on top of it, so, no way. >This ain't windows. ah... when you put it this way, it gets a different perspective :) Anyway, my point is, we shouldn't make it non-obvious ("clone" should be just "clone"). But, we can always add more comments i guess. Regards, Muthu > > 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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