From 2ec3182f9c20a9eef0dacc0512cf2ca2df7be5ad Mon Sep 17 00:00:00 2001 From: Dongsu Park Date: Fri, 19 Dec 2014 14:53:03 +0100 Subject: [PATCH] Documentation: update notes in biovecs about arbitrarily sized bios Update block/biovecs.txt so that it includes a note on what kind of effects arbitrarily sized bios would bring to the block layer. Also fix a trivial typo, bio_iter_iovec. Cc: Christoph Hellwig Cc: Kent Overstreet Cc: Jonathan Corbet Cc: linux-doc@vger.kernel.org Signed-off-by: Dongsu Park Signed-off-by: Ming Lin Signed-off-by: Jens Axboe --- Documentation/block/biovecs.txt | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/Documentation/block/biovecs.txt b/Documentation/block/biovecs.txt index 74a32ad52f5300..25689584e6e045 100644 --- a/Documentation/block/biovecs.txt +++ b/Documentation/block/biovecs.txt @@ -24,7 +24,7 @@ particular, presenting the illusion of partially completed biovecs so that normal code doesn't have to deal with bi_bvec_done. * Driver code should no longer refer to biovecs directly; we now have - bio_iovec() and bio_iovec_iter() macros that return literal struct biovecs, + bio_iovec() and bio_iter_iovec() macros that return literal struct biovecs, constructed from the raw biovecs but taking into account bi_bvec_done and bi_size. @@ -109,3 +109,11 @@ Other implications: over all the biovecs in the new bio - which is silly as it's not needed. So, don't use bi_vcnt anymore. + + * The current interface allows the block layer to split bios as needed, so we + could eliminate a lot of complexity particularly in stacked drivers. Code + that creates bios can then create whatever size bios are convenient, and + more importantly stacked drivers don't have to deal with both their own bio + size limitations and the limitations of the underlying devices. Thus + there's no need to define ->merge_bvec_fn() callbacks for individual block + drivers.