linux-kernel - [PATCH 10/10] Documentation: update notes in biovecs about arbitrarily sized bios

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Message-Id: <1430203717-13307-11-git-send-email-mlin@kernel.org>
Date:	Mon, 27 Apr 2015 23:48:37 -0700
From:	Ming Lin <mlin@...nel.org>
To:	linux-kernel@...r.kernel.org
Cc:	Christoph Hellwig <hch@....de>, Jens Axboe <axboe@...nel.dk>,
	Kent Overstreet <kent.overstreet@...il.com>,
	Dongsu Park <dongsu.park@...fitbricks.com>,
	Ming Lin <mlin@...nel.org>,
	Christoph Hellwig <hch@...radead.org>,
	Jonathan Corbet <corbet@....net>, linux-doc@...r.kernel.org
Subject: [PATCH 10/10] Documentation: update notes in biovecs about arbitrarily sized bios

From: Dongsu Park <dongsu.park@...fitbricks.com>

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 <hch@...radead.org>
Cc: Kent Overstreet <kent.overstreet@...il.com>
Cc: Jonathan Corbet <corbet@....net>
Cc: linux-doc@...r.kernel.org
Signed-off-by: Dongsu Park <dongsu.park@...fitbricks.com>
Signed-off-by: Ming Lin <mlin@...nel.org>
---
 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 74a32ad..2568958 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.
-- 
1.9.1

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