linux-kernel - Re: [PATCH 1/2] block: Modify blk_rq_map

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Date:	Wed, 13 Sep 2006 11:30:09 +0200
From:	Jens Axboe <axboe@...nel.dk>
To:	Mike Christie <michaelc@...wisc.edu>
Cc:	linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 1/2] block: Modify blk_rq_map_user to support large requests

On Sat, Sep 09 2006, Mike Christie wrote:
> Currently, there is some duplication between bsg, scsi_ioctl.c
> and scsi_lib.c/sg/st in its mapping code. This patch modifies
> the block layer blk_rq_map_user code to support large requests so
> that the scsi and block drivers can use this common code. The
> changes also make it so the callers do not have to account for
> the bio to be unmapped and bounce buffers.
> 
> The next patch then coverts bsg.c, scsi_ioctl.c and cdrom.c
> to use the updated functions. For scsi_ioctl.c and cdrom.c
> the only thing that changes is that they no longer have
> to do the bounce buffer management and pass in the len for
> the unmapping. The bsg change is a little larger since that
> code was duplicating a lot of code that is now common
> in the block layer. The bsg conversions als should fix
> a memory leak caused when unmapping a hdr with iovec_count=0.
> 
> Patch was made over Jens's block tree and the bsg branch

Generally it looks good - two comments:

- I see some advantages to having biohead_orig to avoid keeping track of
  it and passing it around, but there's also good reasons for _not_
  adding more stuff to struct request. Any particular reason you chose
  to do that?

- blk_get_bounced_bio() looks redundant. BIO_BOUNCED should only be set
  on a bounced bio, and ->bi_private should always hold that bounced
  bio.

-- 
Jens Axboe

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