Re: [RFC/PATCH] block: undeprecate ll_rw_block()

[Jens Axboe <axboe@suse.de>]

On Tue, Feb 07 2006, Pekka J Enberg wrote:
> On Mon, Feb 06 2006, Pekka Enberg wrote:
> > > This patch removes the DEPRECATED comment from ll_rw_block(). The function
> > > is still in active use and there isn't any real replacement for it.
> 
> On Mon, 6 Feb 2006, Jens Axboe wrote:
> > It is still deprecated, so I think the comment should stay. There are
> > plenty ways to accomplish what ll_rw_block does (and more efficiently,
> > array of bh's is not very nice to say the least) and the buffer_head
> > isn't even an io unit anymore.
> 
> To clarify, what ways are there? When we need to access the data, use
> submit_bh() and when we just want the I/O to be done,
> generic_make_request()?

Generally you want to move to using a bio instead of a bh. Once you do
that, you can submit > 1 page of io a lot more efficiently than what
ll_rw_block() is doing. submit_bh() is just a 'wrapper' on top of the
real io interface, your explanation of the two doesn't make sense.

generic_make_request() is typically something a low level driver like md
or dm would use to submit a formed bio to a device, it's not something
you'd expect other parts of the kernel to use. If you look at the newer
io parts in the kernel (in fs/ and mm/), you'll see them using
submit_bio() mostly.

-- 
Jens Axboe

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