Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait

[Stephen C. Tweedie]

Hi,

On Tue, Feb 06, 2001 at 04:41:21PM -0800, Linus Torvalds wrote:
> 
> On Wed, 7 Feb 2001, Stephen C. Tweedie wrote:
> > No, it is a problem of the ll_rw_block interface: buffer_heads need to
> > be aligned on disk at a multiple of their buffer size.
> 
> Ehh.. True of ll_rw_block() and submit_bh(), which are meant for the
> traditional block device setup, where "b_blocknr" is the "virtual
> blocknumber" and that indeed is tied in to the block size.
> 
> The fact is, if you have problems like the above, then you don't
> understand the interfaces. And it sounds like you designed kiobuf support
> around the wrong set of interfaces.

They used the only interfaces available at the time...

> If you want to get at the _sector_ level, then you do
...
> which doesn't look all that complicated to me. What's the problem?

Doesn't this break nastily as soon as the IO hits an LVM or soft raid
device?  I don't think we are safe if we create a larger-sized
buffer_head which spans a raid stripe: the raid mapping is only
applied once per buffer_head.

--Stephen
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