Re: Linux Buffer Cache Does Not Support Mirroring

Gerard Roudier (groudier@club-internet.fr)
Wed, 3 Nov 1999 23:30:24 +0100 (MET)


On Wed, 3 Nov 1999, Stephen C. Tweedie wrote:

> If the worst comes to the worst, you can just copy those functions in
> your own module for 2.2 and ask for them to be exported symbols in 2.3.
> The ll_rw_block API just wants something that looks like a buffer_head,
> and doesn't care what code was called to create that structure.

In my opinion, ll_rw_blk is something that may well disappear in 2.5/2.6.
Exporting to much interfaces that refers to this layer may well add some
legacies that will make things still harder for the change.
In my experience, exportation of symbols is something that must be
carefully controlled, otherwise we may end up with some montruous software
that might get pretty impossible to evolve in the future.

About callbacks, they are good when there are not to much abused. They can
cause increase of interrupt latency and kind of wierd problems when not
carefully understood and used. When, for example, we only need a thread
to be waken up, some less general but less permissive mechanism should be
preferred, in my opinion.

Gérard.

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