Re: [Kiobuf-io-devel] RFC: Kernel mechanism: Compound event wait /notify + callback chains

Stephen C. Tweedie
2001-02-01T12:21:49Z

Hi,

On Thu, Feb 01, 2001 at 10:25:22AM +0530, bsuparna@in.ibm.com wrote:
>
> >We _do_ need the ability to stack completion events, but as far as the
> >kiobuf work goes, my current thoughts are to do that by stacking
> >lightweight "clone" kiobufs.
>
> Would that work with stackable filesystems ?

Only if the filesystems were using VFS interfaces which used kiobufs.
Right now, the only filesystem using kiobufs is XFS, and it only
passes them down to the block device layer, not to other filesystems.

> Being able to track the children of a kiobuf would help with I/O
> cancellation (e.g. to pull sub-ios off their request queues if I/O
> cancellation for the parent kiobuf was issued). Not essential, I guess, in
> general, but useful in some situations.

What exactly is the justification for IO cancellation? It really
upsets the normal flow of control through the IO stack to have
voluntary cancellation semantics.

--Stephen