On Mon, Oct 18, 2021 at 03:50:15PM +0100, David Howells wrote:

Here's a set of patches that rewrites and simplifies the fscache index API
to remove the complex operation scheduling and object state machine in
favour of something much smaller and simpler.  It is built on top of the
set of patches that removes the old API[1].

The operation scheduling API was intended to handle sequencing of cache
operations, which were all required (where possible) to run asynchronously
in parallel with the operations being done by the network filesystem, while
allowing the cache to be brought online and offline and interrupt service
with invalidation.

However, with the advent of the tmpfile capacity in the VFS, an opportunity
arises to do invalidation much more easily, without having to wait for I/O
that's actually in progress: Cachefiles can simply cut over its file
pointer for the backing object attached to a cookie and abandon the
in-progress I/O, dismissing it upon completion.

Future work there would involve using Omar Sandoval's vfs_link() with
AT_LINK_REPLACE[2] to allow an extant file to be displaced by a new hard
link from a tmpfile as currently I have to unlink the old file first.

I had forgotten about that. It'd be great to finish that someday, but
given the dead-end of the last discussion [1], we might need to hash it
out the next time we can convene in person.

1:https://lore.kernel.org/linux-fsdevel/364531.1579265357@warthog.procyon.org.uk/ (local)