Re: [PATCH 00/67] fscache: Rewrite index API and management system

[David Howells]

Steve French <smfrench@xxxxxxxxx> wrote:

> On Thu, Oct 21, 2021 at 5:21 PM Omar Sandoval <osandov@xxxxxxxxxxx> wrote:
> >
> > On Mon, Oct 18, 2021 at 03:50:15PM +0100, David Howells wrote:
> > 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.
> 
> Have changes been made to O_TMPFILE?  It is problematic for network
> filesystems because it is not an atomic operation, and would be great if it
> were possible to create a tmpfile and open it atomically (at the file system
> level).

In this case, it's nothing to do with the network filesystem that's using the
cache per se.  Cachefiles is using tmpfiles on the backing filesystem, so as
long as that's, say, ext4, xfs or btrfs, it should work fine.  The backing
filesystem also needs to support SEEK_HOLE and SEEK_DATA.

I'm not sure I'd recommend putting your cache on a network filesystem.

David