On Tue, Nov 21, 2023 at 11:30 PM Dave Chinner <david@xxxxxxxxxxxxx> wrote:
>
> On Tue, Nov 21, 2023 at 04:00:32PM -0500, Josef Bacik wrote:
> > On Tue, Nov 21, 2023 at 03:25:51PM +0200, Amir Goldstein wrote:
> > > We want to move kiocb_start_write() into vfs_iocb_iter_write(), after
> > > the permission hook, but leave kiocb_end_write() in the write completion
> > > handler of the callers of vfs_iocb_iter_write().
> > >
> > > After this change, there will be no way of knowing in completion handler,
> > > if write has failed before or after calling kiocb_start_write().
> > >
> > > Add a flag IOCB_WRITE_STARTED, which is set and cleared internally by
> > > kiocb_{start,end}_write(), so that kiocb_end_write() could be called for
> > > cleanup of async write, whether it was successful or whether it failed
> > > before or after calling kiocb_start_write().
> > >
> > > This flag must not be copied by stacked filesystems (e.g. overlayfs)
> > > that clone the iocb to another iocb for io request on a backing file.
> > >
> > > Link: https://lore.kernel.org/r/CAOQ4uxihfJJRxxUhAmOwtD97Lg8PL8RgXw88rH1UfEeP8AtP+w@xxxxxxxxxxxxxx/
> > > Signed-off-by: Amir Goldstein <amir73il@xxxxxxxxx>
> >
> > This is only a problem for cachefiles and overlayfs, and really just for
> > cachefiles because of the error handling thing.
> >
> > What if instead we made vfs_iocb_iter_write() call kiocb_end_write() in the ret
> > != EIOCBQUEUED case, that way it is in charge of the start and the end, and the
> > only case where the file system has to worry about is the actual io completion
> > path when the kiocb is completed.
> >
> > The result is something like what I've pasted below, completely uncompiled and
> > untested. Thanks,
>
> I like this a lot better than an internal flag that allows
> unbalanced start/end calls to proliferate. I find it much easier to
> read the code, determine the correct cleanup is being done and
> maintain the code in future when calls need to be properly
> paired....
Yes! I like it too.
Thank you Josef!
I'll test that and post v2 with your RVBs.
Amir.
