Re: [PATCH next] shmem: minor fixes to splice-read implementation

[Hugh Dickins <hughd@google.com>]

On Mon, 17 Apr 2023, Jens Axboe wrote:
> On Sun, 16 Apr 2023 21:46:16 -0700, Hugh Dickins wrote:
> > generic_file_splice_read() makes a couple of preliminary checks (for
> > s_maxbytes and zero len), but shmem_file_splice_read() is called without
> > those: so check them inside it.  (But shmem does not support O_DIRECT,
> > so no need for that one here - and even if O_DIRECT support were stubbed
> > in, it would still just be using the page cache.)
> > 
> > HWPoison: my reading of folio_test_hwpoison() is that it only tests the
> > head page of a large folio, whereas splice_folio_into_pipe() will splice
> > as much of the folio as it can: so for safety we should also check the
> > has_hwpoisoned flag, set if any of the folio's pages are hwpoisoned.
> > (Perhaps that ugliness can be improved at the mm end later.)
> > 
> > [...]
> 
> Applied, thanks!
> 
> [1/1] shmem: minor fixes to splice-read implementation
>       commit: 72887c976a7c9ee7527f4a2e3d109576efea98ab
> 
> Best regards,
> -- 
> Jens Axboe

Thanks, but it then vanished amidst the subsequent splice convulsions,
and I can't quite tell how much of it is still needed - looks like the
!len check is now done in vfs_splice_read(), but I didn't work out
what happened to ppos and s_maxbytes; the hwpoison and "part" mods
still needed, surely?

Hugh