On Thu, Apr 28, 2022 at 01:03:49PM -0700, Stefan Roesch wrote:
>
>
> On 4/26/22 3:54 PM, Dave Chinner wrote:
> > On Tue, Apr 26, 2022 at 10:43:23AM -0700, Stefan Roesch wrote:
> >> This adds the async buffered write support to the iomap layer of XFS. If
> >> a lock cannot be acquired or additional reads need to be performed, the
> >> request will return -EAGAIN in case this is an async buffered write request.
> >>
> >> Signed-off-by: Stefan Roesch <shr@xxxxxx>
> >> ---
> >> fs/xfs/xfs_iomap.c | 33 +++++++++++++++++++++++++++++++--
> >> 1 file changed, 31 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> >> index e552ce541ec2..80b6c48e88af 100644
> >> --- a/fs/xfs/xfs_iomap.c
> >> +++ b/fs/xfs/xfs_iomap.c
> >> @@ -881,18 +881,28 @@ xfs_buffered_write_iomap_begin(
> >> bool eof = false, cow_eof = false, shared = false;
> >> int allocfork = XFS_DATA_FORK;
> >> int error = 0;
> >> + bool no_wait = (flags & IOMAP_NOWAIT);
> >>
> >> if (xfs_is_shutdown(mp))
> >> return -EIO;
> >>
> >> /* we can't use delayed allocations when using extent size hints */
> >> - if (xfs_get_extsz_hint(ip))
> >> + if (xfs_get_extsz_hint(ip)) {
> >> + if (no_wait)
> >> + return -EAGAIN;
> >> +
> >> return xfs_direct_write_iomap_begin(inode, offset, count,
> >> flags, iomap, srcmap);
> >
> > Why can't we do IOMAP_NOWAIT allocation here?
> > xfs_direct_write_iomap_begin() supports IOMAP_NOWAIT semantics just
> > fine - that's what the direct IO path uses...
>
> I'll make that change in the next version.
> >
> >> + }
> >>
> >> ASSERT(!XFS_IS_REALTIME_INODE(ip));
> >>
> >> - xfs_ilock(ip, XFS_ILOCK_EXCL);
> >> + if (no_wait) {
> >> + if (!xfs_ilock_nowait(ip, XFS_ILOCK_EXCL))
> >> + return -EAGAIN;
> >> + } else {
> >> + xfs_ilock(ip, XFS_ILOCK_EXCL);
> >> + }
> >
> > handled by xfs_ilock_for_iomap().
>
> The helper xfs_ilock_for_iomap cannot be used for this purpose. The function
> xfs_ilock_for_iomap tries to deduce the lock mode. For the function xfs_file_buffered_write()
> the lock mode must be exclusive. However this is not always the case when the
> helper xfs_ilock_for_iomap is used. There are cases where xfs_is_cow_inode(() is not
> true.
That's trivially fixed by having the caller initialise the lock_mode
to what they want, rather than have the function set the initial
type to SHARED....
> I'll add a new helper that will be used here.
... so I don't think a new helper is needed.
--Dave.
--
Dave Chinner
david@xxxxxxxxxxxxx
