Commit dca69288 authored Nov 11, 2013 by Steve French

[CIFS] O_DIRECT opens should work on directio mounts



Opens on current cifs/smb2/smb3 mounts with O_DIRECT flag fail
even when caching is disabled on the mount.  This was
reported by those running SMB2 benchmarks who need to
be able to pass O_DIRECT on many of their open calls to
reduce caching effects, but would also be needed by other
applications.

When mounting with forcedirectio ("cache=none") cifs and smb2/smb3
do not go through the page cache and thus opens with O_DIRECT flag
should work (when posix extensions are negotiated we even are
able to send the flag to the server). This patch fixes that
in a simple way.

The 9P client has a similar situation (caching is often disabled)
and takes the same approach to O_DIRECT support ie works if caching
disabled, but if client caching enabled it fails with EINVAL.

A followon idea for a future patch as Pavel noted, could
be that files opened with O_DIRECT could cause us to change
inode->i_fop on the fly from

cifs_file_strict_ops

to

cifs_file_direct_ops

which would allow us to support this on non-forcedirectio mounts
(cache=strict and cache=loose) as well.

Reviewed-by: Pavel Shilovsky <piastry@etersoft.ru>
Signed-off-by: Steve French <smfrench@gmail.com>

parent a8582159

fs/cifs/file.c

+22 −0

Original line number	Diff line number	Diff line
		@@ -3663,6 +3663,27 @@ void cifs_oplock_break(struct work_struct *work)
		}
		}

		/*
		* The presence of cifs_direct_io() in the address space ops vector
		* allowes open() O_DIRECT flags which would have failed otherwise.
		*
		* In the non-cached mode (mount with cache=none), we shunt off direct read and write requests
		* so this method should never be called.
		*
		* Direct IO is not yet supported in the cached mode.
		*/
		static ssize_t
		cifs_direct_io(int rw, struct kiocb iocb, const struct iovec iov,
		loff_t pos, unsigned long nr_segs)
		{
		/*
		* FIXME
		* Eventually need to support direct IO for non forcedirectio mounts
		*/
		return -EINVAL;
		}


		const struct address_space_operations cifs_addr_ops = {
		.readpage = cifs_readpage,
		.readpages = cifs_readpages,
		@@ -3672,6 +3693,7 @@ const struct address_space_operations cifs_addr_ops = {
		.write_end = cifs_write_end,
		.set_page_dirty = __set_page_dirty_nobuffers,
		.releasepage = cifs_release_page,
		.direct_IO = cifs_direct_io,
		.invalidatepage = cifs_invalidate_page,
		.launder_page = cifs_launder_page,
		};