target/file: Use O_DSYNC by default for FILEIO backends

commit a4dff3043c231d57f982af635c9d2192ee40e5ae upstream.

Convert to use O_DSYNC for all cases at FILEIO backend creation time to
avoid the extra syncing of pure timestamp updates with legacy O_SYNC during
default operation as recommended by hch.  Continue to do this independently of
Write Cache Enable (WCE) bit, as WCE=0 is currently the default for all backend
devices and enabled by user on per device basis via attrib/emulate_write_cache.

This patch drops the now unnecessary fd_buffered_io= token usage that was
originally signalling when to explictly disable O_SYNC at backend creation
time for buffered I/O operation.  This can end up being dangerous for a number
of reasons during physical node failure, so go ahead and drop this option
for now when O_DSYNC is used as the default.

Also allow explict FUA WRITEs -> vfs_fsync_range() call to function in
fd_execute_cmd() independently of WCE bit setting.

Reported-by: Christoph Hellwig <hch@lst.de>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
[bwh: Backported to 3.2:
 - We have fd_do_task() and not fd_execute_cmd()
 - Various fields are in struct se_task rather than struct se_cmd
 - fd_create_virtdevice() flags initialisation hasn't been cleaned up]

1 files changed, 0 insertions, 1 deletions

diff --git a/drivers/target/target_core_file.h b/drivers/target/target_core_file.h
index 59e6e73..53ece69 100644
--- a/drivers/target/target_core_file.h
+++ b/drivers/target/target_core_file.h
@@ -18,7 +18,6 @@ struct fd_request {
 
 #define FBDF_HAS_PATH		0x01
 #define FBDF_HAS_SIZE		0x02
-#define FDBD_USE_BUFFERED_IO	0x04
 
 struct fd_dev {
 	u32		fbd_flags;