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Date: Thu, 31 May 2012 01:25:02 -0700
From: "Nicholas A. Bellinger" <nab@...ux-iscsi.org>
To: Christoph Hellwig <hch@....de>
Cc: target-devel <target-devel@...r.kernel.org>,
linux-scsi <linux-scsi@...r.kernel.org>,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
linux-kernel <linux-kernel@...r.kernel.org>,
Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH] target/file: Drop O_SYNC in favor of implict
vfs_fsync_range for writes
On Thu, 2012-05-31 at 07:42 +0200, Christoph Hellwig wrote:
> On Wed, May 30, 2012 at 11:57:43PM +0000, Nicholas A. Bellinger wrote:
> > From: Nicholas Bellinger <nab@...ux-iscsi.org>
> >
> > This patch converts fd_execute_cmd() code to drop O_SYNC usage
> > (the original default) in favor of always preforming an implict
> > SCSI forced unit access (FUA) operation using vfs_fsync_range()
> > based on LBA + SectorCount after each completed FILEIO backend write.
> >
> > This conversion was inspired by Linus's thoughts on O_SYNC usage in
> > the thread: http://www.spinics.net/lists/linux-fsdevel/msg55681.html
> >
> > "O_SYNC is the absolutely anti-thesis of that kind of "multiple levels
> > of overlapping IO". Because it requires that the IO is _done_ by the
> > time you start more, which is against the whole point."
> >
> > This patch also drops the now unnecessary fd_buffered_io= token usage
> > at createvirtdev time. Tested with lio-core code using fio writeverify
> > to local tcm_loop + FILEIO <-> scsi_debug backed LUNs.
>
> If you look at the implementation O_SYNC really just means an implicit
> vfs_fsync_range after each write, thus I can't see how this patch makes any
> difference.
>
But O_SYNC still means more than just vfs_fsync_range() for writes in
other cases, yes..? ;)
>
>
> For target use with WCE=0 semantics you could at least switch to O_DSYNC, though.
Since we currently need to know the flags for flip_open() at
fd_create_virtdevice() setup time with WCE=0 as the default for all
backends, the emulate_write_cache device attribute function to signal
this to SCSI Initiator LUNs is (already) acting independently of O_SYNC
flag usage.
Based on your comments off-list, here is a v2 to always use O_DSYNC by
default, and continue to allow WCE bit to function independently of
flip_open() flags..
WDYT..?
--nab
[PATCH-v2] target/file: Use O_DSYNC by default for FILEIO backends
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 signaling when to explicitly 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@....de>
Cc: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Nicholas Bellinger <nab@...ux-iscsi.org>
---
drivers/target/target_core_file.c | 70 +++++++++----------------------------
drivers/target/target_core_file.h | 1 -
2 files changed, 17 insertions(+), 54 deletions(-)
diff --git a/drivers/target/target_core_file.c b/drivers/target/target_core_file.c
index 686dba1..9f99d04 100644
--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -133,16 +133,11 @@ static struct se_device *fd_create_virtdevice(
ret = PTR_ERR(dev_p);
goto fail;
}
-
- /* O_DIRECT too? */
- flags = O_RDWR | O_CREAT | O_LARGEFILE;
-
/*
- * If fd_buffered_io=1 has not been set explicitly (the default),
- * use O_SYNC to force FILEIO writes to disk.
+ * Use O_DSYNC by default instead of O_SYNC to forgo syncing
+ * of pure timestamp updates.
*/
- if (!(fd_dev->fbd_flags & FDBD_USE_BUFFERED_IO))
- flags |= O_SYNC;
+ flags = O_RDWR | O_CREAT | O_LARGEFILE | O_DSYNC;
file = filp_open(dev_p, flags, 0600);
if (IS_ERR(file)) {
@@ -380,23 +375,6 @@ static void fd_emulate_sync_cache(struct se_cmd *cmd)
}
}
-static void fd_emulate_write_fua(struct se_cmd *cmd)
-{
- struct se_device *dev = cmd->se_dev;
- struct fd_dev *fd_dev = dev->dev_ptr;
- loff_t start = cmd->t_task_lba *
- dev->se_sub_dev->se_dev_attrib.block_size;
- loff_t end = start + cmd->data_length;
- int ret;
-
- pr_debug("FILEIO: FUA WRITE LBA: %llu, bytes: %u\n",
- cmd->t_task_lba, cmd->data_length);
-
- ret = vfs_fsync_range(fd_dev->fd_file, start, end, 1);
- if (ret != 0)
- pr_err("FILEIO: vfs_fsync_range() failed: %d\n", ret);
-}
-
static int fd_execute_cmd(struct se_cmd *cmd, struct scatterlist *sgl,
u32 sgl_nents, enum dma_data_direction data_direction)
{
@@ -411,19 +389,21 @@ static int fd_execute_cmd(struct se_cmd *cmd, struct scatterlist *sgl,
ret = fd_do_readv(cmd, sgl, sgl_nents);
} else {
ret = fd_do_writev(cmd, sgl, sgl_nents);
-
+ /*
+ * Perform implict vfs_fsync_range() for fd_do_writev() ops
+ * for SCSI WRITEs with Forced Unit Access (FUA) set.
+ * Allow this to happen independent of WCE=0 setting.
+ */
if (ret > 0 &&
- dev->se_sub_dev->se_dev_attrib.emulate_write_cache > 0 &&
dev->se_sub_dev->se_dev_attrib.emulate_fua_write > 0 &&
(cmd->se_cmd_flags & SCF_FUA)) {
- /*
- * We might need to be a bit smarter here
- * and return some sense data to let the initiator
- * know the FUA WRITE cache sync failed..?
- */
- fd_emulate_write_fua(cmd);
- }
+ struct fd_dev *fd_dev = dev->dev_ptr;
+ loff_t start = cmd->t_task_lba *
+ dev->se_sub_dev->se_dev_attrib.block_size;
+ loff_t end = start + cmd->data_length;
+ vfs_fsync_range(fd_dev->fd_file, start, end, 1);
+ }
}
if (ret < 0) {
@@ -442,7 +422,6 @@ enum {
static match_table_t tokens = {
{Opt_fd_dev_name, "fd_dev_name=%s"},
{Opt_fd_dev_size, "fd_dev_size=%s"},
- {Opt_fd_buffered_io, "fd_buffered_io=%d"},
{Opt_err, NULL}
};
@@ -454,7 +433,7 @@ static ssize_t fd_set_configfs_dev_params(
struct fd_dev *fd_dev = se_dev->se_dev_su_ptr;
char *orig, *ptr, *arg_p, *opts;
substring_t args[MAX_OPT_ARGS];
- int ret = 0, arg, token;
+ int ret = 0, token;
opts = kstrdup(page, GFP_KERNEL);
if (!opts)
@@ -498,19 +477,6 @@ static ssize_t fd_set_configfs_dev_params(
" bytes\n", fd_dev->fd_dev_size);
fd_dev->fbd_flags |= FBDF_HAS_SIZE;
break;
- case Opt_fd_buffered_io:
- match_int(args, &arg);
- if (arg != 1) {
- pr_err("bogus fd_buffered_io=%d value\n", arg);
- ret = -EINVAL;
- goto out;
- }
-
- pr_debug("FILEIO: Using buffered I/O"
- " operations for struct fd_dev\n");
-
- fd_dev->fbd_flags |= FDBD_USE_BUFFERED_IO;
- break;
default:
break;
}
@@ -542,10 +508,8 @@ static ssize_t fd_show_configfs_dev_params(
ssize_t bl = 0;
bl = sprintf(b + bl, "TCM FILEIO ID: %u", fd_dev->fd_dev_id);
- bl += sprintf(b + bl, " File: %s Size: %llu Mode: %s\n",
- fd_dev->fd_dev_name, fd_dev->fd_dev_size,
- (fd_dev->fbd_flags & FDBD_USE_BUFFERED_IO) ?
- "Buffered" : "Synchronous");
+ bl += sprintf(b + bl, " File: %s Size: %llu Mode: O_DSYNC\n",
+ fd_dev->fd_dev_name, fd_dev->fd_dev_size);
return bl;
}
diff --git a/drivers/target/target_core_file.h b/drivers/target/target_core_file.h
index fbd59ef..70ce7fd 100644
--- a/drivers/target/target_core_file.h
+++ b/drivers/target/target_core_file.h
@@ -14,7 +14,6 @@
#define FBDF_HAS_PATH 0x01
#define FBDF_HAS_SIZE 0x02
-#define FDBD_USE_BUFFERED_IO 0x04
struct fd_dev {
u32 fbd_flags;
--
1.7.2.5
--
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