[ 32/76] target/file: Re-enable optional fd_buffered_io=1 operation

Greg Kroah-Hartman
2012-10-19T03:00:15Z

From: Nicholas Bellinger <nab@linux-iscsi.org>

commit b32f4c7ed85c5cee2a21a55c9f59ebc9d57a2463 upstream.

This patch re-adds the ability to optionally run in buffered FILEIO mode
(eg: w/o O_DSYNC) for device backends in order to once again use the
Linux buffered cache as a write-back storage mechanism.

This logic was originally dropped with mainline v3.5-rc commit:

commit a4dff3043c231d57f982af635c9d2192ee40e5ae
Author: Nicholas Bellinger <nab@linux-iscsi.org>
Date: Wed May 30 16:25:41 2012 -0700

target/file: Use O_DSYNC by default for FILEIO backends

This difference with this patch is that fd_create_virtdevice() now
forces the explicit setting of emulate_write_cache=1 when buffered FILEIO
operation has been enabled.

(v2: Switch to FDBD_HAS_BUFFERED_IO_WCE + add more detailed
comment as requested by hch)

Reported-by: Ferry <iscsitmp@bananateam.nl>
Cc: Christoph Hellwig <hch@lst.de>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/target/target_core_file.c | 41 +++++++++++++++++++++++++++++++++++---
drivers/target/target_core_file.h | 1
2 files changed, 39 insertions(+), 3 deletions(-)

--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -125,6 +125,19 @@ static struct se_device *fd_create_virtd
* of pure timestamp updates.
*/
flags = O_RDWR | O_CREAT | O_LARGEFILE | O_DSYNC;
+ /*
+ * Optionally allow fd_buffered_io=1 to be enabled for people
+ * who want use the fs buffer cache as an WriteCache mechanism.
+ *
+ * This means that in event of a hard failure, there is a risk
+ * of silent data-loss if the SCSI client has *not* performed a
+ * forced unit access (FUA) write, or issued SYNCHRONIZE_CACHE
+ * to write-out the entire device cache.
+ */
+ if (fd_dev->fbd_flags & FDBD_HAS_BUFFERED_IO_WCE) {
+ pr_debug("FILEIO: Disabling O_DSYNC, using buffered FILEIO\n");
+ flags &= ~O_DSYNC;
+ }

file = filp_open(fd_dev->fd_dev_name, flags, 0600);
if (IS_ERR(file)) {
@@ -188,6 +201,12 @@ static struct se_device *fd_create_virtd
if (!dev)
goto fail;

+ if (fd_dev->fbd_flags & FDBD_HAS_BUFFERED_IO_WCE) {
+ pr_debug("FILEIO: Forcing setting of emulate_write_cache=1"
+ " with FDBD_HAS_BUFFERED_IO_WCE\n");
+ dev->se_sub_dev->se_dev_attrib.emulate_write_cache = 1;
+ }
+
fd_dev->fd_dev_id = fd_host->fd_host_dev_id_count++;
fd_dev->fd_queue_depth = dev->queue_depth;

@@ -407,6 +426,7 @@ 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}
};

@@ -418,7 +438,7 @@ static ssize_t fd_set_configfs_dev_param
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, token;
+ int ret = 0, arg, token;

opts = kstrdup(page, GFP_KERNEL);
if (!opts)
@@ -459,6 +479,19 @@ static ssize_t fd_set_configfs_dev_param
" 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_HAS_BUFFERED_IO_WCE;
+ break;
default:
break;
}
@@ -490,8 +523,10 @@ static ssize_t fd_show_configfs_dev_para
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: O_DSYNC\n",
- fd_dev->fd_dev_name, fd_dev->fd_dev_size);
+ 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_HAS_BUFFERED_IO_WCE) ?
+ "Buffered-WCE" : "O_DSYNC");
return bl;
}

--- a/drivers/target/target_core_file.h
+++ b/drivers/target/target_core_file.h
@@ -14,6 +14,7 @@

#define FBDF_HAS_PATH 0x01
#define FBDF_HAS_SIZE 0x02
+#define FDBD_HAS_BUFFERED_IO_WCE 0x04

struct fd_dev {
u32 fbd_flags;