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target/file: Re-enable optional fd_buffered_io=1 operation 

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 a4dff3043c
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>
Cc: <stable@vger.kernel.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>
This commit is contained in:
Nicholas Bellinger 2012-09-29 17:15:37 -07:00
parent f25590f39d
commit b32f4c7ed8
2 changed files with 39 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

41
drivers/target/target_core_file.c
View File

@ -125,6 +125,19 @@ static struct se_device *fd_create_virtdevice(
* 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_virtdevice(
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_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, token;
int ret = 0, arg, token;
opts = kstrdup(page, GFP_KERNEL);
if (!opts)
@ -459,6 +479,19 @@ 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_HAS_BUFFERED_IO_WCE;
break;
default:
break;
}
@ -490,8 +523,10 @@ 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: 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;
}

1
drivers/target/target_core_file.h
View File

@ -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;