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

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: Ben Hutchings <ben@decadent.org.uk>

diff --git a/drivers/target/target_core_file.c b/drivers/target/target_core_file.c
index 455a251..cafa477 100644 (file)
--- a/drivers/target/target_core_file.c
+++ b/drivers/target/target_core_file.c
@@ -139,6 +139,19 @@ 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(dev_p, flags, 0600);
        if (IS_ERR(file)) {
@@ -206,6 +219,12 @@ 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;
 
@@ -450,6 +469,7 @@ 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}
 };
 
@@ -461,7 +481,7 @@ 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)
@@ -505,6 +525,19 @@ 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;
                }
@@ -536,8 +569,10 @@ 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;
 }
 

diff --git a/drivers/target/target_core_file.h b/drivers/target/target_core_file.h
index 53ece69..6b1b6a9 100644 (file)
--- a/drivers/target/target_core_file.h
+++ b/drivers/target/target_core_file.h
@@ -18,6 +18,7 @@ struct fd_request {
 
 #define FBDF_HAS_PATH          0x01
 #define FBDF_HAS_SIZE          0x02
+#define FDBD_HAS_BUFFERED_IO_WCE 0x04
 
 struct fd_dev {
        u32             fbd_flags;