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@xxxxxxxxxxxxxxx> > > > > 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@xxxxxx> Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Nicholas Bellinger <nab@xxxxxxxxxxxxxxx> --- 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 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
