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SCSI st: expand ability to write immediate filemarks

PATCH In review Lee Duncan 2 participants 2 messages Mar 1, 2012 – Mar 4, 2012

Subsystems (3)
Documentation SCSI SCSI tape driver
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Lee Duncan

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PATCH 1/1 SCSI st: expand ability to write immediate filemarks

The st tape driver recently added the MTWEOFI ioctl, which writes a tape filemark (EOF), like the MTWEOF ioctl, except that MTWEOFI returns immediately. This makes certain applications, like backup software, run much more quickly on buffered tape drives.

Since legacy applications do not know about this new MTWEOFI ioctl, this patch adds a new ioctl option that tells the st driver to return immediately when writing an EOF (i.e. a filemark). This new flag is much like the existing flag that tells the st driver to perform writes (and certain other IOs) immediately, but this new flag only applies to writing EOFs.

This new feature is controlled via the MTSETDRVBUFFER ioctl, using the newly-defined MT_ST_NOWAIT_EOF flag.

Use of this new feature is displayed via the sysfs tape "options" attribute.

The st documentation was updated to mention this new flag, as well as the problems that can occur from using it.

Signed-off-by Lee Duncan <[email protected]>
---
 Documentation/scsi/st.txt |    4 ++++
 drivers/scsi/st.c         |   21 ++++++++++++++++++---
 drivers/scsi/st.h         |    1 +
 include/linux/mtio.h      |    1 +
 4 files changed, 24 insertions(+), 3 deletions(-)
Documentation/scsi/st.txt +4 -0
index 691ca29..14b6e5a 100644
@@ -390,6 +390,10 @@ MTSETDRVBUFFER
 	     MT_ST_SYSV sets the SYSV semantics (mode)
 	     MT_ST_NOWAIT enables immediate mode (i.e., don't wait for
 	        the command to finish) for some commands (e.g., rewind)
+	     MT_ST_NOWAIT_EOF enables immediate filemark mode (i.e. when
+	        writing a filemark, don't wait for it to complete). Please
+		see the BASICS note about MTWEOFI with respect to the
+		possible dangers of writing immediate filemarks.
 	     MT_ST_SILI enables setting the SILI bit in SCSI commands when
 		reading in variable block mode to enhance performance when
 		reading blocks shorter than the byte count; set this only
drivers/scsi/st.c +18 -3
index 9262cdf..8c663e1 100644
@@ -1106,6 +1106,12 @@ static int check_tape(struct scsi_tape *STp, struct file *filp)
                                     STp->drv_buffer));
 		}
 		STp->drv_write_prot = ((STp->buffer)->b_data[2] & 0x80) != 0;
+		if (!STp->drv_buffer && STp->immediate_filemark) {
+			printk(KERN_WARNING
+			    "%s: non-buffered tape: disabling writing immediate filemarks\n",
+			    name);
+			STp->immediate_filemark = 0;
+		}
 	}
 	st_release_request(SRpnt);
 	SRpnt = NULL;

@@ -1314,6 +1320,8 @@ static int st_flush(struct file *filp, fl_owner_t id)
 
 		memset(cmd, 0, MAX_COMMAND_SIZE);
 		cmd[0] = WRITE_FILEMARKS;
+		if (STp->immediate_filemark)
+			cmd[1] = 1;
 		cmd[4] = 1 + STp->two_fm;
 
 		SRpnt = st_do_scsi(NULL, STp, cmd, 0, DMA_NONE,

@@ -2181,8 +2189,9 @@ static void st_log_options(struct scsi_tape * STp, struct st_modedef * STm, char
 		       name, STm->defaults_for_writes, STp->omit_blklims, STp->can_partitions,
 		       STp->scsi2_logical);
 		printk(KERN_INFO
-		       "%s:    sysv: %d nowait: %d sili: %d\n", name, STm->sysv, STp->immediate,
-			STp->sili);
+		       "%s:    sysv: %d nowait: %d sili: %d nowait_filemark: %d\n",
+		       name, STm->sysv, STp->immediate, STp->sili,
+		       STp->immediate_filemark);
 		printk(KERN_INFO "%s:    debugging: %d\n",
 		       name, debugging);
 	}

@@ -2224,6 +2233,7 @@ static int st_set_options(struct scsi_tape *STp, long options)
 			STp->can_partitions = (options & MT_ST_CAN_PARTITIONS) != 0;
 		STp->scsi2_logical = (options & MT_ST_SCSI2LOGICAL) != 0;
 		STp->immediate = (options & MT_ST_NOWAIT) != 0;
+		STp->immediate_filemark = (options & MT_ST_NOWAIT_EOF) != 0;
 		STm->sysv = (options & MT_ST_SYSV) != 0;
 		STp->sili = (options & MT_ST_SILI) != 0;
 		DEB( debugging = (options & MT_ST_DEBUGGING) != 0;

@@ -2255,6 +2265,8 @@ static int st_set_options(struct scsi_tape *STp, long options)
 			STp->scsi2_logical = value;
 		if ((options & MT_ST_NOWAIT) != 0)
 			STp->immediate = value;
+		if ((options & MT_ST_NOWAIT_EOF) != 0)
+			STp->immediate_filemark = value;
 		if ((options & MT_ST_SYSV) != 0)
 			STm->sysv = value;
 		if ((options & MT_ST_SILI) != 0)

@@ -2714,7 +2726,8 @@ static int st_int_ioctl(struct scsi_tape *STp, unsigned int cmd_in, unsigned lon
 		cmd[0] = WRITE_FILEMARKS;
 		if (cmd_in == MTWSM)
 			cmd[1] = 2;
-		if (cmd_in == MTWEOFI)
+		if (cmd_in == MTWEOFI ||
+		    (cmd_in == MTWEOF && STp->immediate_filemark))
 			cmd[1] |= 1;
 		cmd[2] = (arg >> 16);
 		cmd[3] = (arg >> 8);

@@ -4093,6 +4106,7 @@ static int st_probe(struct device *dev)
 	tpnt->scsi2_logical = ST_SCSI2LOGICAL;
 	tpnt->sili = ST_SILI;
 	tpnt->immediate = ST_NOWAIT;
+	tpnt->immediate_filemark = 0;
 	tpnt->default_drvbuffer = 0xff;		/* No forced buffering */
 	tpnt->partition = 0;
 	tpnt->new_partition = 0;

@@ -4478,6 +4492,7 @@ st_options_show(struct device *dev, struct device_attribute *attr, char *buf)
 	options |= STp->scsi2_logical ? MT_ST_SCSI2LOGICAL : 0;
 	options |= STm->sysv ? MT_ST_SYSV : 0;
 	options |= STp->immediate ? MT_ST_NOWAIT : 0;
+	options |= STp->immediate_filemark ? MT_ST_NOWAIT_EOF : 0;
 	options |= STp->sili ? MT_ST_SILI : 0;
 
 	l = snprintf(buf, PAGE_SIZE, "0x%08x\n", options);
drivers/scsi/st.h +1 -0
index f91a67c..ea35632 100644
@@ -120,6 +120,7 @@ struct scsi_tape {
 	unsigned char c_algo;			/* compression algorithm */
 	unsigned char pos_unknown;			/* after reset position unknown */
 	unsigned char sili;			/* use SILI when reading in variable b mode */
+	unsigned char immediate_filemark;	/* write filemark immediately */
 	int tape_type;
 	int long_timeout;	/* timeout for commands known to take long time */
include/linux/mtio.h +1 -0
index 8f82575..18543e2 100644
@@ -194,6 +194,7 @@ struct	mtpos {
 #define MT_ST_SYSV              0x1000
 #define MT_ST_NOWAIT            0x2000
 #define MT_ST_SILI		0x4000
+#define MT_ST_NOWAIT_EOF	0x8000
 
 /* The mode parameters to be controlled. Parameter chosen with bits 20-28 */
 #define MT_ST_CLEAR_DEFAULT	0xfffff
Signature · 1 line
1.7.8.3
Acked-by on v1 1/1
#1 lore raw
Quoted 15 lines · Lee Duncan

The st tape driver recently added the MTWEOFI ioctl, which writes a tape filemark (EOF), like the MTWEOF ioctl, except that MTWEOFI returns immediately. This makes certain applications, like backup software, run much more quickly on buffered tape drives.

Since legacy applications do not know about this new MTWEOFI ioctl, this patch adds a new ioctl option that tells the st driver to return immediately when writing an EOF (i.e. a filemark). This new flag is much like the existing flag that tells the st driver to perform writes (and certain other IOs) immediately, but this new flag only applies to writing EOFs.

This new feature is controlled via the MTSETDRVBUFFER ioctl, using the newly-defined MT_ST_NOWAIT_EOF flag.

Quoted 7 lines

Use of this new feature is displayed via the sysfs tape "options" attribute.

The st documentation was updated to mention this new flag, as well as the problems that can occur from using it.

Signed-off-by Lee Duncan <[email protected]>
Acked-by Kai Makisara <[email protected]>
Quoted 6 lines
---
 Documentation/scsi/st.txt |    4 ++++
 drivers/scsi/st.c         |   21 ++++++++++++++++++---
 drivers/scsi/st.h         |    1 +
 include/linux/mtio.h      |    1 +
 4 files changed, 24 insertions(+), 3 deletions(-)

Thanks,
Kai