[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 <lduncan@suse.com>
Acked-by: Kai Makisara <kai.makisara@kolumbus.fi>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>

diff --git a/Documentation/scsi/st.txt b/Documentation/scsi/st.txt
index 691ca29..685bf35 100644 (file)
--- a/Documentation/scsi/st.txt
+++ b/Documentation/scsi/st.txt
@@ -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

diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 9262cdf..8c663e1 100644 (file)
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -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);

diff --git a/drivers/scsi/st.h b/drivers/scsi/st.h
index f91a67c..ea35632 100644 (file)
--- a/drivers/scsi/st.h
+++ b/drivers/scsi/st.h
@@ -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 */
 

diff --git a/include/linux/mtio.h b/include/linux/mtio.h
index 8f82575..18543e2 100644 (file)
--- a/include/linux/mtio.h
+++ b/include/linux/mtio.h
@@ -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