| Message ID | 20170405114111.26864-1-martin.petersen@oracle.com (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
On Wed, 2017-04-05 at 07:41 -0400, Martin K. Petersen wrote: > +static const char *zeroing_mode[] = { > + [SD_ZERO_WRITE] = "write", > + [SD_ZERO_WS] = "writesame", > + [SD_ZERO_WS16_UNMAP] = "writesame_16_unmap", > + [SD_ZERO_WS10_UNMAP] = "writesame_10_unmap", > +}; > + > +static ssize_t > +zeroing_mode_show(struct device *dev, struct device_attribute *attr, > + char *buf) > +{ > + struct scsi_disk *sdkp = to_scsi_disk(dev); > + > + return snprintf(buf, 20, "%s\n", zeroing_mode[sdkp->zeroing_mode]); > +} Hello Martin, If anyone would ever add a string to zeroing_mode[] that is longer than 20 characters then zeroing_mode_show() will truncate it. Since all strings in the zeroing_mode[] array are short, have you considered to use sprintf() instead? And if you do not want to use sprintf(), how about using snprintf(buf, PAGE_SIZE, ...)? I'm asking this because I'm no fan of magic constants. > +static ssize_t > +zeroing_mode_store(struct device *dev, struct device_attribute *attr, > + const char *buf, size_t count) > +{ > + struct scsi_disk *sdkp = to_scsi_disk(dev); > + > + if (!capable(CAP_SYS_ADMIN)) > + return -EACCES; > + > + if (!strncmp(buf, zeroing_mode[SD_ZERO_WRITE], 20)) > + sdkp->zeroing_mode = SD_ZERO_WRITE; > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS], 20)) > + sdkp->zeroing_mode = SD_ZERO_WS; > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS16_UNMAP], 20)) > + sdkp->zeroing_mode = SD_ZERO_WS16_UNMAP; > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS10_UNMAP], 20)) > + sdkp->zeroing_mode = SD_ZERO_WS10_UNMAP; > + else > + return -EINVAL; > + > + return count; > +} Since sysfs guarantees that buf is '\0'-terminated, why does the above function call strncmp() instead of strcmp()? Can the above chain of if-statements be replaced by a for-loop such that zeroing_mode_store() won't have to be updated if the zeroing_mode[] array is modified? Thanks, Bart.
On Wed, 2017-04-05 at 07:41 -0400, Martin K. Petersen wrote: > +static ssize_t > +zeroing_mode_store(struct device *dev, struct device_attribute *attr, > + const char *buf, size_t count) > +{ > + struct scsi_disk *sdkp = to_scsi_disk(dev); > + > + if (!capable(CAP_SYS_ADMIN)) > + return -EACCES; > + > + if (!strncmp(buf, zeroing_mode[SD_ZERO_WRITE], 20)) > + sdkp->zeroing_mode = SD_ZERO_WRITE; > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS], 20)) > + sdkp->zeroing_mode = SD_ZERO_WS; > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS16_UNMAP], 20)) > + sdkp->zeroing_mode = SD_ZERO_WS16_UNMAP; > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS10_UNMAP], 20)) > + sdkp->zeroing_mode = SD_ZERO_WS10_UNMAP; > + else > + return -EINVAL; > + > + return count; > +} An additional question about this function: if the shell command "echo" is used without command-line option -n to modify the "zeroing_mode" sysfs attribute then a newline character will be present in buf. Does the above code handle newline characters correctly? Bart.
On Fri, Apr 07, 2017 at 07:59:08PM +0000, Bart Van Assche wrote: > On Wed, 2017-04-05 at 07:41 -0400, Martin K. Petersen wrote: > > +static ssize_t > > +zeroing_mode_store(struct device *dev, struct device_attribute *attr, > > + const char *buf, size_t count) > > +{ > > + struct scsi_disk *sdkp = to_scsi_disk(dev); > > + > > + if (!capable(CAP_SYS_ADMIN)) > > + return -EACCES; > > + > > + if (!strncmp(buf, zeroing_mode[SD_ZERO_WRITE], 20)) > > + sdkp->zeroing_mode = SD_ZERO_WRITE; > > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS], 20)) > > + sdkp->zeroing_mode = SD_ZERO_WS; > > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS16_UNMAP], 20)) > > + sdkp->zeroing_mode = SD_ZERO_WS16_UNMAP; > > + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS10_UNMAP], 20)) > > + sdkp->zeroing_mode = SD_ZERO_WS10_UNMAP; > > + else > > + return -EINVAL; > > + > > + return count; > > +} > > An additional question about this function: if the shell command "echo" is used > without command-line option -n to modify the "zeroing_mode" sysfs attribute then > a newline character will be present in buf. Does the above code handle newline > characters correctly? It ignores the newlines. But we have a helper called sysfs_streq to possible ignore it. It might be a good idea to move the various sysfs files in scsi to use it.
Bart Van Assche <Bart.VanAssche@sandisk.com> writes: Bart, > characters then zeroing_mode_show() will truncate it. Since all > strings in the zeroing_mode[] array are short, have you considered to > use sprintf() instead? And if you do not want to use sprintf(), how > about using snprintf(buf, PAGE_SIZE, ...)? I'm asking this because I'm > no fan of magic constants. Yeah, this was just a copy and paste from the provisioning code. > Since sysfs guarantees that buf is '\0'-terminated, why does the above > function call strncmp() instead of strcmp()? > > Can the above chain of if-statements be replaced by a for-loop such that > zeroing_mode_store() won't have to be updated if the zeroing_mode[] array > is modified? I have a patch that converts sd.c to sysfs_match_string(). That's much cleaner but will have to wait until the latter gets merged.
diff --git a/drivers/scsi/sd.c b/drivers/scsi/sd.c index bcb0cb020fd2..acf9d17b05d8 100644 --- a/drivers/scsi/sd.c +++ b/drivers/scsi/sd.c @@ -418,6 +418,46 @@ provisioning_mode_store(struct device *dev, struct device_attribute *attr, } static DEVICE_ATTR_RW(provisioning_mode); +static const char *zeroing_mode[] = { + [SD_ZERO_WRITE] = "write", + [SD_ZERO_WS] = "writesame", + [SD_ZERO_WS16_UNMAP] = "writesame_16_unmap", + [SD_ZERO_WS10_UNMAP] = "writesame_10_unmap", +}; + +static ssize_t +zeroing_mode_show(struct device *dev, struct device_attribute *attr, + char *buf) +{ + struct scsi_disk *sdkp = to_scsi_disk(dev); + + return snprintf(buf, 20, "%s\n", zeroing_mode[sdkp->zeroing_mode]); +} + +static ssize_t +zeroing_mode_store(struct device *dev, struct device_attribute *attr, + const char *buf, size_t count) +{ + struct scsi_disk *sdkp = to_scsi_disk(dev); + + if (!capable(CAP_SYS_ADMIN)) + return -EACCES; + + if (!strncmp(buf, zeroing_mode[SD_ZERO_WRITE], 20)) + sdkp->zeroing_mode = SD_ZERO_WRITE; + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS], 20)) + sdkp->zeroing_mode = SD_ZERO_WS; + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS16_UNMAP], 20)) + sdkp->zeroing_mode = SD_ZERO_WS16_UNMAP; + else if (!strncmp(buf, zeroing_mode[SD_ZERO_WS10_UNMAP], 20)) + sdkp->zeroing_mode = SD_ZERO_WS10_UNMAP; + else + return -EINVAL; + + return count; +} +static DEVICE_ATTR_RW(zeroing_mode); + static ssize_t max_medium_access_timeouts_show(struct device *dev, struct device_attribute *attr, char *buf) @@ -496,6 +536,7 @@ static struct attribute *sd_disk_attrs[] = { &dev_attr_app_tag_own.attr, &dev_attr_thin_provisioning.attr, &dev_attr_provisioning_mode.attr, + &dev_attr_zeroing_mode.attr, &dev_attr_max_write_same_blocks.attr, &dev_attr_max_medium_access_timeouts.attr, NULL, @@ -799,10 +840,10 @@ static int sd_setup_write_zeroes_cmnd(struct scsi_cmnd *cmd) u32 nr_sectors = blk_rq_sectors(rq) >> (ilog2(sdp->sector_size) - 9); if (!(rq->cmd_flags & REQ_NOUNMAP)) { - switch (sdkp->provisioning_mode) { - case SD_LBP_WS16: + switch (sdkp->zeroing_mode) { + case SD_ZERO_WS16_UNMAP: return sd_setup_write_same16_cmnd(cmd, true); - case SD_LBP_WS10: + case SD_ZERO_WS10_UNMAP: return sd_setup_write_same10_cmnd(cmd, true); } } @@ -840,6 +881,15 @@ static void sd_config_write_same(struct scsi_disk *sdkp) sdkp->max_ws_blocks = 0; } + if (sdkp->lbprz && sdkp->lbpws) + sdkp->zeroing_mode = SD_ZERO_WS16_UNMAP; + else if (sdkp->lbprz && sdkp->lbpws10) + sdkp->zeroing_mode = SD_ZERO_WS10_UNMAP; + else if (sdkp->max_ws_blocks) + sdkp->zeroing_mode = SD_ZERO_WS; + else + sdkp->zeroing_mode = SD_ZERO_WRITE; + out: blk_queue_max_write_same_sectors(q, sdkp->max_ws_blocks * (logical_block_size >> 9)); diff --git a/drivers/scsi/sd.h b/drivers/scsi/sd.h index 4dac35e96a75..a2c4b5c35379 100644 --- a/drivers/scsi/sd.h +++ b/drivers/scsi/sd.h @@ -59,6 +59,13 @@ enum { SD_LBP_DISABLE, /* Discard disabled due to failed cmd */ }; +enum { + SD_ZERO_WRITE = 0, /* Use WRITE(10/16) command */ + SD_ZERO_WS, /* Use WRITE SAME(10/16) command */ + SD_ZERO_WS16_UNMAP, /* Use WRITE SAME(16) with UNMAP */ + SD_ZERO_WS10_UNMAP, /* Use WRITE SAME(10) with UNMAP */ +}; + struct scsi_disk { struct scsi_driver *driver; /* always &sd_template */ struct scsi_device *device; @@ -89,6 +96,7 @@ struct scsi_disk { u8 write_prot; u8 protection_type;/* Data Integrity Field */ u8 provisioning_mode; + u8 zeroing_mode; unsigned ATO : 1; /* state of disk ATO bit */ unsigned cache_override : 1; /* temp override of WCE,RCD */ unsigned WCE : 1; /* state of disk WCE bit */
Now that zeroout and discards are distinct operations we need to separate the policy of choosing the appropriate command. Create a zeroing_mode which can be one of: write: Zeroout assist not present, use regular WRITE writesame: Allow WRITE SAME(10/16) with a zeroed payload writesame_16_unmap: Allow WRITE SAME(16) with UNMAP writesame_10_unmap: Allow WRITE SAME(10) with UNMAP The last two are conditional on the device being thin provisioned with LBPRZ=1 and LBPWS=1 or LBPWS10=1 respectively. Whether to set the UNMAP bit or not depends on the REQ_NOUNMAP flag. And if none of the _unmap variants are supported, regular WRITE SAME will be used if the device supports it. The zeroout_mode is exported in sysfs and the detected mode for a given device can be overridden using the string constants above. With this change in place we can now issue WRITE SAME(16) with UNMAP set for block zeroing applications that require hard guarantees and logical_block_size granularity. And at the same time use the UNMAP command with the device's preferred granulary and alignment for discard operations. Cc: Christoph Hellwig <hch@lst.de> Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com> --- drivers/scsi/sd.c | 56 ++++++++++++++++++++++++++++++++++++++++++++++++++++--- drivers/scsi/sd.h | 8 ++++++++ 2 files changed, 61 insertions(+), 3 deletions(-)