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scsi: st: Add sysfs file position_lost_in_reset 

If the value read from the file is 1, reads and writes from/to the device
are blocked because the tape position may not match user's expectation
(tape rewound after device reset).

Signed-off-by: Kai Mäkisara <Kai.Makisara@kolumbus.fi>
Link: https://lore.kernel.org/r/20250201151106.25529-1-Kai.Makisara@kolumbus.fi
Reviewed-by: John Meneghini <jmeneghi@redhat.com>
Tested-by: John Meneghini <jmeneghi@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Kai Mäkisara 2025-02-01 17:11:06 +02:00 committed by Martin K. Petersen
parent 341128dfe1
commit 2c445d5f83
2 changed files with 24 additions and 0 deletions
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5
Documentation/scsi/st.rst
View File

@ -157,6 +157,11 @@ enabled driver and mode options. The value in the file is a bit mask where the
bit definitions are the same as those used with MTSETDRVBUFFER in setting the
options.
Each directory contains the entry 'position_lost_in_reset'. If this value is
one, reading and writing to the device is blocked after device reset. Most
devices rewind the tape after reset and the writes/read don't access the
tape position the user expects.
A link named 'tape' is made from the SCSI device directory to the class
directory corresponding to the mode 0 auto-rewind device (e.g., st0).

19
drivers/scsi/st.c
View File

@ -4703,6 +4703,24 @@ options_show(struct device *dev, struct device_attribute *attr, char *buf)
}
static DEVICE_ATTR_RO(options);
/**
* position_lost_in_reset_show - Value 1 indicates that reads, writes, etc.
* are blocked because a device reset has occurred and no operation positioning
* the tape has been issued.
* @dev: struct device
* @attr: attribute structure
* @buf: buffer to return formatted data in
*/
static ssize_t position_lost_in_reset_show(struct device *dev,
struct device_attribute *attr, char *buf)
{
struct st_modedef *STm = dev_get_drvdata(dev);
struct scsi_tape *STp = STm->tape;
return sprintf(buf, "%d", STp->pos_unknown);
}
static DEVICE_ATTR_RO(position_lost_in_reset);
/* Support for tape stats */
/**
@ -4887,6 +4905,7 @@ static struct attribute *st_dev_attrs[] = {
&dev_attr_default_density.attr,
&dev_attr_default_compression.attr,
&dev_attr_options.attr,
&dev_attr_position_lost_in_reset.attr,
NULL,
};