[v3b,4/4] scsi: st: Add sysfs file position_lost_in_reset

Commit Message

Kai Mäkisara Feb. 1, 2025, 3:11 p.m. UTC

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 <[e-mail]>
Reviewed-by: John Meneghini <[e-mail]>
Tested-by: John Meneghini <[e-mail]>
---

Changed in v3b:
- sysfs file name has been changed to position_lost_in_reset

---
 Documentation/scsi/st.rst |  5 +++++
 drivers/scsi/st.c         | 19 +++++++++++++++++++
 2 files changed, 24 insertions(+)

Patch

diff --git a/Documentation/scsi/st.rst b/Documentation/scsi/st.rst
index d3b28c28d74c..b4a092faa9c8 100644
--- a/Documentation/scsi/st.rst
+++ b/Documentation/scsi/st.rst
@@ -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).
 
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index 6ec1cfeb92ff..85867120c8a9 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -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,
 };