Change st driver to allow enabling or disabling debug output
via sysfs file /sys/bus/scsi/drivers/st/debug_flag.
Previously the only way to enable debug output was:
1. loading the driver with the module parameter debug_flag=1
2. an ioctl call (this method was also the only way to dynamically
disable debug output).
To use the ioctl you need a second tape drive (if you are
actively testing the first tape drive) since a second process
cannot open the first tape drive if it is in use.
The this change is only functional if the value of the macro
DEBUG in st.c is a non-zero value (which it is by default).
Signed-off-by: Shane Seymour <shane.seymour@xxxxxxx>
---
--- a/drivers/scsi/st.c 2015-10-06 17:11:16.299801789 -0500
+++ b/drivers/scsi/st.c 2015-10-11 14:45:10.595060995 -0500
@@ -4452,11 +4452,41 @@ static ssize_t version_show(struct devic
}
static DRIVER_ATTR_RO(version);
+#if DEBUG
+static ssize_t debug_flag_store(struct device_driver *ddp,
+ const char *buf, size_t count)
+{
+/* We only care what the first byte of the data is the rest is unused.
+ * if it's a '1' we turn on debug and if it's a '0' we disable it. All
+ * other values have -EINVAL returned if they are passed in.
+ */
+ if (count > 0) {
+ if (buf[0] == '0') {
+ debugging = NO_DEBUG;
+ return count;
+ } else if (buf[0] == '1') {
+ debugging = 1;
+ return count;
+ }
+ }
+ return -EINVAL;
+}
+
+static ssize_t debug_flag_show(struct device_driver *ddp, char *buf)
+{
+ return scnprintf(buf, PAGE_SIZE, "%d\n", debugging);
+}
+static DRIVER_ATTR_RW(debug_flag);
+#endif
+
static struct attribute *st_drv_attrs[] = {
&driver_attr_try_direct_io.attr,
&driver_attr_fixed_buffer_size.attr,
&driver_attr_max_sg_segs.attr,
&driver_attr_version.attr,
+#if DEBUG
+ &driver_attr_debug_flag.attr,
+#endif
NULL,
};
ATTRIBUTE_GROUPS(st_drv);
diff -uprN a/Documentation/ABI/testing/sysfs-driver-st b/Documentation/ABI/testing/sysfs-driver-st
--- a/Documentation/ABI/testing/sysfs-driver-st 1969-12-31 18:00:00.000000000 -0600
+++ b/Documentation/ABI/testing/sysfs-driver-st 2015-10-11 14:28:43.537128220 -0500
@@ -0,0 +1,12 @@
+What: /sys/bus/scsi/drivers/st/debug_flag
+Date: October 2015
+Kernel Version: ?.?
+Contact: shane.seymour@xxxxxxx
+Description:
+ This file allows you to turn debug output from the st driver
+ off if you write a '0' to the file or on if you write a '1'.
+ Note that debug output requires that the module be compiled
+ with the #define DEBUG set to a non-zero value (this is the
+ default). If DEBUG is set to 0 then this file will not
+ appear in sysfs as its presence is conditional upon debug
+ output support being compiled into the module.
--- a/Documentation/scsi/st.txt 2015-10-06 17:11:12.323802060 -0500
+++ b/Documentation/scsi/st.txt 2015-10-11 14:19:48.176164681 -0500
@@ -569,7 +569,9 @@ Debugging code is now compiled in by def
with the kernel module parameter debug_flag defaulting to 0. Debugging
can still be switched on and off with an ioctl. To enable debug at
module load time add debug_flag=1 to the module load options, the
-debugging output is not voluminous.
+debugging output is not voluminous. Debugging can also be enabled
+and disabled by writing a '0' (disable) or '1' (enable) to the sysfs
+file /sys/bus/scsi/drivers/st/debug_flag.
If the tape seems to hang, I would be very interested to hear where
the driver is waiting. With the command 'ps -l' you can see the state
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