diff options
authorSeymour, Shane M <shane.seymour@hpe.com>2015-10-12 04:31:17 +0000
committerJames Bottomley <JBottomley@Odin.com>2015-11-09 17:17:27 -0800
commitd9b43a10f0d04564c6e05de3728c3cbba64c644d (patch)
parentc59ab4e5afade13fdb65efc99c07fb8455aecba5 (diff)
st: allow debug output to be enabled or disabled via sysfs
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@hpe.com> Reviewed-by: Laurence Oberman <oberman.l@gmail.com> Acked-by: Kai Mäkisara <kai.makisara@kolumbus.fi> Signed-off-by: James Bottomley <JBottomley@Odin.com>
3 files changed, 45 insertions, 1 deletions
diff --git a/Documentation/ABI/testing/sysfs-driver-st b/Documentation/ABI/testing/sysfs-driver-st
new file mode 100644
index 000000000000..ba5d77008a85
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-st
@@ -0,0 +1,12 @@
+What: /sys/bus/scsi/drivers/st/debug_flag
+Date: October 2015
+Kernel Version: ?.?
+Contact: shane.seymour@hpe.com
+ 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.
diff --git a/Documentation/scsi/st.txt b/Documentation/scsi/st.txt
index f29fa550665a..b3211af63b79 100644
--- a/Documentation/scsi/st.txt
+++ b/Documentation/scsi/st.txt
@@ -569,7 +569,9 @@ Debugging code is now compiled in by default but debugging is turned off
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
diff --git a/drivers/scsi/st.c b/drivers/scsi/st.c
index b37b9b00c4b4..e0a1e52a04e7 100644
--- a/drivers/scsi/st.c
+++ b/drivers/scsi/st.c
@@ -4452,11 +4452,41 @@ static ssize_t version_show(struct device_driver *ddd, char *buf)
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);
static struct attribute *st_drv_attrs[] = {
+#if DEBUG
+ &driver_attr_debug_flag.attr,

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