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Commit d9b43a10 authored by Seymour, Shane M's avatar Seymour, Shane M Committed by James Bottomley
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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: default avatarShane Seymour <shane.seymour@hpe.com>
Reviewed-by: default avatarLaurence Oberman <oberman.l@gmail.com>
Acked-by: default avatarKai Mäkisara <kai.makisara@kolumbus.fi>
Signed-off-by: default avatarJames Bottomley <JBottomley@Odin.com>
parent c59ab4e5

Documentation/ABI/testing/sysfs-driver-st

0 → 100644
+12 −0
Original line number Diff line number Diff line 
What:		/sys/bus/scsi/drivers/st/debug_flag

Date:		October 2015

Kernel Version:	?.?

Contact:	shane.seymour@hpe.com

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.

Documentation/scsi/st.txt

+3 −1
Original line number Diff line number Diff line
@@ -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

drivers/scsi/st.c

+30 −0
Original line number Diff line number Diff line
@@ -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);

#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);