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st: allow debug output to be enabled or disabled via sysfs

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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>
This commit is contained in:
Seymour, Shane M
2015-10-12 04:31:17 +00:00
committed by James Bottomley
parent c59ab4e5af
commit d9b43a10f0
3 changed files with 45 additions and 1 deletions
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12
Documentation/ABI/testing/sysfs-driver-st Normal file
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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.