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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 <[email protected]>
Reviewed-by: Laurence Oberman <[email protected]>
Acked-by: Kai Mäkisara <[email protected]>
Signed-off-by: James Bottomley <[email protected]>
This commit is contained in:
Seymour, Shane M 2015-10-12 04:31:17 +00:00 • committed by James Bottomley
commit d9b43a10f0
3 changed files with 45 additions and 1 deletions
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4
Documentation/scsi/st.txt
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@ -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