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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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30
drivers/scsi/st.c
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@ -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);