I support this addition as it can be done without the module reload
provided by my prior patch.
Reviewed-by: Laurence Oberman <oberman.l@xxxxxxxxx>
On Mon, Oct 12, 2015 at 12:31 AM, Seymour, Shane M
<shane.seymour@xxxxxxx> wrote:
>
> 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@xxxxxxx>
> ---
> --- a/drivers/scsi/st.c 2015-10-06 17:11:16.299801789 -0500
> +++ b/drivers/scsi/st.c 2015-10-11 14:45:10.595060995 -0500
> @@ -4452,11 +4452,41 @@ static ssize_t version_show(struct devic
> }
> 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);
> diff -uprN a/Documentation/ABI/testing/sysfs-driver-st b/Documentation/ABI/testing/sysfs-driver-st
> --- a/Documentation/ABI/testing/sysfs-driver-st 1969-12-31 18:00:00.000000000 -0600
> +++ b/Documentation/ABI/testing/sysfs-driver-st 2015-10-11 14:28:43.537128220 -0500
> @@ -0,0 +1,12 @@
> +What: /sys/bus/scsi/drivers/st/debug_flag
> +Date: October 2015
> +Kernel Version: ?.?
> +Contact: shane.seymour@xxxxxxx
> +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.
> --- a/Documentation/scsi/st.txt 2015-10-06 17:11:12.323802060 -0500
> +++ b/Documentation/scsi/st.txt 2015-10-11 14:19:48.176164681 -0500
> @@ -569,7 +569,9 @@ Debugging code is now compiled in by def
> 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
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