Re: [PATCHv8 20/23] scsi: Add 'access_state' attribute

[Hannes Reinecke <hare@suse.de>]

On 02/19/2016 08:10 PM, Bart Van Assche wrote:
> On 02/19/2016 12:17 AM, Hannes Reinecke wrote:
>> +static ssize_t
>> +sdev_show_access_state(struct device *dev,
>> +		       struct device_attribute *attr,
>> +		       char *buf)
>> +{
>> +	struct scsi_device *sdev = to_scsi_device(dev);
>> +	unsigned char access_state;
>> +	const char *access_state_name;
>> +	bool pref = false;
>> +
>> +	if (!sdev->handler)
>> +		return -EINVAL;
>> +
>> +	if (sdev->access_state & SCSI_ACCESS_STATE_PREFERRED)
>> +		pref = true;
>> +
>> +	access_state = (sdev->access_state & SCSI_ACCESS_STATE_MASK);
>> +	access_state_name = scsi_access_state_name(access_state);
>> +
>> +	return snprintf(buf, 32, "%s%s\n",
>> +			access_state_name ? access_state_name : "unknown",
>> +			pref ? " preferred" : "");
>> +}
>
> Hello Hannes,
>
> What is inelegant about the above approach is that the access_state attribute
> is added to all SCSI devices, whether or not a device handler has been attached,
> and that reading that attribute doesn't fail for devices to which another handler
> than the ALUA handler has been attached. How about the patch below, which moves
> the access_state show handler to the scsi_dh_alua.c source file, where it belongs?
>
Actually, this was my first approach, but hch suggested moving it to
the generic code :-(

Also when using your suggestion the 'access_state' attribute will only 
be created _after_ the 'ADD' uevent, making it impossible to use it from 
udev events.

However, I'm currently working on using the 'is_visible' callback for 
SCSI sysfs attributes for this; in theory it should be possible to
use 'sysfs_update_groups()' during scsi_add_lun() to blank out the
unsupported attributes.

Which I think might be the best approach here.

But probably not for this patch series; I'd rather have the alua update 
in first as it took long enough.

If you're absolutely against it we can drop the 'access_state' patches
(ie patch 20-22) and have them folded into a separate patchset.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@suse.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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