[RFC] scsi: make "access_state" sysfs attribute always visible

From: Martin Wilck <mwilck@suse.com>

If a SCSI device handler module is loaded after some SCSI devices
have already been probed (e.g. via request_module() by dm-multipath),
the "access_state" and "preferred_path" sysfs attributes remain invisible for
these devices, although the handler is attached and live. The reason is
that the visibility is only checked when the sysfs attribute group is
first created. This results in an inconsistent user experience depending
on the load order of SCSI low-level drivers vs. device handler modules.

This patch changes user space API: attempting to read the "access_state"
or "preferred_path" attributes will now result in -EINVAL rather than
-ENODEV for devices that have no device handler, and tests for the existence
of these attributes will have a different result.

Signed-off-by: Martin Wilck <mwilck@suse.com>
---
 drivers/scsi/scsi_sysfs.c | 8 --------
 1 file changed, 8 deletions(-)

On 1/27/22 18:28, Bart Van Assche wrote:
> On 1/25/22 08:24, mwilck@suse.com wrote:
>> From: Martin Wilck <mwilck@suse.com>
>>
>> If a SCSI device handler module is loaded after some SCSI devices
>> have already been probed (e.g. via request_module() by dm-multipath),
>> the "access_state" and "preferred_path" sysfs attributes remain 
>> invisible for
>> these devices, although the handler is attached and live. The reason is
>> that the visibility is only checked when the sysfs attribute group is
>> first created. This results in an inconsistent user experience depending
>> on the load order of SCSI low-level drivers vs. device handler modules.
> 
> Isn't this something that should be fixed in the sysfs code rather than 
> in the SCSI core? If this issue affects SCSI I assume that it will also 
> affect other sysfs users.
> 
Urgh.
Rather not.
That particular code affects the visibility of sysfs attributes; they 
are created statically in device_add(), so it won't even be created if 
it's not visible.

Reworking that would mean a rework of the entire drivers/base code.
And not to mention a change in behaviour, as some drivers might well 
rely on the current behaviour.

But if you feel up to it ...

Cheers,

Hannes

On 25.01.22 18:24, mwilck@suse.com wrote:
> From: Martin Wilck <mwilck@suse.com>
> 
> If a SCSI device handler module is loaded after some SCSI devices
> have already been probed (e.g. via request_module() by dm-multipath),
> the "access_state" and "preferred_path" sysfs attributes remain invisible for
> these devices, although the handler is attached and live. The reason is
> that the visibility is only checked when the sysfs attribute group is
> first created. This results in an inconsistent user experience depending
> on the load order of SCSI low-level drivers vs. device handler modules.
> 

I suppose you looked at sysfs_update_group(), and it's not a good fit?

> This patch changes user space API: attempting to read the "access_state"
> or "preferred_path" attributes will now result in -EINVAL rather than
> -ENODEV for devices that have no device handler, and tests for the existence
> of these attributes will have a different result.
> 
> Signed-off-by: Martin Wilck <mwilck@suse.com>
> ---
>  drivers/scsi/scsi_sysfs.c | 8 --------
>  1 file changed, 8 deletions(-)
> 
> diff --git a/drivers/scsi/scsi_sysfs.c b/drivers/scsi/scsi_sysfs.c
> index f1e0c131b77c..226a50944c00 100644
> --- a/drivers/scsi/scsi_sysfs.c
> +++ b/drivers/scsi/scsi_sysfs.c
> @@ -1228,14 +1228,6 @@ static umode_t scsi_sdev_attr_is_visible(struct kobject *kobj,
>  	    !sdev->host->hostt->change_queue_depth)
>  		return 0;
>  
> -#ifdef CONFIG_SCSI_DH
> -	if (attr == &dev_attr_access_state.attr &&
> -	    !sdev->handler)
> -		return 0;
> -	if (attr == &dev_attr_preferred_path.attr &&
> -	    !sdev->handler)
> -		return 0;
> -#endif
>  	return attr->mode;
>  }
>  

]