Re: [PATCH] target: fix the pgr/alua_support_store functions

[michael.christie@oracle.com]

On 9/3/21 7:48 AM, Maurizio Lombardi wrote:
> Commit 356ba2a8bc8d ("scsi: target: tcmu: Make pgr_support and
> alua_support attributes writable")
> introduced support for changeable alua_support and pgr_support
> target attributes. They can only be changed
> if the backstore is user-backed, otherwise the kernel returns -EINVAL.
> 
> This caused a regression in targetcli/rtslib because now a warning
> is triggered when performing a target restore that includes
> non-userbacked backstores, even if rtslib is not trying to change
> the attributes' values:
> 
> $ targetctl restore
> Storage Object block/storage1: Cannot set attribute alua_support:
> [Errno 22] Invalid argument, skipped
> Storage Object block/storage1: Cannot set attribute pgr_support:
> [Errno 22] Invalid argument, skipped
> 
> Fix this warning by returning an error only if we are really
> going to flip the PGR/ALUA bit in the transport_flags field,
> otherwise we'll do nothing and return success.
> 
> Return EOPNOTSUPP instead of EINVAL if the pgr/alua attributes
> can't be changed, this way it'll be possible for userspace to understand
> if the operation failed because an invalid value has been passed
> to strtobool() or because the attributes are fixed.

Maybe you want to use -ENOSYS. Other lio sysfs files return that when the
operation is not supported. You could then handle all the warnings with
the same check.