scsi: target: Fix the pgr/alua_support_store functions

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2023439

Commit 356ba2a8 ("scsi: target: tcmu: Make pgr_support and alua_support attributes writable") introduced support for changeable alua_support and pgr_support target attributes. These can only be changed if the backstore is user-backed, otherwise the kernel returns -EINVAL.

This triggers a warning in the targetcli/rtslib code when performing a target restore that includes non-userbacked backstores:

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 code only if we are really going to flip the PGR/ALUA bit in the transport_flags field, otherwise we will do nothing and return success.

Return ENOSYS instead of EINVAL if the pgr/alua attributes can not be changed, this way it will 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.

Fixes: 356ba2a8 ("scsi: target: tcmu: Make pgr_support and alua_support attributes writable") Link: https://lore.kernel.org/r/20210906151809.52811-1-mlombard@redhat.com Reviewed-by: Bodo Stroesser bostroesser@gmail.com Signed-off-by: Maurizio Lombardi mlombard@redhat.com Signed-off-by: Martin K. Petersen martin.petersen@oracle.com (cherry picked from commit ef7ae7f746e95c6fa4ec2bcfacb949c36263da78) Signed-off-by: Maurizio Lombardi mlombard@redhat.com