scsi: target: tcmu: Make pgr_support and alua_support attributes writable

Currently in tcmu reservation commands are handled by core's pr
implementation (default) or completely rejected (emulate_pr set to 0). We
additionally want to be able to do full reservation handling in
userspace. Therefore we need a way to set TRANSPORT_FLAG_PASSTHROUGH_PGR.

The inverted flag is displayed by attribute pgr_support. Since we moved
the flag from transport/backend to se_device in the previous commit, we now
can make it changeable per device by allowing to write the attribute. The
new field transport_flags_changeable in transport/backend is used to reject
writing if not allowed for a backend.

Regarding ALUA we also want to be able to passthrough commands to userspace
in tcmu. Therefore we need TRANSPORT_FLAG_PASSTHROUGH_ALUA to be
changeable, because by setting it we can switch off all ALUA checks in
core. So we also set TRANSPORT_FLAG_PASSTHROUGH_ALUA in tcmu's
transport_flags_changeable.

Of course, ALUA and reservation handling in userspace will work only, if
session/nexus information is sent to userspace along with every
command. This will be object of a patch series announced by Mike Christie.

Link: https://lore.kernel.org/r/[e-mail]
Reviewed-by: Mike Christie <[e-mail]>
Signed-off-by: Bodo Stroesser <[e-mail]>
Signed-off-by: Martin K. Petersen <[e-mail]>

drivers/target/target_core_configfs.c

···
 			flags & TRANSPORT_FLAG_PASSTHROUGH_ALUA ? 0 : 1);
 }
 
+static ssize_t alua_support_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct se_dev_attrib *da = to_attrib(item);
+	struct se_device *dev = da->da_dev;
+	bool flag;
+	int ret;
+
+	if (!(dev->transport->transport_flags_changeable &
+	      TRANSPORT_FLAG_PASSTHROUGH_ALUA)) {
+		pr_err("dev[%p]: Unable to change SE Device alua_support:"
+			" alua_support has fixed value\n", dev);
+		return -EINVAL;
+	}
+
+	ret = strtobool(page, &flag);
+	if (ret < 0)
+		return ret;
+
+	if (flag)
+		dev->transport_flags &= ~TRANSPORT_FLAG_PASSTHROUGH_ALUA;
+	else
+		dev->transport_flags |= TRANSPORT_FLAG_PASSTHROUGH_ALUA;
+	return count;
+}
+
 static ssize_t pgr_support_show(struct config_item *item, char *page)
 {
 	struct se_dev_attrib *da = to_attrib(item);
···
 
 	return snprintf(page, PAGE_SIZE, "%d\n",
 			flags & TRANSPORT_FLAG_PASSTHROUGH_PGR ? 0 : 1);
+}
+
+static ssize_t pgr_support_store(struct config_item *item,
+		const char *page, size_t count)
+{
+	struct se_dev_attrib *da = to_attrib(item);
+	struct se_device *dev = da->da_dev;
+	bool flag;
+	int ret;
+
+	if (!(dev->transport->transport_flags_changeable &
+	      TRANSPORT_FLAG_PASSTHROUGH_PGR)) {
+		pr_err("dev[%p]: Unable to change SE Device pgr_support:"
+			" pgr_support has fixed value\n", dev);
+		return -EINVAL;
+	}
+
+	ret = strtobool(page, &flag);
+	if (ret < 0)
+		return ret;
+
+	if (flag)
+		dev->transport_flags &= ~TRANSPORT_FLAG_PASSTHROUGH_PGR;
+	else
+		dev->transport_flags |= TRANSPORT_FLAG_PASSTHROUGH_PGR;
+	return count;
 }
 
 CONFIGFS_ATTR(, emulate_model_alias);
···
 CONFIGFS_ATTR(, unmap_granularity_alignment);
 CONFIGFS_ATTR(, unmap_zeroes_data);
 CONFIGFS_ATTR(, max_write_same_len);
-CONFIGFS_ATTR_RO(, alua_support);
-CONFIGFS_ATTR_RO(, pgr_support);
+CONFIGFS_ATTR(, alua_support);
+CONFIGFS_ATTR(, pgr_support);
 
 /*
  * dev_attrib attributes for devices using the target core SBC/SPC

drivers/target/target_core_user.c

···
 	.name			= "user",
 	.owner			= THIS_MODULE,
 	.transport_flags_default = TRANSPORT_FLAG_PASSTHROUGH,
+	.transport_flags_changeable = TRANSPORT_FLAG_PASSTHROUGH_PGR |
+				      TRANSPORT_FLAG_PASSTHROUGH_ALUA,
 	.attach_hba		= tcmu_attach_hba,
 	.detach_hba		= tcmu_detach_hba,
 	.alloc_device		= tcmu_alloc_device,

include/target/target_core_backend.h

···
 	struct module *owner;
 
 	u8 transport_flags_default;
+	u8 transport_flags_changeable;
 
 	int (*attach_hba)(struct se_hba *, u32);
 	void (*detach_hba)(struct se_hba *);