[SCSI] scsi_dh: Add 'dh_state' sysfs attribute

Implement a 'dh_state' sdev attribute for dynamic device handler
manipulation. A read on the attribute will return the name of
the currently attached device handler or 'detached' if no handler
is attached.
The attribute allows the following strings to be written:
- The name of the device handler to be attached if the state is
  'detached'.
- 'activate' to trigger path activation if a device handler
  is attached.
- 'detach' to detach the currently attached device handler.

Signed-off-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Chandra Seetharaman <sekharan@us.ibm.com>
Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>

1 files changed, 102 insertions, 1 deletions

diff --git a/drivers/scsi/device_handler/scsi_dh.c b/drivers/scsi/device_handler/scsi_dh.c
index 3f798171ed69..e90df9dd3e65 100644
--- a/drivers/scsi/device_handler/scsi_dh.c
+++ b/drivers/scsi/device_handler/scsi_dh.c
@@ -84,7 +84,7 @@ static int scsi_dh_handler_attach(struct scsi_device *sdev,
  * @scsi_dh - Device handler to be detached
  *
  * Detach from a device handler. If a device handler is specified,
- * only detach if the currently attached handler is equal to it.
+ * only detach if the currently attached handler matches @scsi_dh.
  */
 static void scsi_dh_handler_detach(struct scsi_device *sdev,
                                    struct scsi_device_handler *scsi_dh)
@@ -103,6 +103,98 @@ static void scsi_dh_handler_detach(struct scsi_device *sdev,
 }
 
 /*
+ * Functions for sysfs attribute 'dh_state'
+ */
+static ssize_t
+store_dh_state(struct device *dev, struct device_attribute *attr,
+               const char *buf, size_t count)
+{
+        struct scsi_device *sdev = to_scsi_device(dev);
+        struct scsi_device_handler *scsi_dh;
+        int err = -EINVAL;
+
+        if (!sdev->scsi_dh_data) {
+                /*
+                 * Attach to a device handler
+                 */
+                if (!(scsi_dh = get_device_handler(buf)))
+                        return err;
+                err = scsi_dh_handler_attach(sdev, scsi_dh);
+        } else {
+                scsi_dh = sdev->scsi_dh_data->scsi_dh;
+                if (!strncmp(buf, "detach", 6)) {
+                        /*
+                         * Detach from a device handler
+                         */
+                        scsi_dh_handler_detach(sdev, scsi_dh);
+                        err = 0;
+                } else if (!strncmp(buf, "activate", 8)) {
+                        /*
+                         * Activate a device handler
+                         */
+                        if (scsi_dh->activate)
+                                err = scsi_dh->activate(sdev);
+                        else
+                                err = 0;
+                }
+        }
+
+        return err<0?err:count;
+}
+
+static ssize_t
+show_dh_state(struct device *dev, struct device_attribute *attr, char *buf)
+{
+        struct scsi_device *sdev = to_scsi_device(dev);
+
+        if (!sdev->scsi_dh_data)
+                return snprintf(buf, 20, "detached\n");
+
+        return snprintf(buf, 20, "%s\n", sdev->scsi_dh_data->scsi_dh->name);
+}
+
+static struct device_attribute scsi_dh_state_attr =
+        __ATTR(dh_state, S_IRUGO | S_IWUSR, show_dh_state,
+               store_dh_state);
+
+/*
+ * scsi_dh_sysfs_attr_add - Callback for scsi_init_dh
+ */
+static int scsi_dh_sysfs_attr_add(struct device *dev, void *data)
+{
+        struct scsi_device *sdev;
+        int err;
+
+        if (!scsi_is_sdev_device(dev))
+                return 0;
+
+        sdev = to_scsi_device(dev);
+
+        err = device_create_file(&sdev->sdev_gendev,
+                                 &scsi_dh_state_attr);
+
+        return 0;
+}
+
+/*
+ * scsi_dh_sysfs_attr_remove - Callback for scsi_exit_dh
+ */
+static int scsi_dh_sysfs_attr_remove(struct device *dev, void *data)
+{
+        struct scsi_device *sdev;
+
+        if (!scsi_is_sdev_device(dev))
+                return 0;
+
+        sdev = to_scsi_device(dev);
+
+        device_remove_file(&sdev->sdev_gendev,
+                           &scsi_dh_state_attr);
+
+        return 0;
+}
+
+/*
  * scsi_dh_notifier - notifier chain callback
  */
 static int scsi_dh_notifier(struct notifier_block *nb,
@@ -132,7 +224,10 @@ static int scsi_dh_notifier(struct notifier_block *nb,
 
         if (action == BUS_NOTIFY_ADD_DEVICE) {
                 err = scsi_dh_handler_attach(sdev, devinfo);
+                if (!err)
+                        err = device_create_file(dev, &scsi_dh_state_attr);
         } else if (action == BUS_NOTIFY_DEL_DEVICE) {
+                device_remove_file(dev, &scsi_dh_state_attr);
                 scsi_dh_handler_detach(sdev, NULL);
         }
 out:
@@ -284,11 +379,17 @@ static int __init scsi_dh_init(void)
 
         r = bus_register_notifier(&scsi_bus_type, &scsi_dh_nb);
 
+        if (!r)
+                bus_for_each_dev(&scsi_bus_type, NULL, NULL,
+                                 scsi_dh_sysfs_attr_add);
+
         return r;
 }
 
 static void __exit scsi_dh_exit(void)
 {
+        bus_for_each_dev(&scsi_bus_type, NULL, NULL,
+                         scsi_dh_sysfs_attr_remove);
         bus_unregister_notifier(&scsi_bus_type, &scsi_dh_nb);
 }