[2.5.75] fix removable partitioned media with devfs

Current 2.5 does not register any device node in devfs for empty media (capacity == 0) case. This makes removables unusable with devfs. Partition rescan is done only on bdev open, but without any device node for device it is impossible to open it.

In 2.4 it was finally solved by always registering .../disc node as representation for "whole" disk and using devfsd action to force partition rescan on access to (non-existing) partition name. For primary names it was handled internally by devfs - it kept track of removable devices in directory and initiated partition rescan when name was not found.

Both are obviously broken now. You can't do partition rescan because no node is registered at all and internal handling was removed. Very nice.

The attached patch makes resgister_disk always register at least disc node. This now works for old and new compat names as per devfsd configuration; canonical names are still broken:

{pts/3}% ll /dev/scsi/host1/bus0/target4/lun0/part4
ls: /dev/scsi/host1/bus0/target4/lun0/part4: No such file or directory

but it can be fixed using the same technique as above so I won't push it.

-andrey

@@ -348,6 +348,9 @@ void register_disk(struct gendisk *disk)
 		return;
 	}
 
+	/* always add handle for the whole disk */
+	devfs_add_partitioned(disk);
+
 	/* No such device (e.g., media were just removed) */
 	if (!get_capacity(disk))
 		return;

@@ -356,7 +359,6 @@ void register_disk(struct gendisk *disk)
 	if (blkdev_get(bdev, FMODE_READ, 0, BDEV_RAW) < 0)
 		return;
 	state = check_partition(disk, bdev);
-	devfs_add_partitioned(disk);
 	if (state) {
 		for (j = 1; j < state->limit; j++) {
 			sector_t size = state->parts[j].size;