block: restore original behavior of /proc/partition when there's no partition

/proc/partitions didn't use to write out the header if there was no
partition.  However, recent commit 66c64afe changed the behavior.
This is nothing major but there's no reason to change user visible
behavior without a good rationale.  Restore the original behavior.

Note that 2.6.28 has clean up changes scheduled which will replace
this rather hacky implementation.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Greg KH <greg@kroah.com>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

block/genhd.c

@@ -307,7 +307,7 @@ static void *part_start(struct seq_file *part, loff_t *pos)
 	loff_t k = *pos;
 
 	if (!k)
-		seq_puts(part, "major minor  #blocks  name\n\n");
+		part->private = (void *)1LU;	/* tell show to print header */
 
 	mutex_lock(&block_class_lock);
 	dev = class_find_device(&block_class, NULL, &k, find_start);
@@ -349,6 +349,17 @@ static int show_partition(struct seq_file *part, void *v)
 	int n;
 	char buf[BDEVNAME_SIZE];
 
+	/*
+	 * Print header if start told us to do.  This is to preserve
+	 * the original behavior of not printing header if no
+	 * partition exists.  This hackery will be removed later with
+	 * class iteration clean up.
+	 */
+	if (part->private) {
+		seq_puts(part, "major minor  #blocks  name\n\n");
+		part->private = NULL;
+	}
+
 	/* Don't show non-partitionable removeable devices or empty devices */
 	if (!get_capacity(sgp) ||
 			(sgp->minors == 1 && (sgp->flags & GENHD_FL_REMOVABLE)))