btrfs: split write_dev_supers to two functions

There are two independent parts, one that writes the superblocks and
another that waits for completion. No functional changes, but cleanups,
reformatting and comment updates.
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/disk-io.c

@@ -3373,19 +3373,17 @@ struct buffer_head *btrfs_read_dev_super(struct block_device *bdev)
 }
 
 /*
- * this should be called twice, once with wait == 0 and
- * once with wait == 1.  When wait == 0 is done, all the buffer heads
- * we write are pinned.
+ * Write superblock @sb to the @device. Do not wait for completion, all the
+ * buffer heads we write are pinned.
  *
- * They are released when wait == 1 is done.
- * max_mirrors must be the same for both runs, and it indicates how
- * many supers on this one device should be written.
+ * Write @max_mirrors copies of the superblock, where 0 means default that fit
+ * the expected device size at commit time. Note that max_mirrors must be
+ * same for write and wait phases.
  *
- * max_mirrors == 0 means to write them all.
+ * Return number of errors when buffer head is not found or submission fails.
  */
 static int write_dev_supers(struct btrfs_device *device,
-			    struct btrfs_super_block *sb,
-			    int wait, int max_mirrors)
+			    struct btrfs_super_block *sb, int max_mirrors)
 {
 	struct buffer_head *bh;
 	int i;
@@ -3403,37 +3401,14 @@ static int write_dev_supers(struct btrfs_device *device,
 		    device->commit_total_bytes)
 			break;
 
-		if (wait) {
-			bh = __find_get_block(device->bdev, bytenr / 4096,
-					      BTRFS_SUPER_INFO_SIZE);
-			if (!bh) {
-				errors++;
-				continue;
-			}
-			wait_on_buffer(bh);
-			if (!buffer_uptodate(bh))
-				errors++;
-
-			/* drop our reference */
-			brelse(bh);
-
-			/* drop the reference from the wait == 0 run */
-			brelse(bh);
-			continue;
-		} else {
 		btrfs_set_super_bytenr(sb, bytenr);
 
 		crc = ~(u32)0;
-			crc = btrfs_csum_data((const char *)sb +
-					      BTRFS_CSUM_SIZE, crc,
-					      BTRFS_SUPER_INFO_SIZE -
-					      BTRFS_CSUM_SIZE);
+		crc = btrfs_csum_data((const char *)sb + BTRFS_CSUM_SIZE, crc,
+				      BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
 		btrfs_csum_final(crc, sb->csum);
 
-			/*
-			 * one reference for us, and we leave it for the
-			 * caller
-			 */
+		/* One reference for us, and we leave it for the caller */
 		bh = __getblk(device->bdev, bytenr / 4096,
 			      BTRFS_SUPER_INFO_SIZE);
 		if (!bh) {
@@ -3453,7 +3428,6 @@ static int write_dev_supers(struct btrfs_device *device,
 		lock_buffer(bh);
 		bh->b_end_io = btrfs_end_buffer_write_sync;
 		bh->b_private = device;
-		}
 
 		/*
 		 * we fua the first super.  The others we allow
@@ -3471,6 +3445,49 @@ static int write_dev_supers(struct btrfs_device *device,
 	return errors < i ? 0 : -1;
 }
 
+/*
+ * Wait for write completion of superblocks done by write_dev_supers,
+ * @max_mirrors same for write and wait phases.
+ *
+ * Return number of errors when buffer head is not found or not marked up to
+ * date.
+ */
+static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
+{
+	struct buffer_head *bh;
+	int i;
+	int errors = 0;
+	u64 bytenr;
+
+	if (max_mirrors == 0)
+		max_mirrors = BTRFS_SUPER_MIRROR_MAX;
+
+	for (i = 0; i < max_mirrors; i++) {
+		bytenr = btrfs_sb_offset(i);
+		if (bytenr + BTRFS_SUPER_INFO_SIZE >=
+		    device->commit_total_bytes)
+			break;
+
+		bh = __find_get_block(device->bdev, bytenr / 4096,
+				      BTRFS_SUPER_INFO_SIZE);
+		if (!bh) {
+			errors++;
+			continue;
+		}
+		wait_on_buffer(bh);
+		if (!buffer_uptodate(bh))
+			errors++;
+
+		/* drop our reference */
+		brelse(bh);
+
+		/* drop the reference from the writing run */
+		brelse(bh);
+	}
+
+	return errors < i ? 0 : -1;
+}
+
 /*
  * endio for the write_dev_flush, this will wake anyone waiting
  * for the barrier when it is done
@@ -3668,7 +3685,7 @@ int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors)
 		flags = btrfs_super_flags(sb);
 		btrfs_set_super_flags(sb, flags | BTRFS_HEADER_FLAG_WRITTEN);
 
-		ret = write_dev_supers(dev, sb, 0, max_mirrors);
+		ret = write_dev_supers(dev, sb, max_mirrors);
 		if (ret)
 			total_errors++;
 	}
@@ -3691,7 +3708,7 @@ int write_all_supers(struct btrfs_fs_info *fs_info, int max_mirrors)
 		if (!dev->in_fs_metadata || !dev->writeable)
 			continue;
 
-		ret = write_dev_supers(dev, sb, 1, max_mirrors);
+		ret = wait_dev_supers(dev, max_mirrors);
 		if (ret)
 			total_errors++;
 	}