Device helper cleanups

index c95f018d4a1e..39deba4e88e3 100644
@@ -152,7 +152,15 @@ struct list_head *btrfs_get_fs_uuids(void)
 	return &fs_uuids;
 }
 
-static struct btrfs_fs_devices *__alloc_fs_devices(void)
+/*
+ * alloc_fs_devices - allocate struct btrfs_fs_devices
+ * @fsid:	if not NULL, copy the uuid to fs_devices::fsid
+ *
+ * Return a pointer to a new struct btrfs_fs_devices on success, or ERR_PTR().
+ * The returned struct is not linked onto any lists and can be destroyed with
+ * kfree() right away.
+ */
+static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid)
 {
 	struct btrfs_fs_devices *fs_devs;
 

@@ -166,31 +174,8 @@ static struct btrfs_fs_devices *__alloc_fs_devices(void)
 	INIT_LIST_HEAD(&fs_devs->resized_devices);
 	INIT_LIST_HEAD(&fs_devs->alloc_list);
 	INIT_LIST_HEAD(&fs_devs->list);
-
-	return fs_devs;
-}
-
-/**
- * alloc_fs_devices - allocate struct btrfs_fs_devices
- * @fsid:	a pointer to UUID for this FS.  If NULL a new UUID is
- *		generated.
- *
- * Return: a pointer to a new &struct btrfs_fs_devices on success;
- * ERR_PTR() on error.  Returned struct is not linked onto any lists and
- * can be destroyed with kfree() right away.
- */
-static struct btrfs_fs_devices *alloc_fs_devices(const u8 *fsid)
-{
-	struct btrfs_fs_devices *fs_devs;
-
-	fs_devs = __alloc_fs_devices();
-	if (IS_ERR(fs_devs))
-		return fs_devs;
-
 	if (fsid)
 		memcpy(fs_devs->fsid, fsid, BTRFS_FSID_SIZE);
-	else
-		generate_random_uuid(fs_devs->fsid);
 
 	return fs_devs;
 }

@@ -2202,7 +2187,7 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
 	if (!fs_devices->seeding)
 		return -EINVAL;
 
-	seed_devices = __alloc_fs_devices();
+	seed_devices = alloc_fs_devices(NULL);
 	if (IS_ERR(seed_devices))
 		return PTR_ERR(seed_devices);
 

@@ -6568,6 +6553,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
 	int ret;
 
 	BUG_ON(!mutex_is_locked(&uuid_mutex));
+	ASSERT(fsid);
 
 	fs_devices = fs_info->fs_devices->seed;
 	while (fs_devices) {

index 39deba4e88e3..c3eafc8367d5 100644
@@ -254,9 +254,17 @@ static struct btrfs_device *__alloc_device(void)
 	return dev;
 }
 
-static noinline struct btrfs_device *__find_device(struct list_head *head,
-						   u64 devid, u8 *uuid)
+/*
+ * Find a device specified by @devid or @uuid in the list of @fs_devices, or
+ * return NULL.
+ *
+ * If devid and uuid are both specified, the match must be exact, otherwise
+ * only devid is used.
+ */
+static struct btrfs_device *find_device(struct btrfs_fs_devices *fs_devices,
+		u64 devid, const u8 *uuid)
 {
+	struct list_head *head = &fs_devices->devices;
 	struct btrfs_device *dev;
 
 	list_for_each_entry(dev, head, dev_list) {

@@ -621,8 +629,8 @@ static noinline int device_list_add(const char *path,
 
 		device = NULL;
 	} else {
-		device = __find_device(&fs_devices->devices, devid,
-				       disk_super->dev_item.uuid);
+		device = find_device(fs_devices, devid,
+				disk_super->dev_item.uuid);
 	}
 
 	if (!device) {

@@ -6280,8 +6288,7 @@ struct btrfs_device *btrfs_find_device(struct btrfs_fs_info *fs_info, u64 devid,
 	while (cur_devices) {
 		if (!fsid ||
 		    !memcmp(cur_devices->fsid, fsid, BTRFS_UUID_SIZE)) {
-			device = __find_device(&cur_devices->devices,
-					       devid, uuid);
+			device = find_device(cur_devices, devid, uuid);
 			if (device)
 				return device;
 		}

index 075beedb4352..df4772918ebb 100644
@@ -3378,19 +3378,17 @@ 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;

@@ -3408,57 +3406,33 @@ 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++;
+		btrfs_set_super_bytenr(sb, bytenr);
 
-			/* drop our reference */
-			brelse(bh);
+		crc = ~(u32)0;
+		crc = btrfs_csum_data((const char *)sb + BTRFS_CSUM_SIZE, crc,
+				      BTRFS_SUPER_INFO_SIZE - BTRFS_CSUM_SIZE);
+		btrfs_csum_final(crc, sb->csum);
 
-			/* drop the reference from the wait == 0 run */
-			brelse(bh);
+		/* One reference for us, and we leave it for the caller */
+		bh = __getblk(device->bdev, bytenr / 4096,
+			      BTRFS_SUPER_INFO_SIZE);
+		if (!bh) {
+			btrfs_err(device->fs_info,
+			    "couldn't get super buffer head for bytenr %llu",
+			    bytenr);
+			errors++;
 			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);
-			btrfs_csum_final(crc, sb->csum);
-
-			/*
-			 * one reference for us, and we leave it for the
-			 * caller
-			 */
-			bh = __getblk(device->bdev, bytenr / 4096,
-				      BTRFS_SUPER_INFO_SIZE);
-			if (!bh) {
-				btrfs_err(device->fs_info,
-				    "couldn't get super buffer head for bytenr %llu",
-				    bytenr);
-				errors++;
-				continue;
-			}
+		}
 
-			memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
+		memcpy(bh->b_data, sb, BTRFS_SUPER_INFO_SIZE);
 
-			/* one reference for submit_bh */
-			get_bh(bh);
+		/* one reference for submit_bh */
+		get_bh(bh);
 
-			set_buffer_uptodate(bh);
-			lock_buffer(bh);
-			bh->b_end_io = btrfs_end_buffer_write_sync;
-			bh->b_private = device;
-		}
+		set_buffer_uptodate(bh);
+		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

@@ -3477,6 +3451,49 @@ static int write_dev_supers(struct btrfs_device *device,
 }
 
 /*
+ * 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
  */

@@ -3737,7 +3754,7 @@ 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++;
 	}

@@ -3760,7 +3777,7 @@ 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++;
 	}

index e3b1d08dd03c..060893141fe9 100644
@@ -795,12 +795,12 @@ static int btrfsic_process_superblock_dev_mirror(
 	dev_bytenr = btrfs_sb_offset(superblock_mirror_num);
 	if (dev_bytenr + BTRFS_SUPER_INFO_SIZE > device->commit_total_bytes)
 		return -1;
-	bh = __bread(superblock_bdev, dev_bytenr / 4096,
+	bh = __bread(superblock_bdev, dev_bytenr / BTRFS_BDEV_BLOCKSIZE,
 		     BTRFS_SUPER_INFO_SIZE);
 	if (NULL == bh)
 		return -1;
 	super_tmp = (struct btrfs_super_block *)
-	    (bh->b_data + (dev_bytenr & 4095));
+	    (bh->b_data + (dev_bytenr & (BTRFS_BDEV_BLOCKSIZE - 1)));
 
 	if (btrfs_super_bytenr(super_tmp) != dev_bytenr ||
 	    btrfs_super_magic(super_tmp) != BTRFS_MAGIC ||

@@ -2758,7 +2758,7 @@ int btrfsic_submit_bh(int op, int op_flags, struct buffer_head *bh)
 	    (op == REQ_OP_WRITE) && bh->b_size > 0) {
 		u64 dev_bytenr;
 
-		dev_bytenr = 4096 * bh->b_blocknr;
+		dev_bytenr = BTRFS_BDEV_BLOCKSIZE * bh->b_blocknr;
 		if (dev_state->state->print_mask &
 		    BTRFSIC_PRINT_MASK_SUBMIT_BIO_BH)
 			pr_info("submit_bh(op=0x%x,0x%x, blocknr=%llu (bytenr %llu), size=%zu, data=%p, bdev=%p)\n",

index df4772918ebb..aa94b6578c36 100644
@@ -2694,8 +2694,8 @@ int open_ctree(struct super_block *sb,
 	btrfs_init_balance(fs_info);
 	btrfs_init_async_reclaim_work(&fs_info->async_reclaim_work);
 
-	sb->s_blocksize = 4096;
-	sb->s_blocksize_bits = blksize_bits(4096);
+	sb->s_blocksize = BTRFS_BDEV_BLOCKSIZE;
+	sb->s_blocksize_bits = blksize_bits(BTRFS_BDEV_BLOCKSIZE);
 
 	btrfs_init_btree_inode(fs_info);
 

@@ -3321,7 +3321,7 @@ int btrfs_read_dev_one_super(struct block_device *bdev, int copy_num,
 	if (bytenr + BTRFS_SUPER_INFO_SIZE >= i_size_read(bdev->bd_inode))
 		return -EINVAL;
 
-	bh = __bread(bdev, bytenr / 4096, BTRFS_SUPER_INFO_SIZE);
+	bh = __bread(bdev, bytenr / BTRFS_BDEV_BLOCKSIZE, BTRFS_SUPER_INFO_SIZE);
 	/*
 	 * If we fail to read from the underlying devices, as of now
 	 * the best option we have is to mark it EIO.

@@ -3414,7 +3414,7 @@ static int write_dev_supers(struct btrfs_device *device,
 		btrfs_csum_final(crc, sb->csum);
 
 		/* One reference for us, and we leave it for the caller */
-		bh = __getblk(device->bdev, bytenr / 4096,
+		bh = __getblk(device->bdev, bytenr / BTRFS_BDEV_BLOCKSIZE,
 			      BTRFS_SUPER_INFO_SIZE);
 		if (!bh) {
 			btrfs_err(device->fs_info,

@@ -3473,7 +3473,8 @@ static int wait_dev_supers(struct btrfs_device *device, int max_mirrors)
 		    device->commit_total_bytes)
 			break;
 
-		bh = __find_get_block(device->bdev, bytenr / 4096,
+		bh = __find_get_block(device->bdev,
+				      bytenr / BTRFS_BDEV_BLOCKSIZE,
 				      BTRFS_SUPER_INFO_SIZE);
 		if (!bh) {
 			errors++;

index 4654d129aa76..995d0aa0abe4 100644
@@ -25,6 +25,14 @@
 #define BTRFS_SUPER_MIRROR_MAX	 3
 #define BTRFS_SUPER_MIRROR_SHIFT 12
 
+/*
+ * Fixed blocksize for all devices, applies to specific ways of reading
+ * metadata like superblock. Must meet the set_blocksize requirements.
+ *
+ * Do not change.
+ */
+#define BTRFS_BDEV_BLOCKSIZE	(4096)
+
 enum btrfs_wq_endio_type {
 	BTRFS_WQ_ENDIO_DATA = 0,
 	BTRFS_WQ_ENDIO_METADATA = 1,

index c3eafc8367d5..327b05c14592 100644
@@ -303,7 +303,7 @@ btrfs_get_bdev_and_sb(const char *device_path, fmode_t flags, void *holder,
 
 	if (flush)
 		filemap_write_and_wait((*bdev)->bd_inode->i_mapping);
-	ret = set_blocksize(*bdev, 4096);
+	ret = set_blocksize(*bdev, BTRFS_BDEV_BLOCKSIZE);
 	if (ret) {
 		blkdev_put(*bdev, flags);
 		goto error;

@@ -2400,7 +2400,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *device_path
 	device->is_tgtdev_for_dev_replace = 0;
 	device->mode = FMODE_EXCL;
 	device->dev_stats_valid = 1;
-	set_blocksize(device->bdev, 4096);
+	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
 
 	if (seeding_dev) {
 		sb->s_flags &= ~MS_RDONLY;

@@ -2605,7 +2605,7 @@ int btrfs_init_dev_replace_tgtdev(struct btrfs_fs_info *fs_info,
 	device->is_tgtdev_for_dev_replace = 1;
 	device->mode = FMODE_EXCL;
 	device->dev_stats_valid = 1;
-	set_blocksize(device->bdev, 4096);
+	set_blocksize(device->bdev, BTRFS_BDEV_BLOCKSIZE);
 	device->fs_devices = fs_info->fs_devices;
 	list_add(&device->dev_list, &fs_info->fs_devices->devices);
 	fs_info->fs_devices->num_devices++;