+/*
+ * endio for the write_dev_flush, this will wake anyone waiting
+ * for the barrier when it is done
+ */
+static void btrfs_end_empty_barrier(struct bio *bio, int err)
+{
+ if (err) {
+ if (err == -EOPNOTSUPP)
+ set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
+ clear_bit(BIO_UPTODATE, &bio->bi_flags);
+ }
+ if (bio->bi_private)
+ complete(bio->bi_private);
+ bio_put(bio);
+}
+
+/*
+ * trigger flushes for one the devices. If you pass wait == 0, the flushes are
+ * sent down. With wait == 1, it waits for the previous flush.
+ *
+ * any device where the flush fails with eopnotsupp are flagged as not-barrier
+ * capable
+ */
+static int write_dev_flush(struct btrfs_device *device, int wait)
+{
+ struct bio *bio;
+ int ret = 0;
+
+ if (device->nobarriers)
+ return 0;
+
+ if (wait) {
+ bio = device->flush_bio;
+ if (!bio)
+ return 0;
+
+ wait_for_completion(&device->flush_wait);
+
+ if (bio_flagged(bio, BIO_EOPNOTSUPP)) {
+ printk("btrfs: disabling barriers on dev %s\n",
+ device->name);
+ device->nobarriers = 1;
+ }
+ if (!bio_flagged(bio, BIO_UPTODATE)) {
+ ret = -EIO;
+ }
+
+ /* drop the reference from the wait == 0 run */
+ bio_put(bio);
+ device->flush_bio = NULL;
+
+ return ret;
+ }
+
+ /*
+ * one reference for us, and we leave it for the
+ * caller
+ */
+ device->flush_bio = NULL;;
+ bio = bio_alloc(GFP_NOFS, 0);
+ if (!bio)
+ return -ENOMEM;
+
+ bio->bi_end_io = btrfs_end_empty_barrier;
+ bio->bi_bdev = device->bdev;
+ init_completion(&device->flush_wait);
+ bio->bi_private = &device->flush_wait;
+ device->flush_bio = bio;
+
+ bio_get(bio);
+ submit_bio(WRITE_FLUSH, bio);
+
+ return 0;
+}
+
+/*
+ * send an empty flush down to each device in parallel,
+ * then wait for them
+ */
+static int barrier_all_devices(struct btrfs_fs_info *info)
+{
+ struct list_head *head;
+ struct btrfs_device *dev;
+ int errors = 0;
+ int ret;
+
+ /* send down all the barriers */
+ head = &info->fs_devices->devices;
+ list_for_each_entry_rcu(dev, head, dev_list) {
+ if (dev->missing)
+ continue;
+ if (!dev->bdev) {
+ errors++;
+ continue;
+ }
+ if (!dev->in_fs_metadata || !dev->writeable)
+ continue;
+
+ ret = write_dev_flush(dev, 0);
+ if (ret)
+ errors++;
+ }
+
+ /* wait for all the barriers */
+ list_for_each_entry_rcu(dev, head, dev_list) {
+ if (dev->missing)
+ continue;
+ if (!dev->bdev) {
+ errors++;
+ continue;
+ }
+ if (!dev->in_fs_metadata || !dev->writeable)
+ continue;
+
+ ret = write_dev_flush(dev, 1);
+ if (ret)
+ errors++;
+ }
+ if (errors)
+ return -EIO;
+ return 0;
+}
+