ext4: retry failed direct IO allocations

On a 256M filesystem, doing this in a loop:

xfs_io -F -f -d -c 'pwrite 0 64m' test
rm -f test

eventually leads to ENOSPC. (the xfs_io command does a 64m direct IO write to the file "test")

As with other block allocation callers, it looks like we need to potentially retry the allocations on the initial ENOSPC.

---

index 4abd683..098c466 100644
@@ -3291,6 +3291,7 @@ static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,

	ssize_t ret;
	int orphan = 0;
	size_t count = iov_length(iov, nr_segs);

+ int retries = 0;

	if (rw == WRITE) {
		loff_t final_size = offset + count;
@@ -3313,9 +3314,12 @@ static ssize_t ext4_direct_IO(int rw, struct kiocb *iocb,
		}
	}

+retry:

	ret = blockdev_direct_IO(rw, iocb, inode, inode->i_sb->s_bdev, iov,
				 offset, nr_segs,
				 ext4_get_block, NULL);

+ if (ret == -ENOSPC && ext4_should_retry_alloc(inode->i_sb, &retries))
+ goto retry;

	if (orphan) {
		int err;

Thanks, added to the ext4 patch queue.

- Ted