From: Robin Dong <redacted>

Using mkfs.btrfs like:

        mkfs.btrfs -b 1048576 /dev/sda

will report error:

	mkfs.btrfs: volumes.c:796: btrfs_alloc_chunk: Assertion `!(ret)' failed.
	Aborted

because the length of dev_extent is 4MB.

But if we use mkfs.btrfs with 8MB total bytes, the newly mounted btrfs filesystem
would not contain even one empty file. So 12MB will be good min-value for block_count.

Signed-off-by: Robin Dong <redacted>
---
 mkfs.c |    6 +++++-
 1 files changed, 5 insertions(+), 1 deletions(-)

diff --git a/mkfs.c b/mkfs.c
index 8420482..496faa8 100644
--- a/mkfs.c
+++ b/mkfs.c

@@ -1345,7 +1345,11 @@ int main(int ac, char **av)
 				&dev_block_count, &mixed, nodiscard);
 		if (block_count == 0)
 			block_count = dev_block_count;
-		else if (block_count > dev_block_count) {
+		else if (block_count < 3 * BTRFS_MKFS_SYSTEM_GROUP_SIZE) {
+			fprintf(stderr, "Illegal total number of bytes %u\n",
+					block_count);
+			exit(1);
+		} else if (block_count > dev_block_count) {
 			fprintf(stderr, "%s is smaller than requested size\n", file);
 			exit(1);
 		}

-- 
1.7.3.2