[PATCH v2 1/3] btrfs-progs: error if device for mkfs is too small

[Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>]

Eric pointed out that mkfs abort if specified volume is too small:

  # truncate --size=2m testfile
  # ./mkfs.btrfs testfile
   :
  SMALL VOLUME: forcing mixed metadata/data groups
  mkfs.btrfs: volumes.c:852: btrfs_alloc_chunk: Assertion `!(ret)' failed.
  Aborted (core dumped)

As the first step to fix problems around there, let mkfs to report
error if the size of target volume is less than the size of the first
system block group, BTRFS_MKFS_SYSTEM_GROUP_SIZE (= 4MB).

Reported-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Hidetoshi Seto <seto.hidetoshi@jp.fujitsu.com>
---
 mkfs.c |    6 ++++++
 1 files changed, 6 insertions(+), 0 deletions(-)

diff --git a/mkfs.c b/mkfs.c
index b412b7e..a98fe54 100644
--- a/mkfs.c
+++ b/mkfs.c
@@ -1422,6 +1422,12 @@ int main(int ac, char **av)
 		}
 	}
 
+	/* To create the first block group and chunk 0 in make_btrfs */
+	if (dev_block_count < BTRFS_MKFS_SYSTEM_GROUP_SIZE) {
+		fprintf(stderr, "device is too small to make filesystem\n");
+		exit(1);
+	}
+
 	blocks[0] = BTRFS_SUPER_INFO_OFFSET;
 	for (i = 1; i < 7; i++) {
 		blocks[i] = BTRFS_SUPER_INFO_OFFSET + 1024 * 1024 +
-- 
1.7.1