Hi, That’s a check of btrfs filesystem. see the commit of btrfs-progs: http://git.kernel.org/cgit/linux/kernel/git/kdave/btrfs-progs.git/commit/... btrfs-progs: Add minimum device size check Btrfs has global block reservation, so even mkfs.btrfs can execute without problem, there is still a possibility that the filesystem can't be mounted. For example when mkfs.btrfs on a 8M file on x86_64 platform, kernel will refuse to mount due to ENOSPC, since system block group takes 4M and mixed block group takes 4M, and global block reservation will takes all the 4M from mixed block group, which makes btrfs unable to create uuid tree. This patch will add minimum device size check before actually mkfs. The minimum size calculation uses a simplified one: minimum_size_for_each_dev = 2 * (system block group + global block rsv) and global block rsv = leafsize << 10 From: libguestfs-bounces(a)redhat.com [mailto:libguestfs-bounces@redhat.com] On Behalf Of fu lirong Sent: Tuesday, May 19, 2015 10:01 AM To: libguestfs(a)redhat.com Subject: [Libguestfs] libguestfs error: mkfs_btrfs Hi all : there is a problem on libguestfs-1.29.40 after command :make check libguestfs: error: mkfs_btrfs: /dev/vda1: device /dev/vda1 is too small (must be at least 256 MB) FAIL: test_btrfs_image_0 3/515 test_btrfstune_enable_skinny_metadata_extent_refs_0 libguestfs: error: btrfstune_enable_skinny_metadata_extent_refs: /dev/vda1: btrfstune: invalid option -- 'x' usage: btrfstune [options] device -S value enable/disable seeding FAIL: test_btrfstune_enable_skinny_metadata_extent_refs_0 4/515 test_btrfstune_enable_extended_inode_refs_0 libguestfs: error: btrfstune_enable_extended_inode_refs: /dev/vda1: btrfstune: invalid option -- 'r' usage: btrfstune [options] device -S value enable/disable seeding FAIL: test_btrfstune_enable_extended_inode_refs_0 5/515 test_btrfstune_seeding_0 libguestfs: error: btrfstune_seeding: /dev/vda1: btrfstune: invalid option -- 'f' I found two patch https://www.redhat.com/archives/libguestfs/2012-May/msg00018.htmlvirt-mak... Fix estimation when making btrfs (but there is no virt-make-fs under tools) https://www.redhat.com/archives/libguestfs/2012-April/msg00008.html New API: mkfs-btrfs for creating btrfs filesystems ( It was patched in libguestfs-1.29.40) It seems stupid, but I can't find the answer, I am sorry