From: "Richard W.M. Jones" <rjones(a)redhat.com&gt; If you use virt-make-fs to create a partitionless FAT-formatted disk image then currently you will get an error: $ virt-make-fs --type=fat . /tmp/test.img 'mkfs' (create filesystem) operation failed. Instead of 'fat', try 'vfat' (long filenames) or 'msdos' (short filenames). mkfs: fat: /dev/sda: mkfs.fat: Device partition expected, not making filesystem on entire device '/dev/sda' (use -I to override) at /usr/bin/virt-make-fs line 508, <PIPE> line 1. ...propagated at /usr/bin/virt-make-fs line 518, <PIPE> line 1. With this patch, the error goes away and partitionless disks can be created. --- daemon/mkfs.c | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/daemon/mkfs.c b/daemon/mkfs.c index e753d9a..ee0e9d1 100644 --- a/daemon/mkfs.c +++ b/daemon/mkfs.c @@ -96,6 +96,11 @@ do_mkfs (const char *fstype, const char *device, int blocksize, ADD_ARG (argv, i, "-O"); } + /* Force mkfs.fat to create a whole disk filesystem (RHBZ#1039995). */ + if (STREQ (fstype, "fat") || STREQ (fstype, "vfat") || + STREQ (fstype, "msdos")) + ADD_ARG (argv, i, "-I"); + /* Process blocksize parameter if set. */ if (optargs_bitmask & GUESTFS_MKFS_BLOCKSIZE_BITMASK) { if (blocksize <= 0 || !is_power_of_2 (blocksize)) { -- 1.8.3.1