Fix USB image corruption issues

Fixes FS#10614
sfdisk and the kernel cannot accurately detect
disk geometry from the disk image file, causing
automatic partition size calculations to fail.
The whole partition table is now calculated
in mkusbimg rather than letting sfdisk do it.

mkusbimg doesn't directly use losetup anymore
either, eliminating some code.

This also fixes issues with needing to make the
partition much larger than necessary, so image
size has been minimized.

Signed-off-by: Simo Leone <simo@archlinux.org>

1 files changed, 26 insertions, 49 deletions

diff --git a/mkusbimg b/mkusbimg
index ba1e5c9..727bb80 100755
--- a/mkusbimg
+++ b/mkusbimg
@@ -16,25 +16,6 @@
 #    You should have received a copy of the GNU General Public License
 #    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
-# next_avail_loop()
-# prints the next available loopback device
-# returns 0 on success
-#         1 on failure
-# XXX: this is only necessary because
-#      the cryptoloop patch for losetup
-#      destroys losetup -f
-next_avail_loop()
-{
-    for i in /dev/loop/*; do
-        echo $(losetup -a|cut -d':' -f1) | grep -q $i
-        if [ $? -eq 1 ]; then
-            echo $i
-            return 0
-        fi
-    done
-    return 1
-}
-
 # usage(exitvalue)
 # outputs a usage message and exits with value
 APPNAME=$(basename "${0}")
@@ -50,52 +31,48 @@ if [ $# -ne 2 ]; then
     usage 1
 fi
 
-IMG="${2}"
+DISKIMG="${2}"
 IMGROOT="${1}"
-LOOPDEV=$(next_avail_loop)
 TMPDIR=$(mktemp -d)
+FSIMG=$(mktemp)
 
-# TODO: there are better ways to do this
-#       than adding 25% to the rootsize
-#  XXX: doesn't seem to boot if we cut it too
-#       close. even if everything fits...
-# IMGSZ >= filesystem overhead + rootsize + 512bytes
-# must hold or there will be insufficient space
+# ext2 overhead's upper bound is 6%
+# empirically tested up to 1GB
 rootsize=$(du -bs ${IMGROOT}|cut -f1)
-IMGSZ=$(( (${rootsize}*5)/4 + 512 ))
-
-# create the image file
-dd if=/dev/zero of="$IMG" bs="$IMGSZ" count=1
+IMGSZ=$(( (${rootsize}*106)/100/512 + 1)) # image size in sectors
 
-# loop mount the disk image
-losetup "$LOOPDEV" "$IMG"
-
-# create a partition table
-# if this looks like voodoo, it's because it is
-echo "63,,,*,"|sfdisk -uS "$LOOPDEV"
+# create the filesystem image file
+dd if=/dev/zero of="$FSIMG" bs=512 count="$IMGSZ"
 
-# loop mount the partition we just made
-# that magic number (offset in bytes to first partition) is more voodoo
-losetup -d "$LOOPDEV"
-losetup -o32256 "$LOOPDEV" "$IMG"
-
-# create a filesystem on our partition
-mke2fs -m 0 "$LOOPDEV"
+# create a filesystem on the image
+mke2fs -m 0 -F "$FSIMG"
 
 # mount the filesystem and copy data
-mount "$LOOPDEV" "$TMPDIR"
+mount -o loop "$FSIMG" "$TMPDIR"
 cp -a "$IMGROOT"/* "$TMPDIR"
 
-# unmount filesystem and loopback
+# unmount filesystem
 umount "$TMPDIR"
-losetup -d "$LOOPDEV"
+
+# add sectors 0-62, then glue together
+dd if=/dev/zero of="$DISKIMG" bs=512 count=63
+cat "$FSIMG" >> "$DISKIMG"
+
+# create a partition table
+# if this looks like voodoo, it's because it is
+sfdisk -uS -f "$DISKIMG" << EOF
+63,$IMGSZ,83,*
+0,0,00
+0,0,00
+0,0,00
+EOF
 
 # install grub on the image
 grub --no-floppy --batch << EOF
-device (hd0) $IMG
+device (hd0) $DISKIMG
 root (hd0,0)
 setup (hd0)
 EOF
 
 # all done :)
-rm -fr "$TMPDIR"
+rm -fr "$TMPDIR" "$FSIMG"