Distinguish between first LBA sector and partition

An insufficient check leads to an invalid free space output, as seen here:

$ dd if=/dev/zero of=cfdisk.iso bs=1M count=1
$ losetup -f cfdisk.iso
$ echo w | fdisk /dev/loop0
$ echo '1,1' | sfdisk /dev/loop0 --append
$ echo '3,' | sfdisk /dev/loop0 --append
$ sfdisk --list-free /dev/loop0
Start End Sectors Size
    1   2       2   1K
$ _

In this case, libfdisk fails to notice that it tries to calculate space between two partitions, not between start of disk and first partition. Currently, the code tries to achieve that by checking the address of the last "partition", which is the first_lba block. Now if the first partition is merely 1 block in size, the "last" address is still equal to the first_lba block, which renders the check in libfdisk for the next partition invalid.

I chose to use "nparts == 0" for this check, because the partitions are properly sorted before iterating over them.

---
 libfdisk/src/table.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

index bf30d1b..f975168 100644
@@ -617,9 +617,9 @@ int fdisk_get_freespaces(struct fdisk_context *cxt, struct fdisk_table **tb)
 		 * aligned, the exception is space before the first partition where
 		 * we assume that cxt->first_lba is aligned. */
 		if (last + grain < pa->start
-		    || (last < pa->start && last == cxt->first_lba)) {
+		    || (last < pa->start && nparts == 0)) {
 			rc = table_add_freespace(cxt, *tb,
-				last + (last > cxt->first_lba ? 1 : 0),
+				last + (nparts == 0 ? 0 : 1),
 				pa->start - 1, NULL);
 		}
 		/* add gaps between logical partitions */

2.9.3

Applied, thanks.

 Karel Zak  <[email protected]>
 http://karelzak.blogspot.com