> It always chokes on fp->fsisig4.
Well, that's what you get from reading 512 bytes and casting the buffer
to a 1024 byte struct.
The following diff ought to solve this.
Index: msdos/msdosfs_vfsops.c
===================================================================
RCS file: /OpenBSD/src/usr.sbin/makefs/msdos/msdosfs_vfsops.c,v
retrieving revision 1.13
diff -u -p -r1.13 msdosfs_vfsops.c
--- msdos/msdosfs_vfsops.c 6 Oct 2021 00:40:41 -0000 1.13
+++ msdos/msdosfs_vfsops.c 1 Dec 2023 06:52:40 -0000
@@ -278,7 +278,8 @@ msdosfs_mount(struct mkfsvnode *devvp, i
DPRINTF(("%s(bread %lu)\n", __func__,
(unsigned long)de_bn2kb(pmp, pmp->pm_fsinfo)));
if ((error = bread(devvp, de_bn2kb(pmp, pmp->pm_fsinfo),
- pmp->pm_BytesPerSec, 0, &bp)) != 0)
+ roundup(sizeof(struct fsinfo), pmp->pm_BytesPerSec),
+ 0, &bp)) != 0)
goto error_exit;
fp = (struct fsinfo *)bp->b_data;
if (!memcmp(fp->fsisig1, "RRaA", 4)
