Hi Lawrence,
thanks for your bug report and patch.
On Wed, Sep 30, 2009 at 03:15:41PM +0200, Lawrence Rust wrote:
> function. A very important feature of these disks is the boot signature -
> bytes 0x55, 0xaa at the end of the 1st sector which indicate to the BIOS that
Ah.. yes, I know. I fixed exactly the same problem in libvolume_id
few years ago :-) Unfortunately, this 0x55 0xaa check wasn't ported
to libblkid.
> To fix this I wrote this small patch to check for the 0x55, 0xaa bytes at the
> end of the sector:
You didn't test the patch, right? :-)
> + /* Old floppies have a valid MBR signature */
> + if (ms->ms_pmagic[0] != 0x55 || ms->ms_pmagic[1] != 0xAA)
> + return 1;
there was a wrong comment in msdos_super_block, the ms_pmagic is at
0xef offset. The MBR signature is at 0x1ef.
Fixed, see the patch below.
Karel
diff --git a/shlibs/blkid/src/superblocks/vfat.c b/shlibs/blkid/src/superblocks/vfat.c
index 9c20ebd..633e009 100644
--- a/shlibs/blkid/src/superblocks/vfat.c
+++ b/shlibs/blkid/src/superblocks/vfat.c
@@ -46,7 +46,7 @@ struct vfat_super_block {
/* 47*/ unsigned char vs_label[11];
/* 52*/ unsigned char vs_magic[8];
/* 5a*/ unsigned char vs_dummy2[164];
-/*1fe*/ unsigned char vs_pmagic[2];
+/* fe*/ unsigned char vs_pmagic[2];
};
/* Yucky misaligned values */
@@ -58,19 +58,21 @@ struct msdos_super_block {
/* 0e*/ uint16_t ms_reserved;
/* 10*/ uint8_t ms_fats;
/* 11*/ unsigned char ms_dir_entries[2];
-/* 13*/ unsigned char ms_sectors[2];
+/* 13*/ unsigned char ms_sectors[2]; /* =0 iff V3 or later */
/* 15*/ unsigned char ms_media;
-/* 16*/ uint16_t ms_fat_length;
+/* 16*/ uint16_t ms_fat_length; /* Sectors per FAT */
/* 18*/ uint16_t ms_secs_track;
/* 1a*/ uint16_t ms_heads;
/* 1c*/ uint32_t ms_hidden;
-/* 20*/ uint32_t ms_total_sect;
-/* 24*/ unsigned char ms_unknown[3];
+/* V3 BPB */
+/* 20*/ uint32_t ms_total_sect; /* iff ms_sectors == 0 */
+/* V4 BPB */
+/* 24*/ unsigned char ms_unknown[3]; /* Phys drive no., resvd, V4 sig (0x29) */
/* 27*/ unsigned char ms_serno[4];
/* 2b*/ unsigned char ms_label[11];
/* 36*/ unsigned char ms_magic[8];
-/* 3d*/ unsigned char ms_dummy2[192];
-/*1fe*/ unsigned char ms_pmagic[2];
+/* 3e*/ unsigned char ms_dummy2[192];
+/* fe*/ unsigned char ms_pmagic[2];
};
struct vfat_dir_entry {
@@ -138,6 +140,15 @@ static unsigned char *search_fat_label(struct vfat_dir_entry *dir, int count)
static int probe_fat_nomagic(blkid_probe pr, const struct blkid_idmag *mag)
{
struct msdos_super_block *ms;
+ unsigned char *buf;
+
+ buf = blkid_probe_get_sector(pr, 0);
+ if (!buf)
+ return -1;
+
+ /* Old floppies have a valid MBR signature */
+ if (buf[510] != 0x55 || buf[511] != 0xAA)
+ return 1;
ms = blkid_probe_get_sb(pr, mag, struct msdos_super_block);
if (!ms)
--
1.6.2.5
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