[U-Boot-Users] fat32 w/o parition table? (a.k.a VBR instead of MBR)

[U-Boot-Users] fat32 w/o parition table? (a.k.a VBR instead of MBR)

[Brad Parker]

After some user complaints about not being able to fatls micro
sd cards which were formatted by Windows XP, I felt compelled to 
make the following change (to u-boot 1.1.6, which I know is ancient,
but looking at the git tree, the latest doesn't handle it either near
as I can tell.

Just curious if anyone has any thoughts.

In the latest code, it seems like checking the partition table first
is dangerous as a VBR might looks like it has a partition table (but it
would be bogus)

Some documents suggest checking the first 3 bytes of the block for the
branch instructions.  The idea being that an MBR with a valid partition
table won't have the branch.  voodoo, I know...

-brad

--- fat.c.orig  2008-05-08 16:18:40.000000000 -0400
+++ fat.c       2008-05-08 12:54:56.000000000 -0400
@@ -52,6 +52,7 @@
 #define DOS_PART_TBL_OFFSET    0x1be
 #define DOS_PART_MAGIC_OFFSET  0x1fe
 #define DOS_FS_TYPE_OFFSET     0x36
+#define DOS_FS_FAT32_TYPE_OFFSET       0x52

 int disk_read (__u32 startblock, __u32 getsize, __u8 * bufptr)
 {
@@ -85,7 +86,9 @@
                return -1;
        }

-       if(!strncmp((char *)&buffer[DOS_FS_TYPE_OFFSET],"FAT",3)) {
+       if(!strncmp((char *)&buffer[DOS_FS_TYPE_OFFSET],"FAT",3) ||
+          !strncmp((char *)&buffer[DOS_FS_FAT32_TYPE_OFFSET],"FAT32",5))
+       {
                /* ok, we assume we are on a PBR only */
                cur_part = 1;
                part_offset=0;


This lets me fatls/fatload from the fat32 file systems created by windows. 

I've done a little FAT hacking, and I think this falls under the
category of "disk with VBR instead of MBR".

-brad

[U-Boot-Users] fat32 w/o parition table? (a.k.a VBR instead of MBR)

[Wolfgang Denk]

Hello,

in message <1998.1210278835@mini> you wrote:
> 
> After some user complaints about not being able to fatls micro
> sd cards which were formatted by Windows XP, I felt compelled to 
> make the following change (to u-boot 1.1.6, which I know is ancient,
> but looking at the git tree, the latest doesn't handle it either near
> as I can tell.
> 
> Just curious if anyone has any thoughts.
> 
> In the latest code, it seems like checking the partition table first
> is dangerous as a VBR might looks like it has a partition table (but it
> would be bogus)
> 
> Some documents suggest checking the first 3 bytes of the block for the
> branch instructions.  The idea being that an MBR with a valid partition
> table won't have the branch.  voodoo, I know...

Strangely enough, this message seems to have received no feedback at
all.

So what do we do about this?

Best regards,

Wolfgang Denk

-- 
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Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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