libparted and hidden FAT partitions

[Thomas Viehmann]

Hi,

a bug has been reported to the Debian BTS[1] about breaking hidden FAT
partitions that seems relate to libparted. Ben Hutchins prepared a patch
to have parted preserve hidden fat partitions[2], but it is unclear
whether that behaviour is ideal in all situations, so we (Otavio asked
me to forward this because he is busy enough with his other Debian work
to delegate forwarding this) would appreciate if you could offer some
comment on the problem and/or the proposed solution.

Kind regards

T.

1. http://bugs.debian.org/491797
2. in the bug log[1], also attached for your convenience
-- 
Thomas Viehmann, http://thomas.viehmann.net/

Here's a patch for this.  I constructed a table with two FAT partitions
on a memory card, hid one partition by changing its type code, and then
verified that fatresize would destroy the hidden partition but would
leave it intact once I applied this patch to libparted.

I am not going to NMU because I'm unsure whether it's generally a good
idea to leave hidden partitions untouched.  If it is, please apply this.

Ben.

#! /bin/sh /usr/share/dpatch/dpatch-run
## preserve-hidden-parts.dpatch by Ben Hutchings <address@hidden>
##
## All lines beginning with `## DP:' are a description of the patch.
## DP: This is an attempt to fix bug #491797.  It changes the partition
## DP: rewriting code to set only the type code in entries for empty or
## DP: hidden partitions, so that hidden partitions should be preserved
## DP: so long as we don't resize another partition over them.

@DPATCH@
diff -urNad parted-1.8.8.git.2008.03.24~/libparted/labels/dos.c 
parted-1.8.8.git.2008.03.24/libparted/labels/dos.c
--- parted-1.8.8.git.2008.03.24~/libparted/labels/dos.c 2008-10-05 
22:24:07.000000000 +0100
+++ parted-1.8.8.git.2008.03.24/libparted/labels/dos.c  2008-10-05 
22:43:43.000000000 +0100
@@ -1148,13 +1148,17 @@
        if (!table.mbr_signature)
                table.mbr_signature = generate_random_id();
 
-       memset (table.partitions, 0, sizeof (DosRawPartition) * 4);
-       table.magic = PED_CPU_TO_LE16 (MSDOS_MAGIC);
+       if (table.magic != PED_CPU_TO_LE16 (MSDOS_MAGIC)) {
+               memset (table.partitions, 0, sizeof (DosRawPartition) * 4);
+               table.magic = PED_CPU_TO_LE16 (MSDOS_MAGIC);
+       }
 
        for (i=1; i<=4; i++) {
                part = ped_disk_get_partition (disk, i);
-               if (!part)
+               if (!part) {
+                       table.partitions [i - 1].type = PARTITION_EMPTY;
                        continue;
+               }
 
                if (!fill_raw_part (&table.partitions [i - 1], part, 0))
                        return 0;
--- END ---