Hello,
I try to fix a bug I have found with parted-2.3 while using a special
USB key (Model: disk2go PURE II) that expose two storage devices: a
small 5MB device and a regular 2GB device. Here are the 5MB one viewed
by using fdisk:
fdisk -l /dev/sdb
Disk /dev/sdb: 5 MB, 5242880 bytes
256 heads, 32 sectors/track, 1 cylinders
Units = cylinders of 8192 * 512 = 4194304 bytes
Disk identifier: 0x00000000
Device Boot Start End Blocks Id System
/dev/sdb1 1 1 4080 6 FAT16
The first 5MB device have, acoording to parted-2.3, a cylinder size
(16065) not smaller than the device length (10240), causing the
PedGeometry start_geom of the function _primary_constraint() (file
libparted/labels/dos.c) to stay uninitialized. I suspect that the
condition "cylinder_size < dev->length" have bee introduced for the
memory-mapped test as explained into the comment above the condition.
Unfortunately, it seem that the true real world contain at least a type
of USB key sold with a storage device that go wrong with this condition.
I don't know the parted code enough to propose better patch than the
attached one that remove the condition. Obviously it will cause the
memory-mapped test to fail. With the proposed patch, parted-2.3 work as
expected when compiled without optimization:
j...@point:~/parted-testing/build-O0$ parted/parted /dev/sdb print
WARNING: You are not superuser. Watch out for permissions.
Error: Can't have the end before the start! (start sector=16065
length=-5825)
Model: disk2go PURE II (scsi)
Disk /dev/sdb: 5243kB
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 5120B 5243kB 5238kB primary
The bug was first reported to Debian:
http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=602568 but this is
reproductible without any Debian patch.
Warning: as this debug screen capture show, this bug occur only if
parted is compiled without any optimization:
http://bugs.debian.org/cgi-bin/bugreport.cgi?msg=71;filename=Capture-parted-2.3.png;att=1;bug=602568
Regards,
Jean-Christian de Rivaz
--- libparted/labels/dos.c.orig 2010-05-25 15:42:21.000000000 +0200
+++ libparted/labels/dos.c 2010-11-08 14:56:33.000000000 +0100
@@ -1638,13 +1638,14 @@
dev->length - min_geom->end))
return NULL;
} else {
+ /* TO BE FIXED as testing if (cylinder_size < dev->length)
+ is not enough. See Debian bug #602568. Original comment:
/* Do not assume that length is larger than 1 cylinder's
worth of sectors. This is useful when testing with
a memory-mapped "disk" (a la scsi_debug) that is say,
2048 sectors long. */
- if (cylinder_size < dev->length
- && !ped_geometry_init (&start_geom, dev, cylinder_size,
- dev->length - cylinder_size))
+ if (!ped_geometry_init (&start_geom, dev, cylinder_size,
+ dev->length - cylinder_size))
return NULL;
if (!ped_geometry_init (&end_geom, dev, 0, dev->length))
return NULL;
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