Re: Disklabel question (versus bug)

[Matthew Dillon <dillon@xxxxxxxxxxxxxxxxxxxx>]

:I've used 'dd' extensively while trying to solve my disklabel puzzle.
:
:I just discovered that DragonFly's 'dd', when reading a disklabel
:sector, gives a different result than the 'dd' from FBSD, linux, and
:a raw-disk editor I use on Windows:
:
:# dd if=/dev/ad1s11 iseek=1 count=1 | hd
:1+0 records in
:1+0 records out
:00000000  57 45 56 82 00 00 00 00  44 46 00 00 00 00 00 00  |WEV.....DF......|
:00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
:00000020  00 00 00 00 00 00 00 00  00 02 00 00 3f 00 00 00  |............?...|
:00000030  10 00 00 00 b7 28 00 00  f0 03 00 00 cf 50 a0 00  |.....(.......P..|
:00000040  00 00 00 00 00 00 00 00  10 0e 01 00 00 00 00 00  |................|
:00000050  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
:*
:00000080  00 00 00 00 57 45 56 82  5d 31 08 00 00 20 00 00  |....WEV.]1... ..|
:00000090  00 20 00 00 0e 12 a0 00  00 00 00 00 00 00 00 00  |. ..............|
:000000a0  07 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
:000000b0  00 00 00 00 0e 12 a0 00  00 00 00 00 00 00 00 00  |................|
:000000c0  00 00 00 00 00 00 00 00  00 00 00 00 00 00 00 00  |................|
:*
:512 bytes transferred in 0.008378 secs (61114 bytes/sec)
:
:
:I direct your attention to bytes 908-911, and b08-b11.  These are
:the bytes corresponding to 'p_offset' for partitions 'a' and 'c'
:in the disklabel as defined in disklabel.h:
:
:        struct  partition {             /* the partition table */
:                u_int32_t p_size;       /* number of sectors in partition */
:                u_int32_t p_offset;     /* starting sector */
:
:Now, my problem is that FBSD, linux, and Windows all agree that
:those two 'offset' fields are *wrong*, and are not zeros but
:c0 73 02 09.  This is the correct value for the absolute number
:of sectors from the start of the physical disk to the start of
:ad1s11.

    The disklabel is relative to a slice (ad1s11), NOT the base of
    the raw disk.  The slice has no concept of the rest of the disk.
    This is true of FreeBSD as well.  I have no idea why the numbers
    you are getting would be different.

:I can only conclude that DragonFly's 'dd' is looking at that disk
:sector through eyes that know the difference between a disklabel
:sector and any other sector.  This seems hard to believe, but I
:dunno.
:
:Any thoughts on why DF disagrees with the other three OS's?
:
:Thanks!

					-Matt
					Matthew Dillon 
					<dillon@xxxxxxxxxxxxx>