Re: Beating a dead horse

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Thu, 26 Nov 2015 23:58:17 +0100
    From:        Michael van Elst <mlelstv%serpens.de@localhost>
    Message-ID:  <20151126225816.GB182%serpens.de@localhost>

  | On Thu, Nov 26, 2015 at 06:29:30PM +0700, Robert Elz wrote:
  | 
  | > Just try making a ccd by combining a 512 byte sector drive and a 4K
  | > sector drive, and watch what happens... 
  | 
  | CCD is a very old device that isn't even configured "correctly" and
  | I would be very surprised if it could concat drives of different sector
  | sizes.

It can't.  Or rather, it tries, or permits it anyway, and makes a real mess.

  | After all, what fake geometry should it present to the user?

That at least is easy - it must present the more restricted geom, if any
of the components has 4K sectors (and the others are all <= 4k) then it
must present as a 4K sector size device.   That's simple, and would be
easy to get right, if ccd was really worth continuing with.

  | Yes, CGD is broken. Looks like a simple fix.

The simple fix would be do do what you suggested for lvm, and just
make it appear to have 512 byte sectors, with N * the number of sectors
it really has from the device (for a 4K sector drive, multiply the number
of sectors by 8).   I have no doubt that would kind of function, but again
it would make the cgd "drive" appear to be able to handle 512 byte reads and
writes, which it cannot, because the hardware underneath cannot.

Fixing it to present 4K sectors also looks easy, but isn't.  Doing that
causes a panic somewhere when the cgd is attempting to validate the label
(bsd disklabel) that gets written to it to allow it to be partitioned
(one day it would be nice for cgd to allow GPT labels, and handle them
for validation of the encryption, but that isn't there yet.)

Something in the label handling code is (I think - or guess) translating
units incorrectly, and failing.

Here's the traceback I got ...

vpanic() at vpanic+0x140
snprintf() at snprintf
startlwp() at startlwp
calltrap() at calltrap+0x19
bf_cbc_dec_int() at bf_cbc_dec_int+0x27
cgd_cipher_uio_cbc.isra.0() at cgd_cipher_uio_cbc.isra.0+0x79
cgd_cipher_bf_cbc() at cgd_cipher_bf_cbc+0x8d
cgd_cipher() at cgd_cipher+0x16a
cgdiodone() at cgdiodone+0xaf
biodone2() at biodone2+0x89
dkiodone() at dkiodone+0x84
biodone2() at biodone2+0x89
bdev_strategy() at bdev_strategy+0x5b
spec_strategy() at spec_strategy+0x37
VOP_STRATEGY() at VOP_STRATEGY+0x33
dkstart() at dkstart+0x2b
dkstrategy() at dkstrategy+0xd5
bdev_strategy() at bdev_strategy+0x5b
spec_strategy() at spec_strategy+0x37
VOP_STRATEGY() at VOP_STRATEGY+0x33
cgd_diskstart() at cgd_diskstart+0xb7
dk_start() at dk_start+0x9b
disk_read_sectors() at disk_read_sectors+0x3b
convertdisklabel() at convertdisklabel+0xf0
validate_label() at validate_label+0x14c
readdisklabel() at readdisklabel+0x1c8
dk_getdisklabel() at dk_getdisklabel+0xbf
dk_open() at dk_open+0xf4
cdev_open() at cdev_open+0xb2
spec_open() at spec_open+0x25d
VOP_OPEN() at VOP_OPEN+0x33
vn_open() at vn_open+0x1e3
do_open() at do_open+0x111
do_sys_openat() at do_sys_openat+0x68
sys_open() at sys_open+0x24
syscall() at syscall+0x9c
--- syscall (number 5) ---

kre