Chris,

I've examined this bug by putting copious amounts of debug in squashfs
and building a debugged version of the live CD. I've then tracking this
through the scsi subsystem down to the ata driver level. I believe the
bug is an underlying ata driver issue which may not be easily resolved
in 2.6.24.

Basically, the squashfs filesystem is loop back mounted from the file
casper/filesystem.squashfs on the live CD.  When the system goes into
suspend/cycle, the ata driver is not suspended/resumed correctly causing
I/O reads in the block layer to fail which ultimately causes squashfs to
produce the error messages.

Originally I thought this looked like just an 64 bit kernel issue, but
one can reproduce this bug with the 32 it version as well by selection
one of the consoles, suspending and resuming and immediately the machine
resumes type a command that is not cached in memory. This forces
squashfs to read some blocks off the CD (from the loop back mounted
filesytem squashfs image) and the ata driver fails with an I/O error -
mainly because it is in a unknown state because suspend may not be
implemented for the ata controller.

One can show this is not a squashfs bug by inserting any CD-ROM and
running dd on an installed Hardy system:

sudo dd if=/dev/scd0 of=/dev/zero

and doing a suspend resume cycle.

The mystery is why this succeeds with non CD-ROM drives such as a hard
disk over a suspend/resume cycle, e.g.:

sudo dd if=/dev/sda of=/dev/zero

I conclude that the crux of the matter is the implementation of suspend
resume for your ata driver. Looking at
http://ata.wiki.kernel.org/index.php/Software_status it states:

"System suspend/resume (suspend-to-RAM, suspend-to-disk) is currently
supported for ata_piix, ahci, sata_sil and sata_sil24 drivers.

ACPI support is also needed in certain situations, to ensure that Linux
properly initializes the device on boot, and after resume. A patch from
Intel is available in -mm and libata-dev.git for this. "

I shall see if the patch is applicable and resolved the issue.

Colin

-- 
[hardy beta] [amd64] squashfs errors on resume from desktop cd
https://bugs.launchpad.net/bugs/203984
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