

Persistent storage for a kernel's "dying breath" - rytis
http://lwn.net/Articles/434821/

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Hoff
VMS uses the console boot device drivers (the typical VMS hardware console
program is well past what BIOS offers, and closer to EFI) to write (optionally
compressed, optionally pruned) system crashdump images containing the running
system memory out to a pre-allocated hunk of disk storage.

Use of the console callbacks avoids issues with potential errors or
corruptions within the running system device drivers, while keeping the
exception handler footprint small, and also delegating device dependencies
over to the console drivers.

The last barrage of hardware errors in the system error log buffer (if any)
are specifically and separately captured into a file, too. This ensures that
the error-logging tools can easily capture and log errors that arose in the
run-up to the crash, and without having to know the details of the virtual
memory structures within the crashdump.

~~~
nonane
Windows does something similar, but it uses the swap file as temporary storage
for the crash dump. On next boot, the system checks the swap file for crash
dump signatures. If it finds a crash signature, it creates a minidump out of
it and stores the dump in %SYSTEMROOT%\Minidumps. It also optionally prompts
the user to upload the dump to it's automated analysis servers. I think it
stores a bigger dump in %SYSTEMROOT%\memory.dmp too depending on how the
machine is configured.

~~~
Hoff
That particular Windows behavior is arguably from some of NT's ancestral roots
in the VMS designs.

VMS can also use its pagefile as temporary storage for a system crashdump.

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lsc
oh my, this is useful. Linux has lagged on crash dumps for many years; lacking
a standardized way of dealing with dumps. For years, *BSD has had a much
better and standard (though still imperfect) way of dealing with crash dumps.

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codex
This idea is not new. Macs have had such a device for ages. Among other
things, it stores the speaker volume setting (ever notice Macs don't make the
boot sound at startup if the volume has been muted?) as well as kernel panic
info, which is subsequently relayed to Apple.

~~~
rytis
I'm not too familiar with the matter, but here's a comment from the article:

"Modern macs implement it as an EFI variable. Unsurprisingly, their
implementation is incompatible with the EFI spec's implementation of the
concept."

