Joerg Schilling wrote:
>
> Hi all,
>
> from a bugreport that I got ysterday, I must assume that
> the Linux sg driver only checks for kernel memory if more than 32 KB
> is requested for DMA.
Perhaps you could forward me a copy (or translation) of
the bug report. As for your assumption, the sg driver
attempts to use scatter gather for reserved buffer
sizes greater than 32 KB. Kernel memory is "checked"
(i.e. that the allocation was successful) in all cases.
> It seems that newer cdrtools versions that try to use this new
> feature will cause a system panic.
Using scatter gather is a new and painful experience for
some adapters drivers. See the faq on sg's web site:
http://www.torque.net/sg
for some known combinations that cause problems (and
what can/has been done). Most failures I have seen result
in an oops (i.e. system panic).
> If other people notice similar problems, I will need to disable this
> feature until the driver is stable enough for production use.
How is the feature disabled?
> PLease tell me whether you could use cdrecord-1.9 & 1.10alpha
> with ISA SCSI adapters. NOte that only cdda2wav & readcd will
> try to transfer more than 63 KB which seems to be the hard limit
> for ISA Hardware.
By choosing 32 KB as the maximum element size in a scatter
gather list the problems that some ISA adapters have with
the 64 KB limit on a _single_ transfer should be avoided.
This assumes that the adapters safely handle scatter gather
(when their configuration indicates they support it).
SANE 1.0.2 increased its default reserve buffer size from 32 KB
to 128 KB earlier in the year and similar types of problems
began to arise. Nearly all the patches to sg in the last 4
months have been addressing scatter gather problems with
ISA adapters.
Doug Gilbert
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