Re: [Xen-devel] Xen-Unstable : no eth0 when boot up

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

> ok, now it works. I found you set e100 enabled in defconfig-xen0. So I just
> cloned it again and build it all over again, and it works fine. Thank your
> help.
> btw, I have a question about how xen handle the system calls. Xen has fast
> trap mechanism. But when we commented out the line
>     "HYPERVISOR_set_fast_trap(SYSCALL_VECTOR);"
> in xenolinux-2.4.26/arch/xeno/kernel/traps.c, (talking about 1.2 here)
> xen still performed well. So xen must have something to handle system calls
> from guest OS, right? but we cannot find where it did this. It seems to us
> xen only defined 0-19, not 128 for system calls.

Traps to undefined vectors, or vectors for which the trapper has
insufficient privilege, cause a general protection fault (GPF) with a
particular type of error code. Xen detects that type of error code
and, if the guest OS registered a suitable virtual handler on that
vector, virtualises the GPF as a trap of the appropriate type. If teh
guest OS didn't, then the GPF is virtualised as a GPF in the usual
way. See the "cunning trick" comment in general_protection_fault() in
arch/x86/traps.c. 

 -- Keir



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