Re: kern/57981: ld@virtio confuses F_SEG_MAX negotiation

[Tetsuya Isaki <isaki%pastel-flower.jp@localhost>]

At Sat, 9 Mar 2024 13:27:44 +0000,
Taylor R Campbell wrote:
> Does this affect netbsd-10 or earlier?  Should it be pulled up?

It has been since 2015 (since netbsd-8).
But this will not occur under normal conditions.
So I think it's not necessary to pullup (in a hurry).

Details:
In the previous code, if the maxnsegs read from a virtio device
at line 320 is less than 2, it falls back maxnsegs to larger
value and go.  (By the way, I could not find any description about
it in the virtio spec 1.0, but strictly speaking, it was a protocol
violation, I think...)

When I wrote this PR, I searched which command line option can
specify the SEG_MAX value in QEMU a little.  But I could not find,
so I could not fill 'how-to-repeat' field.
If QEMU has no such option, it will never happen on QEMU.
(It looks to use 254 (=256-2) as the SEG_MAX)

I'm writing a virtio device on my emulator now.  So I could make
it happen intentionally by rewriting the emulator's source code.
But such small SEG_MAX like 1 or 2 is useless for our ld driver.
We usually don't do it, too.
In result, it will only happen on useless devices..

Thanks,
---
Tetsuya Isaki <isaki%pastel-flower.jp@localhost / isaki%NetBSD.org@localhost>