Re: [Qemu-devel] VirtIO 9p mount_tag (bogus?) limit of 32 bytes

[Paul Brook]

> i see an error message has been added, which is great (i killed a
> couple hours of $%!@ until i noticed the truncated length was *exactly
> 32* bytes; silent truncation), but it would really be great if this
> restriction could be lifted, or at least mitigated by expanding the
> field some.
> 
> is config space that precious?  

Yes.

> what constrains it (personal curiosity :-)?

Virtio PCI devices map the config space directly onto an ISA IO port range, 
along with the virtio control structure.  On most systems (in particular 
anything PC based) this is a 16-bit address space.  i.e. you have 
substantually less than 64k of virtio config space for the whole machine, and 
potentially only a couple of kbytes for a given PCI bus.

Paul