Re: [Qemu-devel] [RFC] linux-user (mostly syscall.c)

[Thiemo Seufer <ths@networkno.de>]

Thayne Harbaugh wrote:
> There are several things that I'd like to see addressed in linux-user.
> Some of these are to fix bugs, some are to make qemu linux-user more
> like the Linux kernel, some are to make the internal qemu interfaces
> more consistent.
> 
> An internal coding practice that is being addressed bit-by-bit is that
> of managing the interface between the host and the target.  Currently
> this is a bit sloppy and inconsistent (some of which I've contributed
> to).  There are examples of using target addresses for host pointers and
> host errnos for target errnos, using different types between target and
> host that don't sign-extend properly, as well as other things.  This
> causes compiler warnings to actual run-time bugs.  Currently I'm
> reviewing all of the linux-user code (mostly syscall.c) to fix these
> inconsistencies.  I will be writing developer documentation describing
> the coding practices that should govern the target/host interface and
> submitting patches for the fixes.
> 
> As obvious as it may seem I'll re-state that the linux-user emulation is
> emulating the Linux kernel (duh!).  There are portions of qemu
> linux-user that are even excerpted directly from the Linux kernel.
> Consequently it is useful for internal qemu data and functions to
> closely mimic the kernel for best code sharing.  There are also
> advantages to even structuring qemu directly and file organization in
> similar divisions, groupings and locations.  Some of this organization
> might lead to good division so that other user/kernel divisions are
> cleaner (different kernel versions, other OSes - darwin-user and
> others).
> 
> Internal qemu interfaces are consistent - except when they aren't.  This
> causes coding errors when passing target and host arguments or return
> codes.  I'll be documenting the coding practices as well as submitting
> patches to make these consistent.  (That sounds a bit redundant with
> other things I've mentioned).
> 
> I have about 40 patches already worked up that do this.  Some of those
> patches might be broken up smaller.  The qemu that we've been working
> with is nearly rock solid (still a few more bugs being wrung out).  It
> can nearly build an entire Debian arm distribution for an arm target
> being hosted on x86_64.  We're quite excited to get our patches upstream
> so that others can benefit and to ease our maintenance overhead.  We're
> also turning our focus to PPC and other archs.
> 
> Please let me know if you support the general idea of the coding changes
> above: General clean-up, consistent target/host interfaces, file
> splitting/reorganizing, etc..  In the meantime I'll be putting together
> the developer documentation/coding guidelines for review.

FWIW, I agree with everything you said above.


Thiemo