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SubjectRe: [PATCH 0/7] KVM: Kernel-based Virtual Machine
Arnd Bergmann wrote:
> This looks _a_lot_ like what we're doing for the SPUs in the cell processor,
> except that we're using different calls into the kernel. Have you looked
> into what we have implemented there? The code is in
> arch/powerpc/platforms/cell/spufs. I think it would be a good abstraction
> to use for you as well, maybe we could even move to a common infrastructure,
> as I have heard from a few other projects that want to do similar things.
>
> The main differences to your interface are:
>
> - A file system is used instead of a character device
> - Directories, not open file descriptors represent contexts
> - Two new syscalls were introduced (spu_create/spu_run)
> - instead of ioctls, files represent different bits of information,
> you can read/write, poll or mmap them.
>
> Your example above could translate to something like:
>
> int kvm_fd = kvm_create("/kvm/my_vcpu")
> int mem_fd = openat(kvm_fd, "mem", O_RDWR);
> void *mem = mmap(mem_fd, ...); // main memory
> void *fbmem = mmap(mem_fd, ...); // frame buffer memory
> int regs_fd = openat(kvm_fd, "regs", O_RDWR);
> int irq_fd = openat(kvm_fd, "regs", O_WRONLY);
>
> if (debugger) {
> int fd = openat(fvm_fd, "debug", O_WRONLY);
> write(fd, "1", 1);
> close(fd);
> }
> while (1) {
> int exit_reason = kvm_run(kvm_fd, &kvm_descriptor);
> switch (exit reason) {
> handle mmio, I/O etc. might call
> write(irq_fd, &interrupt_packet, sizeof (interrupt_packet));
> pread(regs_fd, &rax, sizeof rax, KVM_REG_RAX);
> }
>

[cc'ing some others to solicit their opinion]


I like this. Since we plan to support multiple vcpus per vm, the fs
structure might look like:

/kvm/my_vm
|
+----memory # mkdir to create memory slot.
| | # how to set size and offset?
| |
| +---0 # guest physical memory slot
| |
| +-- dirty_bitmap # read to get and atomically reset
| # the changed pages log
|
|
+----cpu # mkdir/rmdir to create/remove vcpu
|
+----0
| |
| +--- irq # write to inject an irq
| |
| +--- regs # read/write to get/set registers
| |
| +--- debugger # write to set breakpoints/singlestep mode
|
+----1
[...]

It's certainly a lot more code though, and requires new syscalls. Since
this is a little esoteric does it warrant new syscalls?

--
error compiling committee.c: too many arguments to function

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