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Date: Mon, 15 Aug 2011 12:29:37 -0700
From: Avi Kivity <avi@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH][RFC] post copy chardevice (was Re: [RFC]
 postcopy livemigration proposal)
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To: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: Andrea Arcangeli <aarcange@redhat.com>, Nadav Har'El <nyh@math.technion.ac.il>, kvm@vger.kernel.org, satoshi.itoh@aist.go.jp, Stefan Hajnoczi <stefanha@gmail.com>, t.hirofuchi@aist.go.jp, Dor Laor <dlaor@redhat.com>, qemu-devel@nongnu.org, Yaniv Kaul <ykaul@redhat.com>

On 08/12/2011 04:07 AM, Isaku Yamahata wrote:
> This is a character device to hook page access.
> The page fault in the area is reported to another user process by
> this chardriver. Then, the process fills the page contents and
> resolves the page fault.

Have you considered CUSE (character device in userspace, fs/fuse/cuse.c)?

> index 55f5afb..623109e 100644
> --- a/include/linux/kvm.h
> +++ b/include/linux/kvm.h
> @@ -554,6 +554,7 @@ struct kvm_ppc_pvinfo {
>   #define KVM_CAP_PPC_SMT 64
>   #define KVM_CAP_PPC_RMA	65
>   #define KVM_CAP_MAX_VCPUS 66       /* returns max vcpus per vm */
> +#define KVM_CAP_POST_COPY_MEMORY 67
>
>   #ifdef KVM_CAP_IRQ_ROUTING
>
> @@ -760,6 +761,50 @@ struct kvm_clock_data {
>   /* Available with KVM_CAP_RMA */
>   #define KVM_ALLOCATE_RMA	  _IOR(KVMIO,  0xa9, struct kvm_allocate_rma)
>
> +struct kvm_vmem_create {
> +	__u64 size;	/* in bytes */
> +	__s32 vmem_fd;
> +	__s32 shmem_fd;
> +};

Should really be outside kvm.h (and virt/kvm), since it's not kvm specific.

> +
> +struct kvm_vmem_page_request {
> +	__u32 nr;
> +	__u64 __user *pgoffs;
> +};
> +
> +struct kvm_vmem_page_cached {
> +	__u32 nr;
> +	__u64 __user *pgoffs;
> +};
> +
> +struct kvm_vmem_page_range {
> +	__u64 pgoff;
> +	__u64 nr_pages;
> +};
> +
> +struct kvm_vmem_make_pages_present {
> +	__u32 nr;
> +	struct kvm_vmem_page_range __user *ranges;
> +};

This is madvise(MADV_WILLNEED), is it not?

> +
> +/* Available with KVM_CAP_POST_COPY_MEMORY */
> +#define KVM_CREATE_VMEM_DEV       _IO(KVMIO,  0xb0)
> +
> +/* ioctl for vmem_dev fd */
> +#define KVM_CREATE_VMEM		  _IOR(KVMIO, 0xb1, __u32)
> +
> +/* ioctl for vmem fd */
> +#define KVM_VMEM_WAIT_READY	  _IO(KVMIO,  0xb2)
> +#define KVM_VMEM_READY		  _IO(KVMIO,  0xb3)
> +#define KVM_VMEM_GET_PAGE_REQUEST \
> +	_IOWR(KVMIO, 0xb4, struct kvm_vmem_page_request)
> +#define KVM_VMEM_MARK_PAGE_CACHED \
> +	_IOW(KVMIO,  0xb5, struct kvm_vmem_page_cached)
> +#define KVM_VMEM_MAKE_PAGES_PRESENT \
> +	_IOW(KVMIO,  0xb6, struct kvm_vmem_make_pages_present)
> +#define KVM_VMEM_MAKE_VMA_ANONYMOUS _IO(KVMIO, 0xb7)

Can you explain these in some more detail?

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.