Re: [Qemu-devel] [PATCH 10/17] migration-local: override save_page for page transmit

[Paolo Bonzini <pbonzini@redhat.com>]

Il 21/11/2013 10:11, Lei Li ha scritto:
> This patch implements save_page callback for the outside
> of page flipping. It will write the address of the page
> on the Unix socket and flip the page data on pipe by
> vmsplice(). Every page address would have a header flag
> RAM_SAVE_FLAG_HOOK, which will trigger the load hook to
> receive it in incoming side as well.
> 
> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
> ---
>  migration-local.c |   54 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 files changed, 54 insertions(+), 0 deletions(-)
> 
> diff --git a/migration-local.c b/migration-local.c
> index 0f0896b..14207e9 100644
> --- a/migration-local.c
> +++ b/migration-local.c
> @@ -200,6 +200,59 @@ static int qemu_local_send_pipefd(QEMUFile *f, void *opaque,
>      return 0;
>  }
>  
> +static size_t qemu_local_save_ram(QEMUFile *f, void *opaque,
> +                                  MemoryRegion *mr, ram_addr_t offset,
> +                                  size_t size, int *bytes_sent)
> +{
> +    QEMUFileLocal *s = opaque;
> +    ram_addr_t current_addr = mr->ram_addr + offset;
> +    void *ram_addr;
> +    ssize_t ret;
> +
> +    if (s->unix_page_flipping) {
> +        qemu_fflush(s->file);
> +        qemu_put_be64(s->file, RAM_SAVE_FLAG_HOOK);
> +
> +        /* Write page address to unix socket */
> +        qemu_put_be64(s->file, current_addr);
> +

You can write current_addr | RAM_SAVE_FLAG_HOOK.  The value will be in
the flags argument of the hook_ram_load, you can extract it with "flags
& ~RAM_SAVE_FLAG_HOOK".  This cuts by half the data written to the Unix
socket.

Paolo

> +        ram_addr = memory_region_get_ram_ptr(mr) + offset;
> +
> +        /* vmsplice page data to pipe */
> +        struct iovec iov = {
> +            .iov_base = ram_addr,
> +            .iov_len  = size,
> +        };
> +
> +        /*
> +         * The flag SPLICE_F_MOVE is introduced in kernel for the page
> +         * flipping feature in QEMU, which will movie pages rather than
> +         * copying, previously unused.
> +         *
> +         * If a move is not possible the kernel will transparently falls
> +         * back to copying data.
> +         *
> +         * For older kernels the SPLICE_F_MOVE would be ignored and a copy
> +         * would occur.
> +         */
> +        ret = vmsplice(s->pipefd[1], &iov, 1, SPLICE_F_GIFT | SPLICE_F_MOVE);
> +        if (ret == -1) {
> +            if (errno != EAGAIN && errno != EINTR) {
> +                fprintf(stderr, "vmsplice save error: %s\n", strerror(errno));
> +                return ret;
> +            }
> +        } else {
> +            if (bytes_sent) {
> +                *bytes_sent = 1;
> +            }
> +            DPRINTF("block_offset: %lu, offset: %lu\n", block_offset, offset);
> +            return 0;
> +        }
> +    }
> +
> +    return RAM_SAVE_CONTROL_NOT_SUPP;
> +}
> +
>  static const QEMUFileOps pipe_read_ops = {
>      .get_fd        = qemu_local_get_sockfd,
>      .get_buffer    = qemu_local_get_buffer,
> @@ -211,6 +264,7 @@ static const QEMUFileOps pipe_write_ops = {
>      .writev_buffer      = qemu_local_writev_buffer,
>      .close              = qemu_local_close,
>      .before_ram_iterate = qemu_local_send_pipefd,
> +    .save_page          = qemu_local_save_ram
>  };
>  
>  QEMUFile *qemu_fopen_socket_local(int sockfd, const char *mode)
>