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Date: Tue, 26 Nov 2013 12:25:09 +0100
From: Paolo Bonzini <pbonzini@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH 12/17] migration-local: override
	hook_ram_load
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To: Lei Li <lilei@linux.vnet.ibm.com>
Cc: aarcange@redhat.com, quintela@redhat.com, mdroth@linux.vnet.ibm.com, mrhines@linux.vnet.ibm.com, qemu-devel@nongnu.org, aliguori@amazon.com, lagarcia@br.ibm.com, rcj@linux.vnet.ibm.com

Il 21/11/2013 10:11, Lei Li ha scritto:
> +static int qemu_local_ram_load(QEMUFile *f, void *opaque,
> +                               uint64_t flags)
> +{
> +    QEMUFileLocal *s = opaque;
> +    ram_addr_t addr;
> +    struct iovec iov;
> +    ssize_t ret = -EINVAL;
> +
> +    /*
> +     * PIPE file descriptor will be received by another callback
> +     * get_buffer.
> +     */
> +    if (pipefd_passed) {
> +        void *host;
> +        /*
> +         * Extract the page address from the 8-byte record and
> +         * read the page data from the pipe.
> +         */
> +        addr = qemu_get_be64(s->file);
> +        host = qemu_get_ram_ptr(addr);
> +
> +        iov.iov_base = host;
> +        iov.iov_len = TARGET_PAGE_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[0], &iov, 1, SPLICE_F_MOVE);
> +        if (ret == -1) {
> +            if (errno != EAGAIN && errno != EINTR) {
> +                fprintf(stderr, "vmsplice() load error: %s", strerror(errno));
> +                return ret;
> +            }
> +            DPRINTF("vmsplice load error\n");
> +        } else if (ret == 0) {
> +            DPRINTF(stderr, "load_page: zero read\n");
> +        }
> +
> +        DPRINTF("vmsplice (read): %zu\n", ret);
> +        return ret;
> +    }
> +
> +    return 0;
> +}

I think you need to return -EINVAL if there is no pipe.

Paolo