Re: [Qemu-devel] [PATCH 08/17] add unix_msgfd_lookup() to callback get_buffer

[Lei Li]

On 11/21/2013 05:11 PM, Lei Li wrote:
> The control message for exchange of pipe file descriptor should
> be received by recvmsg, and it might be eaten to stream file by
> qemu_recv() when receiving by two callbacks. So this patch adds
> unix_msgfd_lookup() to callback get_buffer as the only one receiver,
> where the pipe file descriptor would be caughted.
>
> Signed-off-by: Lei Li <address@hidden>
> ---
>   migration-local.c |   68 ++++++++++++++++++++++++++++++++++++++++++++++++++--
>   1 files changed, 65 insertions(+), 3 deletions(-)
>
> diff --git a/migration-local.c b/migration-local.c
> index e028beb..0f0896b 100644
> --- a/migration-local.c
> +++ b/migration-local.c
> @@ -50,6 +50,8 @@ typedef struct QEMUFileLocal {
>       bool unix_page_flipping;
>   } QEMUFileLocal;
>
> +static bool pipefd_passed;
> +
>   static int qemu_local_get_sockfd(void *opaque)
>   {
>       QEMUFileLocal *s = opaque;
> @@ -57,16 +59,76 @@ static int qemu_local_get_sockfd(void *opaque)
>       return s->sockfd;
>   }
>
> +static int unix_msgfd_lookup(void *opaque, struct msghdr *msg)
> +{
> +    QEMUFileLocal *s = opaque;
> +    struct cmsghdr *cmsg;
> +    bool found = false;
> +
> +    for (cmsg = CMSG_FIRSTHDR(msg); cmsg; cmsg = CMSG_NXTHDR(msg, cmsg)) {
> +        if (cmsg->cmsg_len != CMSG_LEN(sizeof(int)) ||
> +            cmsg->cmsg_level != SOL_SOCKET ||
> +            cmsg->cmsg_type != SCM_RIGHTS)
> +            continue;
> +
> +        /* PIPE file descriptor to be received */
> +        s->pipefd[0] = *((int *)CMSG_DATA(cmsg));
> +    }
> +
> +    if (s->pipefd[0] <= 0) {

And this should be if (s->pipefd[0] < 0)..

> +        fprintf(stderr, "no pipe fd can be received\n");
> +        return found;
> +    }
> +
> +    DPRINTF("pipefd successfully received\n");
> +    return s->pipefd[0];
> +}
> +
>   static int qemu_local_get_buffer(void *opaque, uint8_t *buf,
>                                    int64_t pos, int size)
>   {
>       QEMUFileLocal *s = opaque;
>       ssize_t len;
> +    struct msghdr msg = { NULL, };
> +    struct iovec iov[1];
> +    union {
> +        struct cmsghdr cmsg;
> +        char control[CMSG_SPACE(sizeof(int))];
> +    } msg_control;
> +
> +    iov[0].iov_base = buf;
> +    iov[0].iov_len = size;
> +
> +    msg.msg_iov = iov;
> +    msg.msg_iovlen = 1;
> +    msg.msg_control = &msg_control;
> +    msg.msg_controllen = sizeof(msg_control);
>
>       for (;;) {
> -        len = qemu_recv(s->sockfd, buf, size, 0);
> -        if (len != -1) {
> -            break;
> +        if (!pipefd_passed) {
> +            /*
> +             * recvmsg is called here to catch the control message for
> +             * the exchange of PIPE file descriptor until it is received.
> +             */
> +            len = recvmsg(s->sockfd, &msg, 0);
> +            if (len != -1) {
> +                if (unix_msgfd_lookup(s, &msg) > 0) {
> +                    pipefd_passed = 1;
> +                    /*
> +                     * Do not count one byte taken by the PIPE file
> +                     * descriptor.
> +                     */
> +                    len--;
> +                } else {
> +                    len = -1;
> +                }

Just found that this 'else' should go away as it will break the normal
Unix migration since pipefd_passed will always be 0 for it. I have
fixed this in my code, seems I mis-send it for some reason, sorry
for this...:-[  

> +                break;
> +            }
> +        } else {
> +            len = qemu_recv(s->sockfd, buf, size, 0);
> +            if (len != -1) {
> +                break;
> +            }
>           }
>
>           if (socket_error() == EAGAIN) {


--
Lei