Re: [Qemu-devel] [PATCH 06/17] migration-local: add send_pipefd()

[Lei Li <lilei@linux.vnet.ibm.com>]

On 12/03/2013 07:52 PM, Paolo Bonzini wrote:
> Il 03/12/2013 12:19, Lei Li ha scritto:
>> On 12/02/2013 05:33 PM, Daniel P. Berrange wrote:
>>> On Mon, Dec 02, 2013 at 05:19:06PM +0800, Lei Li wrote:
>>>> This patch adds send_pipefd() to pass the pipe file descriptor
>>>> to destination process.
>>>>
>>>> Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
>>>> ---
>>>>    migration-local.c |   46
>>>> ++++++++++++++++++++++++++++++++++++++++++++++
>>>>    1 files changed, 46 insertions(+), 0 deletions(-)
>>>>
>>>> diff --git a/migration-local.c b/migration-local.c
>>>> index 929ed60..f479530 100644
>>>> --- a/migration-local.c
>>>> +++ b/migration-local.c
>>>> @@ -167,3 +167,49 @@ fail:
>>>>        g_free(s);
>>>>        return NULL;
>>>>    }
>>>> +
>>>> +
>>>> +/*
>>>> + * Pass a pipe file descriptor to another process.
>>>> + *
>>>> + * Return negative value If pipefd < 0. Return 0 on
>>>> + * success.
>>>> + *
>>>> + */
>>>> +static int send_pipefd(int sockfd, int pipefd)
>>>> +{
>>>> +    struct msghdr msg;
>>>> +    struct iovec iov[1];
>>>> +    ssize_t ret;
>>>> +    char req[1] = { 0x01 };
>>>> +
>>>> +    union {
>>>> +      struct cmsghdr cm;
>>>> +      char control[CMSG_SPACE(sizeof(int))];
>>>> +    } control_un;
>>>> +    struct cmsghdr *cmptr;
>>>> +
>>>> +    msg.msg_control = control_un.control;
>>>> +    msg.msg_controllen = sizeof(control_un.control);
>>>> +
>>>> +    cmptr = CMSG_FIRSTHDR(&msg);
>>>> +    cmptr->cmsg_len = CMSG_LEN(sizeof(int));
>>>> +    cmptr->cmsg_level = SOL_SOCKET;
>>>> +    cmptr->cmsg_type = SCM_RIGHTS;
>>>> +    *((int *) CMSG_DATA(cmptr)) = pipefd;
>>>> +
>>>> +    msg.msg_name = NULL;
>>>> +    msg.msg_namelen = 0;
>>>> +
>>>> +    iov[0].iov_base = req;
>>>> +    iov[0].iov_len = sizeof(req);
>>>> +    msg.msg_iov = iov;
>>>> +    msg.msg_iovlen = 1;
>>>> +
>>>> +    ret = sendmsg(sockfd, &msg, 0);
>>>> +    if (ret <= 0) {
>>>> +        DPRINTF("sendmsg error: %s\n", strerror(errno));
>>>> +    }
>>>> +
>>>> +    return ret;
>>>> +}
>>> Just a reminder about my comments from previous posting. This is
>>> introducing a 3rd private function for sending FDs. The existing
>>> code should be refactored into qemu-socket.{c,h} and shared.
>> Hi Daniel,
>>
>> Yes, I remembered your suggestion. As my reply in the previous version,
>> I'll make this refactoring in a separate thread. There are some differences
>> between these private functions (like data type and length of bytes
>> transmitted), may need a little time to get the common method settle down,
>> and would be better to do some test to make sure there is no impact on
>> them.
> You would have to implement it in such a way that the buffer is
> specified in the function, for example:
>
> ssize_t qemu_send_with_fd(int sockfd, int passed_fd, const void *buf,
>                            size_t len);
> ssize_t qemu_recv_with_fd(int sockfd, int *passed_fd, void *buf,
>                            size_t len);
>
> The functions can go in util/ (I think not in qemu-socket.c, a new file
> is preferrable).
>
> I don't think it's particularly important, but it's definitely welcome.

Hi Paolo,

Thanks for your specified suggestion! As it needs to test the related
code (tap/bridge & Proxy FS & flipping migration), I will work on it
after back from my vacation next week.  :-)

>
> Paolo
>


-- 
Lei