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Re: [libvirt] [PATCHv4 05/15] util: use SCM_RIGHTS in virFileOperation when needed



On Wed, Mar 09, 2011 at 06:45:45PM -0700, Eric Blake wrote:
> Currently, the hook function in virFileOperation is extremely limited:
> it must be async-signal-safe, and cannot modify any memory in the
> parent process.  It is much handier to return a valid fd and operate
> on it in the parent than to deal with hook restrictions.
> 
> * src/util/util.h (VIR_FILE_OP_RETURN_FD): New flag.
> * src/util/util.c (virFileOperationNoFork, virFileOperation):
> Honor new flag.
> ---
>  src/util/util.c |  139 ++++++++++++++++++++++++++++++++++++++++++++++++------
>  src/util/util.h |    4 +-
>  2 files changed, 126 insertions(+), 17 deletions(-)

ACK,

> +        memset(&msg, 0, sizeof(msg));
> +        iov.iov_base = &dummy;
> +        iov.iov_len = 1;
> +        msg.msg_iov = &iov;
> +        msg.msg_iovlen = 1;
> +        msg.msg_control = buf;
> +        msg.msg_controllen = sizeof(buf);
> +        cmsg = CMSG_FIRSTHDR(&msg);
> +        cmsg->cmsg_level = SOL_SOCKET;
> +        cmsg->cmsg_type = SCM_RIGHTS;
> +        cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
> +    }

....

> +        if (flags & VIR_FILE_OP_RETURN_FD) {
> +            VIR_FORCE_CLOSE(pair[1]);
> +
> +            do {
> +                ret = recvmsg(pair[0], &msg, 0);
> +            } while (ret < 0 && errno == EINTR);
> +
> +            if (ret < 0) {
> +                ret = -errno;
> +                VIR_FORCE_CLOSE(pair[0]);
> +                while ((waitret = waitpid(pid, NULL, 0) == -1)
> +                       && (errno == EINTR));
> +                goto parenterror;
> +            }
> +            VIR_FORCE_CLOSE(pair[0]);
> +
> +            /* See if fd was transferred.  */
> +            cmsg = CMSG_FIRSTHDR(&msg);
> +            if (cmsg && cmsg->cmsg_len == CMSG_LEN(sizeof(fd)) &&
> +                cmsg->cmsg_level == SOL_SOCKET &&
> +                cmsg->cmsg_type == SCM_RIGHTS) {
> +                memcpy(&fd, CMSG_DATA(cmsg), sizeof(fd));
> +            }

Also might be nice to create two helper methods for this

  int virFileHandleSendToSocket(int unixfd, int sendfd);
  int virFileHandleRecvFromSocket(int unixfd);

which we can also use in the monitor code that does the
same thing


Daniel
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