[Qemu-devel] [PATCH 4/8] migration-local: add recv_pipefd()

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

This patch adds recv_pipefd() to receive the pipe file descriptor
that passed by source process.

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 include/migration/qemu-file.h |    1 +
 migration-local.c             |   56 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+), 0 deletions(-)

diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
index 5fad65f..e4df258 100644
--- a/include/migration/qemu-file.h
+++ b/include/migration/qemu-file.h
@@ -102,6 +102,7 @@ QEMUFile *qemu_popen_cmd(const char *command, const char *mode);
 QEMUFile *qemu_fopen_pipe(int sockfd, const char *mode);
 
 int send_pipefd(int sockfd, int pipefd);
+int recv_pipefd(int sockfd);
 int qemu_get_fd(QEMUFile *f);
 int qemu_fclose(QEMUFile *f);
 int64_t qemu_ftell(QEMUFile *f);
diff --git a/migration-local.c b/migration-local.c
index 3875b27..40b8f34 100644
--- a/migration-local.c
+++ b/migration-local.c
@@ -189,3 +189,59 @@ int send_pipefd(int sockfd, int pipefd)
     }
     return 0;
 }
+
+/*
+ * Receive a pipe file descriptor from a source process
+ * via unix socket.
+ *
+ * Return negative value if there has been an recvmsg error or
+ * no fd to be reveived. Return 0 if the connection closed by
+ * source. Return file descriptor on success.
+ *
+ */
+int recv_pipefd(int sockfd)
+{
+    int pipefd;
+    struct cmsghdr *cmsg;
+    struct msghdr msg;
+    struct iovec iov[1];
+    char req[1];
+    int ret;
+    union MsgControl msg_control;
+
+    iov[0].iov_base = req;
+    iov[0].iov_len = sizeof(req);
+
+    memset(&msg, 0, sizeof(msg));
+    msg.msg_iov = iov;
+    msg.msg_iovlen = 1;
+    msg.msg_control = &msg_control;
+    msg.msg_controllen = sizeof(msg_control);
+
+    do {
+        ret = recvmsg(sockfd, &msg, 0);
+    } while (ret < 0 && errno == EINTR);
+    if (ret <= 0) {
+        return ret;
+    }
+
+    /* req 0x01 means there is a file descriptor to receive */
+    if (req[0] != 0x01) {
+        return -1;
+    }
+
+    cmsg = CMSG_FIRSTHDR(&msg);
+    while (cmsg) {
+        if (cmsg->cmsg_level == SOL_SOCKET &&
+            cmsg->cmsg_type == SCM_RIGHTS &&
+            cmsg->cmsg_len == CMSG_LEN(sizeof(int))) {
+
+            /* The file descriptor to be received */
+            memcpy(&pipefd, CMSG_DATA(cmsg), sizeof(pipefd));
+            return pipefd;
+        }
+        cmsg = CMSG_NXTHDR(&msg, cmsg);
+    }
+
+    return -1;
+}
-- 
1.7.7.6