[Qemu-devel] [PATCH 4/5] Add domain socket communication for vhost-user backend

[Antonios Motakis]

Add structures for passing vhost-user messages over a unix domain socket.
This is the equivalent of the existing vhost-kernel ioctls.

Connect to the named unix domain socket. The system call sendmsg
is used for communication. To be able to pass file descriptors
between processes - we use SCM_RIGHTS type in the message control header.

Signed-off-by: Antonios Motakis <address@hidden>
Signed-off-by: Nikolay Nikolaev <address@hidden>
---
 hw/virtio/vhost-backend.c | 164 +++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 162 insertions(+), 2 deletions(-)

diff --git a/hw/virtio/vhost-backend.c b/hw/virtio/vhost-backend.c
index 80defe4..264a0a1 100644
--- a/hw/virtio/vhost-backend.c
+++ b/hw/virtio/vhost-backend.c
@@ -15,6 +15,115 @@
 #include <fcntl.h>
 #include <unistd.h>
 #include <sys/ioctl.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <linux/vhost.h>
+
+#define VHOST_MEMORY_MAX_NREGIONS    8
+
+typedef enum VhostUserRequest {
+    VHOST_USER_NONE = 0,
+    VHOST_USER_GET_FEATURES = 1,
+    VHOST_USER_SET_FEATURES = 2,
+    VHOST_USER_SET_OWNER = 3,
+    VHOST_USER_RESET_OWNER = 4,
+    VHOST_USER_SET_MEM_TABLE = 5,
+    VHOST_USER_SET_LOG_BASE = 6,
+    VHOST_USER_SET_LOG_FD = 7,
+    VHOST_USER_SET_VRING_NUM = 8,
+    VHOST_USER_SET_VRING_ADDR = 9,
+    VHOST_USER_SET_VRING_BASE = 10,
+    VHOST_USER_GET_VRING_BASE = 11,
+    VHOST_USER_SET_VRING_KICK = 12,
+    VHOST_USER_SET_VRING_CALL = 13,
+    VHOST_USER_SET_VRING_ERR = 14,
+    VHOST_USER_NET_SET_BACKEND = 15,
+    VHOST_USER_MAX
+} VhostUserRequest;
+
+typedef struct VhostUserMemoryRegion {
+    __u64 guest_phys_addr;
+    __u64 memory_size;
+    __u64 userspace_addr;
+} VhostUserMemoryRegion;
+
+typedef struct VhostUserMemory {
+    __u32 nregions;
+    VhostUserMemoryRegion regions[VHOST_MEMORY_MAX_NREGIONS];
+} VhostUserMemory;
+
+typedef struct VhostUserMsg {
+    VhostUserRequest request;
+
+    int flags;
+    union {
+        uint64_t    u64;
+        int         fd;
+        struct vhost_vring_state state;
+        struct vhost_vring_addr addr;
+        struct vhost_vring_file file;
+
+        VhostUserMemory memory;
+    };
+} VhostUserMsg;
+
+static int vhost_user_recv(int fd, VhostUserMsg *msg)
+{
+    ssize_t r = read(fd, msg, sizeof(VhostUserMsg));
+
+    return (r == sizeof(VhostUserMsg)) ? 0 : -1;
+}
+
+static int vhost_user_send_fds(int fd, const VhostUserMsg *msg, int *fds,
+        size_t fd_num)
+{
+    int ret;
+
+    struct msghdr msgh;
+    struct iovec iov[1];
+
+    size_t fd_size = fd_num * sizeof(int);
+    char control[CMSG_SPACE(fd_size)];
+    struct cmsghdr *cmsg;
+
+    memset(&msgh, 0, sizeof(msgh));
+    memset(control, 0, sizeof(control));
+
+    /* set the payload */
+    iov[0].iov_base = (void *) msg;
+    iov[0].iov_len = sizeof(VhostUserMsg);
+
+    msgh.msg_iov = iov;
+    msgh.msg_iovlen = 1;
+
+    if (fd_num) {
+        msgh.msg_control = control;
+        msgh.msg_controllen = sizeof(control);
+
+        cmsg = CMSG_FIRSTHDR(&msgh);
+
+        cmsg->cmsg_len = CMSG_LEN(fd_size);
+        cmsg->cmsg_level = SOL_SOCKET;
+        cmsg->cmsg_type = SCM_RIGHTS;
+        memcpy(CMSG_DATA(cmsg), fds, fd_size);
+    } else {
+        msgh.msg_control = 0;
+        msgh.msg_controllen = 0;
+    }
+
+    do {
+        ret = sendmsg(fd, &msgh, 0);
+    } while (ret < 0 && errno == EINTR);
+
+    if (ret < 0) {
+        fprintf(stderr, "Failed to send msg(%d), reason: %s\n",
+                msg->request, strerror(errno));
+    } else {
+        ret = 0;
+    }
+
+    return ret;
+}
 
 static int vhost_kernel_call(struct vhost_dev *dev, unsigned long int request,
         void *arg)
@@ -23,6 +132,39 @@ static int vhost_kernel_call(struct vhost_dev *dev, 
unsigned long int request,
     return ioctl(fd, request, arg);
 }
 
+static int vhost_user_call(struct vhost_dev *dev, unsigned long int request,
+        void *arg)
+{
+    int fd = dev->control;
+    VhostUserMsg msg;
+    int result = 0;
+    int fds[VHOST_MEMORY_MAX_NREGIONS];
+    size_t fd_num = 0;
+
+    memset(&msg, 0, sizeof(VhostUserMsg));
+
+    switch (request) {
+    default:
+        fprintf(stderr, "vhost-user trying to send unhandled ioctl\n");
+        return -1;
+        break;
+    }
+
+    result = vhost_user_send_fds(fd, &msg, fds, fd_num);
+
+    if (!result) {
+        result = vhost_user_recv(fd, &msg);
+        if (!result) {
+            switch (request) {
+            default:
+                fprintf(stderr, "vhost-user received unhandled message\n");
+            }
+        }
+    }
+
+    return result;
+}
+
 int vhost_call(struct vhost_dev *dev, unsigned long int request, void *arg)
 {
     int result = -1;
@@ -32,7 +174,7 @@ int vhost_call(struct vhost_dev *dev, unsigned long int 
request, void *arg)
         result = vhost_kernel_call(dev, request, arg);
         break;
     case VHOST_BACKEND_TYPE_USER:
-        fprintf(stderr, "vhost-user not implemented\n");
+        result = vhost_user_call(dev, request, arg);
         break;
     default:
         fprintf(stderr, "Unknown vhost backend type\n");
@@ -44,13 +186,31 @@ int vhost_call(struct vhost_dev *dev, unsigned long int 
request, void *arg)
 int vhost_backend_init(struct vhost_dev *dev, const char *devpath)
 {
     int fd = -1;
+    struct sockaddr_un un;
+    size_t len;
 
     switch (dev->backend_type) {
     case VHOST_BACKEND_TYPE_KERNEL:
         fd = open(devpath, O_RDWR);
         break;
     case VHOST_BACKEND_TYPE_USER:
-        fprintf(stderr, "vhost-user not implemented\n");
+        /* Create the socket */
+        fd = socket(AF_UNIX, SOCK_STREAM, 0);
+        if (fd == -1) {
+            perror("socket");
+            return -1;
+        }
+
+        un.sun_family = AF_UNIX;
+        strcpy(un.sun_path, devpath);
+
+        len = sizeof(un.sun_family) + strlen(devpath);
+
+        /* Connect */
+        if (connect(fd, (struct sockaddr *) &un, len) == -1) {
+            perror("connect");
+            return -1;
+        }
         break;
     default:
         fprintf(stderr, "Unknown vhost backend type\n");
-- 
1.8.3.2