[Qemu-devel] [PATCH][v2] inetd enabled qemu-nbd

[Jun Sheng <chaoseternal@gmail.com>]

run qemu-nbd as an inetd service has some benefits
* more scriptable, such as serve multiple images to different clients
on one ip/port
* access control using tcpd

simple usage:
#!/bin/sh
# qemu-nbd wrapper, select image file according to client ip address
IMG_FILE=`sed -n "s/$REMOTE_HOST //p" /path/to/image_list.txt`
qemu-nbd -i 10 $IMG_FILE 10<&0- 1>/tmp/log 2>/tmp/log2

#end

#xinetd.conf
service nbd
{
        flags                   = REUSE
        socket_type             = stream
        wait                    = no
        user                    = some_user
        server                  = /path/to/qemu-nbd-wrapper.sh
        log_on_failure          += USERID
        disable                 = no
}

Signed-off-by: Jun Sheng <chaoseternal@gmail.com>

---
 qemu-nbd.c | 42 ++++++++++++++++++++++++++++++++++--------
 1 file changed, 34 insertions(+), 8 deletions(-)

diff --git a/qemu-nbd.c b/qemu-nbd.c
index 5cd6c6d..f4af4c7 100644
--- a/qemu-nbd.c
+++ b/qemu-nbd.c
@@ -49,6 +49,7 @@ static NBDExport *exp;
 static int verbose;
 static char *srcpath;
 static char *sockpath;
+static int inetd_fd = -1;
 static int persistent = 0;
 static enum { RUNNING, TERMINATE, TERMINATING, TERMINATED } state;
 static int shared = 1;
@@ -66,6 +67,7 @@ static void usage(const char *name)
 "Connection properties:\n"
 "  -p, --port=PORT           port to listen on (default `%d')\n"
 "  -b, --bind=IFACE          interface to bind to (default `0.0.0.0')\n"
+"  -i, --inetd=FD            run as an inetd services on FD\n"
 "  -k, --socket=PATH         path to the unix socket\n"
 "                            (default '"SOCKET_PATH"')\n"
 "  -e, --shared=NUM          device can be shared by NUM clients (default '1')\n"
@@ -363,7 +365,13 @@ static void nbd_accept(void *opaque)
     struct sockaddr_in addr;
     socklen_t addr_len = sizeof(addr);
 
-    int fd = accept(server_fd, (struct sockaddr *)&addr, &addr_len);
+    int fd;
+    if (inetd_fd < 0) {
+        fd = accept(server_fd, (struct sockaddr *)&addr, &addr_len);
+    } else {
+        fd = server_fd;
+    }
+
     if (fd < 0) {
         perror("accept");
         return;
@@ -396,10 +404,11 @@ int main(int argc, char **argv)
     off_t fd_size;
     QemuOpts *sn_opts = NULL;
     const char *sn_id_or_name = NULL;
-    const char *sopt = "hVb:o:p:rsnP:c:dvk:e:f:tl:";
+    const char *sopt = "hVi:b:o:p:rsnP:c:dvk:e:f:tl:";
     struct option lopt[] = {
         { "help", 0, NULL, 'h' },
         { "version", 0, NULL, 'V' },
+        { "inetd", 1, NULL, 'i'},
         { "bind", 1, NULL, 'b' },
         { "port", 1, NULL, 'p' },
         { "socket", 1, NULL, 'k' },
@@ -508,6 +517,16 @@ int main(int argc, char **argv)
                                    "without setting discard operation to unmap"); 
             }
             break;
+        case 'i':
+            inetd_fd = qemu_parse_fd(optarg);
+            if (inetd_fd < 0) {
+                errx(EXIT_FAILURE, "Invalid inet fd `%s'", optarg);
+            }
+            if (inetd_fd <= STDERR_FILENO) {
+                errx(EXIT_FAILURE, "Inet fd out of range `%s',"
+                                   " should be in [3, 65535]", optarg);
+            }
+            break;
         case 'b':
             bindto = optarg;
             break;
@@ -732,10 +751,14 @@ int main(int argc, char **argv)
 
     exp = nbd_export_new(bs, dev_offset, fd_size, nbdflags, nbd_export_closed);
 
-    if (sockpath) {
-        fd = unix_socket_incoming(sockpath);
+    if (inetd_fd < 0) {
+        if (sockpath) {
+            fd = unix_socket_incoming(sockpath);
+        } else {
+            fd = tcp_socket_incoming(bindto, port);
+        }
     } else {
-        fd = tcp_socket_incoming(bindto, port);
+        fd = inetd_fd;
     }
 
     if (fd < 0) {
@@ -754,9 +777,12 @@ int main(int argc, char **argv)
         /* Shut up GCC warnings.  */
         memset(&client_thread, 0, sizeof(client_thread));
     }
-
-    qemu_set_fd_handler2(fd, nbd_can_accept, nbd_accept, NULL,
-                         (void *)(uintptr_t)fd);
+    if (inetd_fd < 0) {
+        qemu_set_fd_handler2(fd, nbd_can_accept, nbd_accept, NULL,
+                             (void *)(uintptr_t)fd);
+    } else {
+        nbd_accept((void *)(uintptr_t)fd);
+    }
 
     /* now when the initialization is (almost) complete, chdir("/")
      * to free any busy filesystems */
-- 
2.1.2