virtio-9p: Create a syntactic shortcut for the file-system pass-thru

Currently the commandline to create a virtual-filesystem pass-through between
the guest and the host is as follows:
#qemu -fsdev fstype,id=ID,path=path/to/share \
      -device virtio-9p-pci,fsdev=ID,mount_tag=tag \

This patch provides a syntactic short-cut to achieve the same as follows:
#qemu -virtfs fstype,path=path/to/share,mount_tag=tag

This will be internally expanded as:
#qemu -fsdev fstype,id=tag,path=path/to/share, \
      -device virtio-9p-pci,fsdev=tag,mount_tag=tag \

Signed-off-by: Gautham R Shenoy <ego@in.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

qemu-config.c

@@ -169,6 +169,28 @@ QemuOptsList qemu_fsdev_opts = {
 };
 #endif
 
+#ifdef CONFIG_LINUX
+QemuOptsList qemu_virtfs_opts = {
+    .name = "virtfs",
+    .implied_opt_name = "fstype",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_virtfs_opts.head),
+    .desc = {
+        {
+            .name = "fstype",
+            .type = QEMU_OPT_STRING,
+        }, {
+            .name = "path",
+            .type = QEMU_OPT_STRING,
+        }, {
+            .name = "mount_tag",
+            .type = QEMU_OPT_STRING,
+        },
+
+        { /*End of list */ }
+    },
+};
+#endif
+
 QemuOptsList qemu_device_opts = {
     .name = "device",
     .implied_opt_name = "driver",

qemu-config.h

@@ -5,6 +5,7 @@ extern QemuOptsList qemu_drive_opts;
 extern QemuOptsList qemu_chardev_opts;
 #ifdef CONFIG_LINUX
 extern QemuOptsList qemu_fsdev_opts;
+extern QemuOptsList qemu_virtfs_opts;
 #endif
 extern QemuOptsList qemu_device_opts;
 extern QemuOptsList qemu_netdev_opts;

qemu-options.hx

@@ -510,6 +510,41 @@ Create a file-system-"device" for local-filesystem.
 ETEXI
 #endif
 
+#ifdef CONFIG_LINUX
+DEFHEADING(Virtual File system pass-through options:)
+
+DEF("virtfs", HAS_ARG, QEMU_OPTION_virtfs,
+    "-virtfs local,path=path,mount_tag=tag\n",
+    QEMU_ARCH_ALL)
+
+STEXI
+
+The general form of a Virtual File system pass-through option is:
+@table @option
+
+@item -virtfs @var{fstype} [,@var{options}]
+@findex -virtfs
+Fstype is one of:
+@option{local},
+The specific Fstype will determine the applicable options.
+
+Options to each backend are described below.
+
+@item -virtfs local ,path=@var{path} ,mount_tag=@var{mount_tag}
+
+Create a Virtual file-system-pass through for local-filesystem.
+
+@option{local} is only available on Linux.
+
+@option{path} specifies the path to be exported. @option{path} is required.
+
+@option{mount_tag} specifies the tag with which the exported file is mounted.
+@option{mount_tag} is required.
+
+@end table
+ETEXI
+#endif
+
 DEFHEADING()
 
 DEF("name", HAS_ARG, QEMU_OPTION_name,

vl.c

@@ -3102,6 +3102,62 @@ int main(int argc, char **argv, char **envp)
                     exit(1);
                 }
                 break;
+            case QEMU_OPTION_virtfs: {
+                char *arg_fsdev = NULL;
+                char *arg_9p = NULL;
+                int len = 0;
+
+                opts = qemu_opts_parse(&qemu_virtfs_opts, optarg, 1);
+                if (!opts) {
+                    fprintf(stderr, "parse error: %s\n", optarg);
+                    exit(1);
+                }
+
+                len = strlen(",id=,path=");
+                len += strlen(qemu_opt_get(opts, "fstype"));
+                len += strlen(qemu_opt_get(opts, "mount_tag"));
+                len += strlen(qemu_opt_get(opts, "path"));
+                arg_fsdev = qemu_malloc((len + 1) * sizeof(*arg_fsdev));
+
+                if (!arg_fsdev) {
+                    fprintf(stderr, "No memory to parse -fsdev for %s\n",
+                            optarg);
+                    exit(1);
+                }
+
+                sprintf(arg_fsdev, "%s,id=%s,path=%s",
+                                qemu_opt_get(opts, "fstype"),
+                                qemu_opt_get(opts, "mount_tag"),
+                                qemu_opt_get(opts, "path"));
+
+                len = strlen("virtio-9p-pci,fsdev=,mount_tag=");
+                len += 2*strlen(qemu_opt_get(opts, "mount_tag"));
+                arg_9p = qemu_malloc((len + 1) * sizeof(*arg_9p));
+
+                if (!arg_9p) {
+                    fprintf(stderr, "No memory to parse -device for %s\n",
+                            optarg);
+                    exit(1);
+                }
+
+                sprintf(arg_9p, "virtio-9p-pci,fsdev=%s,mount_tag=%s",
+                                qemu_opt_get(opts, "mount_tag"),
+                                qemu_opt_get(opts, "mount_tag"));
+
+                if (!qemu_opts_parse(&qemu_fsdev_opts, arg_fsdev, 1)) {
+                    fprintf(stderr, "parse error [fsdev]: %s\n", optarg);
+                    exit(1);
+                }
+
+                if (!qemu_opts_parse(&qemu_device_opts, arg_9p, 1)) {
+                    fprintf(stderr, "parse error [device]: %s\n", optarg);
+                    exit(1);
+                }
+
+                qemu_free(arg_fsdev);
+                qemu_free(arg_9p);
+                break;
+            }
 #endif
             case QEMU_OPTION_serial:
                 add_device_config(DEV_SERIAL, optarg);