[Qemu-devel] [PATCH v2 3/3] qemu-config: Add new -add-fd command line option

[Corey Bryant <coreyb@linux.vnet.ibm.com>]

This option can be used for passing file descriptors on the
command line.  It mirrors the existing add-fd QMP command which
allows an fd to be passed to QEMU via SCM_RIGHTS and added to an
fd set.

This can be combined with commands such as -drive to link file
descriptors in an fd set to a drive:

    qemu-kvm -add-fd fd=4,set=2,opaque="rdwr:/path/to/file"
             -add-fd fd=5,set=2,opaque="rdonly:/path/to/file"
             -drive file=/dev/fdset/2,index=0,media=disk

This example adds fds 4 and 5, and the accompanying opaque
strings to the fd set with ID=2.  qemu_open() already knows how
to handle a filename of this format.  qemu_open() searches the
corresponding fd set for an fd and when it finds a match, QEMU
goes on to use a dup of that fd just like it would have used an
fd that it opened itself.

Signed-off-by: Corey Bryant <coreyb@linux.vnet.ibm.com>
---
v2:
 - The -add-fd option is new in v2 (eblake@redhat.com)

 qemu-config.c   | 22 ++++++++++++++++++++++
 qemu-options.hx | 35 +++++++++++++++++++++++++++++++++++
 vl.c            | 36 ++++++++++++++++++++++++++++++++++++
 3 files changed, 93 insertions(+)

diff --git a/qemu-config.c b/qemu-config.c
index cd1ec21..0bd67ca 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -653,6 +653,27 @@ QemuOptsList qemu_boot_opts = {
     },
 };
 
+static QemuOptsList qemu_add_fd_opts = {
+    .name = "add-fd",
+    .head = QTAILQ_HEAD_INITIALIZER(qemu_add_fd_opts.head),
+    .desc = {
+        {
+            .name = "fd",
+            .type = QEMU_OPT_NUMBER,
+            .help = "file descriptor to add to fd set",
+        },{
+            .name = "set",
+            .type = QEMU_OPT_NUMBER,
+            .help = "ID of the fd set to add fd to",
+        },{
+            .name = "opaque",
+            .type = QEMU_OPT_STRING,
+            .help = "free-form string used to describe fd",
+        },
+        { /* end of list */ }
+    },
+};
+
 static QemuOptsList *vm_config_groups[32] = {
     &qemu_drive_opts,
     &qemu_chardev_opts,
@@ -669,6 +690,7 @@ static QemuOptsList *vm_config_groups[32] = {
     &qemu_boot_opts,
     &qemu_iscsi_opts,
     &qemu_sandbox_opts,
+    &qemu_add_fd_opts,
     NULL,
 };
 
diff --git a/qemu-options.hx b/qemu-options.hx
index 7d97f96..884fcb6 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -257,6 +257,14 @@ qemu-system-i386 -drive file=file,index=2,media=disk
 qemu-system-i386 -drive file=file,index=3,media=disk
 @end example
 
+You can open an image using pre-opened file descriptors from an fd set:
+@example
+qemu-system-i386
+-add-fd fd=4,set=2,opaque="rdwr:/path/to/file"
+-add-fd fd=5,set=2,opaque="rdonly:/path/to/file"
+-drive file=/dev/fdset/2,index=0,media=disk
+@end example
+
 You can connect a CDROM to the slave of ide0:
 @example
 qemu-system-i386 -drive file=file,if=ide,index=1,media=cdrom
@@ -289,6 +297,33 @@ qemu-system-i386 -hda a -hdb b
 @end example
 ETEXI
 
+DEF("add-fd", HAS_ARG, QEMU_OPTION_add_fd,
+    "-add-fd fd=fd,set=set[,opaque=opaque]\n"
+    "                Add 'fd' to fd 'set'\n", QEMU_ARCH_ALL)
+STEXI
+@item -add-fd fd=@var{fd},set=@var{set}[,opaque=@var{opaque}]
+@findex -add-fd
+
+Add a file descriptor to an fd set.  Valid options are:
+
+@table @option
+@item fd=@var{fd}
+This option defines the file descriptor that is to be added to the fd set.
+@item set=@var{set}
+This option defines the ID of the fd set to add the file descriptor to.
+@item opaque=@var{opaque}
+This option defines a free-form string that can be used to describe @var{fd}.
+@end table
+
+You can open an image using pre-opened file descriptors from an fd set:
+@example
+qemu-system-i386
+-add-fd fd=4,set=2,opaque="rdwr:/path/to/file"
+-add-fd fd=5,set=2,opaque="rdonly:/path/to/file"
+-drive file=/dev/fdset/2,index=0,media=disk
+@end example
+ETEXI
+
 DEF("set", HAS_ARG, QEMU_OPTION_set,
     "-set group.id.arg=value\n"
     "                set <arg> parameter for item <id> of type <group>\n"
diff --git a/vl.c b/vl.c
index 8d305ca..0265712 100644
--- a/vl.c
+++ b/vl.c
@@ -790,6 +790,33 @@ static int parse_sandbox(QemuOpts *opts, void *opaque)
     return 0;
 }
 
+static int parse_add_fd(QemuOpts *opts, void *opaque)
+{
+    int fd;
+    int64_t fdset_id;
+    const char *fd_opaque = NULL;
+
+    fd = qemu_opt_get_number(opts, "fd", -1);
+    fdset_id = qemu_opt_get_number(opts, "set", -1);
+    fd_opaque = qemu_opt_get(opts, "opaque");
+
+    if (fd == -1) {
+        qerror_report(ERROR_CLASS_GENERIC_ERROR, "fd option is required");
+        return -1;
+    }
+
+    if (fdset_id == -1) {
+        qerror_report(ERROR_CLASS_GENERIC_ERROR, "set option is required");
+        return -1;
+    }
+
+    /* add the fd, and optionally the opaque string, to the fd set */
+    monitor_fdset_add_fd(fd, true, fdset_id, fd_opaque ? true : false,
+                         fd_opaque);
+
+    return 0;
+}
+
 /***********************************************************/
 /* QEMU Block devices */
 
@@ -3299,6 +3326,11 @@ int main(int argc, char **argv, char **envp)
                     exit(0);
                 }
                 break;
+            case QEMU_OPTION_add_fd:
+                opts = qemu_opts_parse(qemu_find_opts("add-fd"), optarg, 0);
+                if (!opts) {
+                    exit(0);
+                }
             default:
                 os_parse_cmd_args(popt->index, optarg);
             }
@@ -3310,6 +3342,10 @@ int main(int argc, char **argv, char **envp)
         exit(1);
     }
 
+    if (qemu_opts_foreach(qemu_find_opts("add-fd"), parse_add_fd, NULL, 1)) {
+        exit(1);
+    }
+
     if (machine == NULL) {
         fprintf(stderr, "No machine found.\n");
         exit(1);
-- 
1.7.11.4