[PATCH 1/2] qmp: Add 'openfd' command

[Dr. David Alan Gilbert (git)]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

The existing 'getfd' command imports an fd from the monitor via
SCM rights.
This command allows qemu to open the file for itself; this is convenient
primarily in testing, or with simple QMP clients.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 monitor/misc.c | 48 ++++++++++++++++++++++++++++++++++++++----------
 qapi/misc.json | 23 ++++++++++++++++++++++-
 2 files changed, 60 insertions(+), 11 deletions(-)

diff --git a/monitor/misc.c b/monitor/misc.c
index f5207cd242..d538af592a 100644
--- a/monitor/misc.c
+++ b/monitor/misc.c
@@ -1230,22 +1230,20 @@ static void hmp_acl_remove(Monitor *mon, const QDict 
*qdict)
     }
 }
 
-void qmp_getfd(const char *fdname, Error **errp)
+/*
+ * Add a named fd to the monitor list.
+ * Returns true on success.
+ */
+static bool addfd(const char *fdname, int fd, Error **errp)
 {
     mon_fd_t *monfd;
-    int fd, tmp_fd;
-
-    fd = qemu_chr_fe_get_msgfd(&cur_mon->chr);
-    if (fd == -1) {
-        error_setg(errp, QERR_FD_NOT_SUPPLIED);
-        return;
-    }
+    int tmp_fd;
 
     if (qemu_isdigit(fdname[0])) {
         close(fd);
         error_setg(errp, QERR_INVALID_PARAMETER_VALUE, "fdname",
                    "a name not starting with a digit");
-        return;
+        return false;
     }
 
     qemu_mutex_lock(&cur_mon->mon_lock);
@@ -1259,7 +1257,7 @@ void qmp_getfd(const char *fdname, Error **errp)
         qemu_mutex_unlock(&cur_mon->mon_lock);
         /* Make sure close() is outside critical section */
         close(tmp_fd);
-        return;
+        return true;
     }
 
     monfd = g_malloc0(sizeof(mon_fd_t));
@@ -1268,6 +1266,36 @@ void qmp_getfd(const char *fdname, Error **errp)
 
     QLIST_INSERT_HEAD(&cur_mon->fds, monfd, next);
     qemu_mutex_unlock(&cur_mon->mon_lock);
+
+    return true;
+}
+
+void qmp_getfd(const char *fdname, Error **errp)
+{
+    int fd = qemu_chr_fe_get_msgfd(&cur_mon->chr);
+    if (fd == -1) {
+        error_setg(errp, QERR_FD_NOT_SUPPLIED);
+        return;
+    }
+
+    if (!addfd(fdname, fd, errp)) {
+        close(fd);
+    }
+}
+
+void qmp_openfd(const char *fdname, const char *filename, Error **errp)
+{
+    int fd;
+
+    fd = open(filename, O_RDWR | O_CREAT, S_IRWXU);
+    if (fd == -1) {
+        error_setg_errno(errp, errno, "Cannot open file '%s'", filename);
+        return;
+    }
+
+    if (!addfd(fdname, fd, errp)) {
+        close(fd);
+    }
 }
 
 void qmp_closefd(const char *fdname, Error **errp)
diff --git a/qapi/misc.json b/qapi/misc.json
index 99b90ac80b..baec07358e 100644
--- a/qapi/misc.json
+++ b/qapi/misc.json
@@ -952,7 +952,7 @@
 ##
 # @closefd:
 #
-# Close a file descriptor previously passed via SCM rights
+# Close a named file descriptor
 #
 # @fdname: file descriptor name
 #
@@ -968,6 +968,27 @@
 ##
 { 'command': 'closefd', 'data': {'fdname': 'str'} }
 
+##
+# @openfd:
+#
+# Open a file descriptor.  The file is opened read-write.
+#
+# @fdname: file descriptor name
+# @filename: file name
+#
+# Returns: Nothing on success
+#
+# Since: 5.1
+#
+# Example:
+#
+# -> { "execute": "openfd", "arguments": { "fdname": "null",
+#                                          "filename": "/dev/null" } }
+# <- { "return": {} }
+#
+##
+{ 'command': 'openfd', 'data': {'fdname': 'str', 'filename': 'str'} }
+
 ##
 # @MemoryInfo:
 #
-- 
2.26.2