[v9,2/7] qapi: Introduce add-fd, remove-fd, query-fdsets

diff --git a/monitor.c b/monitor.c
index 49dccfe..c1851f0 100644
--- a/monitor.c
+++ b/monitor.c
@@ -140,6 +140,23 @@  struct mon_fd_t {
     QLIST_ENTRY(mon_fd_t) next;
 };
 
+/* file descriptor associated with a file descriptor set */
+typedef struct MonFdsetFd MonFdsetFd;
+struct MonFdsetFd {
+    int fd;
+    bool removed;
+    char *opaque;
+    QLIST_ENTRY(MonFdsetFd) next;
+};
+
+/* file descriptor set containing fds passed via SCM_RIGHTS */
+typedef struct MonFdset MonFdset;
+struct MonFdset {
+    int64_t id;
+    QLIST_HEAD(, MonFdsetFd) fds;
+    QLIST_ENTRY(MonFdset) next;
+};
+
 typedef struct MonitorControl {
     QObject *id;
     JSONMessageParser parser;
@@ -211,6 +228,7 @@  static inline int mon_print_count_get(const Monitor *mon) { return 0; }
 #define QMP_ACCEPT_UNKNOWNS 1
 
 static QLIST_HEAD(mon_list, Monitor) mon_list;
+static QLIST_HEAD(mon_fdsets, MonFdset) mon_fdsets;
 
 static mon_cmd_t mon_cmds[];
 static mon_cmd_t info_cmds[];
@@ -2389,6 +2407,173 @@  int monitor_get_fd(Monitor *mon, const char *fdname)
     return -1;
 }
 
+static void monitor_fdset_cleanup(MonFdset *mon_fdset)
+{
+    MonFdsetFd *mon_fdset_fd;
+    MonFdsetFd *mon_fdset_fd_next;
+
+    QLIST_FOREACH_SAFE(mon_fdset_fd, &mon_fdset->fds, next, mon_fdset_fd_next) {
+        if (mon_fdset_fd->removed) {
+            close(mon_fdset_fd->fd);
+            g_free(mon_fdset_fd->opaque);
+            QLIST_REMOVE(mon_fdset_fd, next);
+            g_free(mon_fdset_fd);
+        }
+    }
+
+    if (QLIST_EMPTY(&mon_fdset->fds)) {
+        QLIST_REMOVE(mon_fdset, next);
+        g_free(mon_fdset);
+    }
+}
+
+AddfdInfo *qmp_add_fd(bool has_fdset_id, int64_t fdset_id, bool has_opaque,
+                      const char *opaque, Error **errp)
+{
+    int fd;
+    Monitor *mon = cur_mon;
+    MonFdset *mon_fdset;
+    MonFdsetFd *mon_fdset_fd;
+    AddfdInfo *fdinfo;
+
+    fd = qemu_chr_fe_get_msgfd(mon->chr);
+    if (fd == -1) {
+        error_set(errp, QERR_FD_NOT_SUPPLIED);
+        goto error;
+    }
+
+    if (has_fdset_id) {
+        QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
+            if (mon_fdset->id == fdset_id) {
+                break;
+            }
+        }
+        if (mon_fdset == NULL) {
+            error_set(errp, QERR_INVALID_PARAMETER_VALUE, "fdset-id",
+                      "an existing fdset-id or no fdset-id");
+            goto error;
+        }
+    } else {
+        int64_t fdset_id_prev = -1;
+        MonFdset *mon_fdset_cur = QLIST_FIRST(&mon_fdsets);
+
+        /* Use first available fdset ID */
+        QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
+            mon_fdset_cur = mon_fdset;
+            if (fdset_id_prev == mon_fdset_cur->id - 1) {
+                fdset_id_prev = mon_fdset_cur->id;
+                continue;
+            }
+            break;
+        }
+
+        mon_fdset = g_malloc0(sizeof(*mon_fdset));
+        mon_fdset->id = fdset_id_prev + 1;
+
+        /* The fdset list is ordered by fdset ID */
+        if (mon_fdset->id == 0) {
+            QLIST_INSERT_HEAD(&mon_fdsets, mon_fdset, next);
+        } else if (mon_fdset->id < mon_fdset_cur->id) {
+            QLIST_INSERT_BEFORE(mon_fdset_cur, mon_fdset, next);
+        } else {
+            QLIST_INSERT_AFTER(mon_fdset_cur, mon_fdset, next);
+        }
+    }
+
+    mon_fdset_fd = g_malloc0(sizeof(*mon_fdset_fd));
+    mon_fdset_fd->fd = fd;
+    mon_fdset_fd->removed = false;
+    if (has_opaque) {
+        mon_fdset_fd->opaque = g_strdup(opaque);
+    }
+    QLIST_INSERT_HEAD(&mon_fdset->fds, mon_fdset_fd, next);
+
+    fdinfo = g_malloc0(sizeof(*fdinfo));
+    fdinfo->fdset_id = mon_fdset->id;
+    fdinfo->fd = mon_fdset_fd->fd;
+
+    return fdinfo;
+
+error:
+    if (fd != -1) {
+        close(fd);
+    }
+    return NULL;
+}
+
+void qmp_remove_fd(int64_t fdset_id, bool has_fd, int64_t fd, Error **errp)
+{
+    MonFdset *mon_fdset;
+    MonFdsetFd *mon_fdset_fd;
+    char fd_str[60];
+
+    QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
+        if (mon_fdset->id != fdset_id) {
+            continue;
+        }
+        QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
+            if (has_fd) {
+                if (mon_fdset_fd->fd != fd) {
+                    continue;
+                }
+                mon_fdset_fd->removed = true;
+                break;
+            } else {
+                mon_fdset_fd->removed = true;
+            }
+        }
+        if (has_fd && !mon_fdset_fd) {
+            goto error;
+        }
+        monitor_fdset_cleanup(mon_fdset);
+        return;
+    }
+
+error:
+    snprintf(fd_str, sizeof(fd_str),
+             "fdset-id:%" PRId64 ", fd:%" PRId64, fdset_id, fd);
+    error_set(errp, QERR_FD_NOT_FOUND, fd_str);
+}
+
+FdsetInfoList *qmp_query_fdsets(Error **errp)
+{
+    MonFdset *mon_fdset;
+    MonFdsetFd *mon_fdset_fd;
+    FdsetInfoList *fdset_list = NULL;
+
+    QLIST_FOREACH(mon_fdset, &mon_fdsets, next) {
+        FdsetInfoList *fdset_info = g_malloc0(sizeof(*fdset_info));
+        FdsetFdInfoList *fdsetfd_list = NULL;
+
+        fdset_info->value = g_malloc0(sizeof(*fdset_info->value));
+        fdset_info->value->fdset_id = mon_fdset->id;
+
+        QLIST_FOREACH(mon_fdset_fd, &mon_fdset->fds, next) {
+            FdsetFdInfoList *fdsetfd_info;
+
+            fdsetfd_info = g_malloc0(sizeof(*fdsetfd_info));
+            fdsetfd_info->value = g_malloc0(sizeof(*fdsetfd_info->value));
+            fdsetfd_info->value->fd = mon_fdset_fd->fd;
+            if (mon_fdset_fd->opaque) {
+                fdsetfd_info->value->has_opaque = true;
+                fdsetfd_info->value->opaque = g_strdup(mon_fdset_fd->opaque);
+            } else {
+                fdsetfd_info->value->has_opaque = false;
+            }
+
+            fdsetfd_info->next = fdsetfd_list;
+            fdsetfd_list = fdsetfd_info;
+        }
+
+        fdset_info->value->fds = fdsetfd_list;
+
+        fdset_info->next = fdset_list;
+        fdset_list = fdset_info;
+    }
+
+    return fdset_list;
+}
+
 /* mon_cmds and info_cmds would be sorted at runtime */
 static mon_cmd_t mon_cmds[] = {
 #include "hmp-commands.h"
diff --git a/qapi-schema.json b/qapi-schema.json
index bd9c450..53cf083 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -2199,3 +2199,101 @@ 
 # Since: 0.14.0
 ##
 { 'command': 'closefd', 'data': {'fdname': 'str'} }
+
+# @AddfdInfo:
+#
+# Information about a file descriptor that was added to an fd set.
+#
+# @fdset-id: The ID of the fd set that @fd was added to.
+#
+# @fd: The file descriptor that was received via SCM rights and
+#      added to the fd set.
+#
+# Since: 1.2.0
+##
+{ 'type': 'AddfdInfo', 'data': {'fdset-id': 'int', 'fd': 'int'} }
+
+##
+# @add-fd:
+#
+# Add a file descriptor, that was passed via SCM rights, to an fd set.
+#
+# @fdset-id: #optional The ID of the fd set to add the file descriptor to.
+#
+# @opaque: #optional A free-form string that can be used to describe the fd.
+#
+# Returns: @AddfdInfo on success
+#          If file descriptor was not received, FdNotSupplied
+#          If @fdset-id does not exist, InvalidParameterValue
+#
+# Notes: The list of fd sets is shared by all monitor connections.
+#
+#        If @fdset-id is not specified, a new fd set will be created.
+#
+# Since: 1.2.0
+##
+{ 'command': 'add-fd', 'data': {'*fdset-id': 'int', '*opaque': 'str'},
+  'returns': 'AddfdInfo' }
+
+##
+# @remove-fd:
+#
+# Remove a file descriptor from an fd set.
+#
+# @fdset-id: The ID of the fd set that the file descriptor belongs to.
+#
+# @fd: #optional The file descriptor that is to be removed.
+#
+# Returns: Nothing on success
+#          If @fdset-id or @fd is not found, FdNotFound
+#
+# Since: 1.2.0
+#
+# Notes: The list of fd sets is shared by all monitor connections.
+#
+#        If @fd is not specified, all file descriptors in @fdset-id
+#        will be removed.
+##
+{ 'command': 'remove-fd', 'data': {'fdset-id': 'int', '*fd': 'int'} }
+
+##
+# @FdsetFdInfo:
+#
+# Information about a file descriptor that belongs to an fd set.
+#
+# @fd: The file descriptor value.
+#
+# @opaque: #optional A free-form string that can be used to describe the fd.
+#
+# Since: 1.2.0
+##
+{ 'type': 'FdsetFdInfo',
+  'data': {'fd': 'int', '*opaque': 'str'} }
+
+##
+# @FdsetInfo:
+#
+# Information about an fd set.
+#
+# @fdset-id: The ID of the fd set.
+#
+# @fds: A list of file descriptors that belong to this fd set.
+#
+# Since: 1.2.0
+##
+{ 'type': 'FdsetInfo',
+  'data': {'fdset-id': 'int', 'fds': ['FdsetFdInfo']} }
+
+##
+# @query-fdsets:
+#
+# Return information describing all fd sets.
+#
+# Returns: A list of @FdsetInfo
+#
+# Since: 1.2.0
+#
+# Note: The list of fd sets is shared by all monitor connections.
+#
+##
+{ 'command': 'query-fdsets', 'returns': ['FdsetInfo'] }
diff --git a/qmp-commands.hx b/qmp-commands.hx
index ac46638..f44926c 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -926,6 +926,128 @@  Example:
 
 EQMP
 
+     {
+        .name       = "add-fd",
+        .args_type  = "fdset-id:i?,opaque:s?",
+        .params     = "add-fd fdset-id opaque",
+        .help       = "Add a file descriptor, that was passed via SCM rights, to an fd set",
+        .mhandler.cmd_new = qmp_marshal_input_add_fd,
+    },
+
+SQMP
+add-fd
+-------
+
+Add a file descriptor, that was passed via SCM rights, to an fd set.
+
+Arguments:
+
+- "fdset-id": The ID of the fd set to add the file descriptor to.
+              (json-int, optional)
+- "opaque": A free-form string that can be used to describe the fd.
+            (json-string, optional)
+
+Return a json-object with the following information:
+
+- "fdset-id": The ID of the fd set that the fd was added to. (json-int)
+- "fd": The file descriptor that was received via SCM rights and added to the
+        fd set. (json-int)
+
+Example:
+
+-> { "execute": "add-fd", "arguments": { "fdset-id": 1 } }
+<- { "return": { "fdset-id": 1, "fd": 3 } }
+
+Notes:
+
+(1) The list of fd sets is shared by all monitor connections.
+(2) If "fdset-id" is not specified, a new fd set will be created.
+
+EQMP
+
+     {
+        .name       = "remove-fd",
+        .args_type  = "fdset-id:i,fd:i?",
+        .params     = "remove-fd fdset-id fd",
+        .help       = "Remove a file descriptor from an fd set",
+        .mhandler.cmd_new = qmp_marshal_input_remove_fd,
+    },
+
+SQMP
+remove-fd
+---------
+
+Remove a file descriptor from an fd set.
+
+Arguments:
+
+- "fdset-id": The ID of the fd set that the file descriptor belongs to.
+              (json-int)
+- "fd": The file descriptor that is to be removed. (json-int, optional)
+
+Example:
+
+-> { "execute": "remove-fd", "arguments": { "fdset-id": 1, "fd": 3 } }
+<- { "return": {} }
+
+Notes:
+
+(1) The list of fd sets is shared by all monitor connections.
+(2) If "fd" is not specified, all file descriptors in "fdset-id" will be
+    removed.
+
+EQMP
+
+    {
+        .name       = "query-fdsets",
+        .args_type  = "",
+        .help       = "Return information describing all fd sets",
+        .mhandler.cmd_new = qmp_marshal_input_query_fdsets,
+    },
+
+SQMP
+query-fdsets
+-------------
+
+Return information describing all fd sets.
+
+Arguments: None
+
+Example:
+
+-> { "execute": "query-fdsets" }
+<- { "return": [
+       {
+         "fds": [
+           {
+             "fd": 30,
+             "opaque": "rdonly:/path/to/file"
+           },
+           {
+             "fd": 24,
+             "opaque": "rdwr:/path/to/file"
+           }
+         ],
+         "fdset-id": 1
+       },
+       {
+         "fds": [
+           {
+             "fd": 28
+           },
+           {
+             "fd": 29
+           }
+         ],
+         "fdset-id": 0
+       },
+     ]
+   }
+
+Note: The list of fd sets is shared by all monitor connections.
+
+EQMP
+
     {
         .name       = "block_passwd",
         .args_type  = "device:B,password:s",