[4/8] guest agent: add guest-pipe-open

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index fd746db..bf14518 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -208,9 +208,11 @@  void qmp_guest_set_time(bool has_time, int64_t time_ns, Error **errp)
     }
 }
 
+
 typedef struct GuestFileHandle {
     uint64_t id;
     FILE *fh;
+    int pipe_other_end_fd; /* if set, it's a pipe fd of the other end. */
     QTAILQ_ENTRY(GuestFileHandle) next;
 } GuestFileHandle;
 
@@ -218,7 +220,8 @@  static struct {
     QTAILQ_HEAD(, GuestFileHandle) filehandles;
 } guest_file_state;
 
-static int64_t guest_file_handle_add(FILE *fh, Error **errp)
+static int64_t guest_file_handle_add(FILE *fh, int pipe_other_end_fd,
+                                     Error **errp)
 {
     GuestFileHandle *gfh;
     int64_t handle;
@@ -231,6 +234,7 @@  static int64_t guest_file_handle_add(FILE *fh, Error **errp)
     gfh = g_malloc0(sizeof(GuestFileHandle));
     gfh->id = handle;
     gfh->fh = fh;
+    gfh->pipe_other_end_fd = pipe_other_end_fd;
     QTAILQ_INSERT_TAIL(&guest_file_state.filehandles, gfh, next);
 
     return handle;
@@ -422,7 +426,7 @@  int64_t qmp_guest_file_open(const char *path, bool has_mode, const char *mode,
         return -1;
     }
 
-    handle = guest_file_handle_add(fh, errp);
+    handle = guest_file_handle_add(fh, -1, errp);
     if (handle < 0) {
         fclose(fh);
         return -1;
@@ -432,6 +436,75 @@  int64_t qmp_guest_file_open(const char *path, bool has_mode, const char *mode,
     return handle;
 }
 
+int64_t qmp_guest_pipe_open(const char *mode, Error **err)
+{
+    FILE *f = NULL;
+    int fd[2], this_end, other_end;
+    int64_t handle;
+
+    slog("guest-pipe-open called");
+
+    if ((mode[0] != 'r' && mode[0] != 'w') || mode[1] != '\0') {
+        error_set(err, ERROR_CLASS_GENERIC_ERROR,
+                  "Only \"r\" or \"w\" are the valid modes to open a pipe");
+        return -1;
+    }
+
+    if (pipe(fd) != 0) {
+        error_set_errno(err, errno, QERR_QGA_COMMAND_FAILED, "pipe() failed");
+        return -1;
+    }
+
+    this_end = (mode[0] == 'w');
+    other_end = !this_end;
+
+    if (guest_file_toggle_flags(fd[this_end], O_NONBLOCK, true, err) == -1) {
+        goto fail;
+    }
+
+    qemu_set_cloexec(fd[this_end]);
+    qemu_set_cloexec(fd[other_end]);
+
+    f = fdopen(fd[this_end], mode);
+    if (f == NULL) {
+        error_set_errno(err, errno, QERR_QGA_COMMAND_FAILED,
+                        "fdopen() failed to open pipe handle");
+        goto fail;
+    }
+
+    handle = guest_file_handle_add(f, fd[other_end], err);
+    if (handle == -1) {
+        goto fail;
+    }
+
+    slog("guest-pipe-open: handle: %" PRId64, handle);
+
+    return handle;
+
+fail:
+    if (f != NULL) {
+        fclose(f);
+    } else {
+        close(fd[this_end]);
+    }
+    close(fd[other_end]);
+
+    return -1;
+}
+
+static int guest_pipe_close_other_end(GuestFileHandle *gfh)
+{
+    if (gfh->pipe_other_end_fd != -1) {
+        if (close(gfh->pipe_other_end_fd) != 0) {
+            return 1;
+        }
+
+        gfh->pipe_other_end_fd = -1;
+    }
+
+    return 0;
+}
+
 void qmp_guest_file_close(int64_t handle, Error **errp)
 {
     GuestFileHandle *gfh = guest_file_handle_find(handle, errp);
@@ -442,6 +515,11 @@  void qmp_guest_file_close(int64_t handle, Error **errp)
         return;
     }
 
+    if (guest_pipe_close_other_end(gfh) != 0) {
+        error_setg_errno(errp, errno, "failed to close pipe handle");
+        return;
+    }
+
     ret = fclose(gfh->fh);
     if (ret == EOF) {
         error_setg_errno(errp, errno, "failed to close handle");
diff --git a/qga/commands-win32.c b/qga/commands-win32.c
index 5db96ef..5cb7946 100644
--- a/qga/commands-win32.c
+++ b/qga/commands-win32.c
@@ -154,6 +154,12 @@  int64_t qmp_guest_file_open(const char *path, bool has_mode,
     return fd;
 }
 
+int64_t qmp_guest_pipe_open(const char *mode, Error **errp)
+{
+    error_set(errp, QERR_UNSUPPORTED);
+    return 0;
+}
+
 void qmp_guest_file_close(int64_t handle, Error **errp)
 {
     bool ret;
@@ -683,7 +689,7 @@  GList *ga_command_blacklist_init(GList *blacklist)
         "guest-suspend-hybrid", "guest-network-get-interfaces",
         "guest-get-vcpus", "guest-set-vcpus",
         "guest-fsfreeze-freeze-list", "guest-get-fsinfo",
-        "guest-fstrim", NULL};
+        "guest-fstrim", "guest-pipe-open", NULL};
     char **p = (char **)list_unsupported;
 
     while (*p) {
diff --git a/qga/qapi-schema.json b/qga/qapi-schema.json
index 376e79f..67d3b72 100644
--- a/qga/qapi-schema.json
+++ b/qga/qapi-schema.json
@@ -212,12 +212,33 @@ 
   'returns': 'int' }
 
 ##
+# @guest-pipe-open
+#
+# Open a pipe to in the guest to associated with a qga-spawned processes
+# for communication.
+#
+# Returns: Guest file handle on success, as per guest-file-open. This
+# handle is useable with the same interfaces as a handle returned by
+# guest-file-open.
+#
+# Since: 2.3
+##
+{ 'command': 'guest-pipe-open',
+  'data':    { 'mode': 'str' },
+  'returns': 'int' }
+
+##
 # @guest-file-close:
 #
 # Close an open file in the guest
 #
 # @handle: filehandle returned by guest-file-open
 #
+# Please note that closing the write side of a pipe will block until the read
+# side is closed.  If you passed the read-side of the pipe to a qga-spawned
+# process, make sure the process has exited before attempting to close the
+# write side.
+#
 # Returns: Nothing on success.
 #
 # Since: 0.15.0