commit b74cb8761c68275240af0826086590a03a1f419d
author Octavian Purdila <tavip@google.com> Mon Aug 05 18:07:35 2024 -0700
committer Marc-André Lureau <marcandre.lureau@redhat.com> Wed Oct 09 12:13:05 2024 +0400
tree 53584e9b6ea344e182437ac054009acb98fea33f
parent c8e2b6b4d7e2abaf34afd120eb065227ce240106

chardev: add path option for pty backend

Add path option to the pty char backend which will create a symbolic
link to the given path that points to the allocated PTY.

This avoids having to make QMP or HMP monitor queries to find out what
the new PTY device path is.

Based on patch from Paulo Neves:

https://patchew.org/QEMU/1548509635-15776-1-git-send-email-ptsneves@gmail.com/

Tested with the following invocations that the link is created and
removed when qemu stops:

  qemu-system-x86_64 -nodefaults -mon chardev=compat_monitor \
  -chardev pty,path=test,id=compat_monitor0

  qemu-system-x86_64 -nodefaults -monitor pty:test

  # check QMP invocation with path set
  qemu-system-x86_64 -nodefaults -qmp tcp:localhost:4444,server=on,wait=off
  nc localhost 4444
  > {"execute": "qmp_capabilities"}
  > {"execute": "chardev-add", "arguments": {"id": "bar", "backend": {
      "type": "pty", "data": {"path": "test" }}}}

  # check QMP invocation with path not set
  qemu-system-x86_64 -nodefaults -qmp tcp:localhost:4444,server=on,wait=off
  nc localhost 4444
  > {"execute": "qmp_capabilities"}
  > {"execute": "chardev-add", "arguments": {"id": "bar", "backend": {
      "type": "pty", "data": {}}}}

Also tested that when a link path is not passed invocations still work, e.g.:

  qemu-system-x86_64 -monitor pty

Co-authored-by: Paulo Neves <ptsneves@gmail.com>
Signed-off-by: Paulo Neves <ptsneves@gmail.com>
[OP: rebase and address original patch review comments]
Signed-off-by: Octavian Purdila <tavip@google.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-ID: <20240806010735.2450555-1-tavip@google.com>

chardev/char-pty.c

diff --git a/chardev/char-pty.c b/chardev/char-pty.c
index cc2f761..cbb21b7 100644
--- a/chardev/char-pty.c
+++ b/chardev/char-pty.c
@@ -29,6 +29,7 @@
 #include "qemu/sockets.h"
 #include "qemu/error-report.h"
 #include "qemu/module.h"
+#include "qemu/option.h"
 #include "qemu/qemu-print.h"
 
 #include "chardev/char-io.h"
@@ -41,6 +42,7 @@
 
     int connected;
     GSource *timer_src;
+    char *path;
 };
 typedef struct PtyChardev PtyChardev;
 
@@ -204,6 +206,12 @@
     Chardev *chr = CHARDEV(obj);
     PtyChardev *s = PTY_CHARDEV(obj);
 
+    /* unlink symlink */
+    if (s->path) {
+        unlink(s->path);
+        g_free(s->path);
+    }
+
     pty_chr_state(chr, 0);
     object_unref(OBJECT(s->ioc));
     pty_chr_timer_cancel(s);
@@ -330,6 +338,7 @@
     int master_fd, slave_fd;
     char pty_name[PATH_MAX];
     char *name;
+    char *path = backend->u.pty.data->path;
 
     master_fd = qemu_openpty_raw(&slave_fd, pty_name);
     if (master_fd < 0) {
@@ -354,12 +363,36 @@
     g_free(name);
     s->timer_src = NULL;
     *be_opened = false;
+
+    /* create symbolic link */
+    if (path) {
+        int res = symlink(pty_name, path);
+
+        if (res != 0) {
+            error_setg_errno(errp, errno, "Failed to create PTY symlink");
+        } else {
+            s->path = g_strdup(path);
+        }
+    }
+}
+
+static void char_pty_parse(QemuOpts *opts, ChardevBackend *backend,
+                           Error **errp)
+{
+    const char *path = qemu_opt_get(opts, "path");
+    ChardevPty *pty;
+
+    backend->type = CHARDEV_BACKEND_KIND_PTY;
+    pty = backend->u.pty.data = g_new0(ChardevPty, 1);
+    qemu_chr_parse_common(opts, qapi_ChardevPty_base(pty));
+    pty->path = g_strdup(path);
 }
 
 static void char_pty_class_init(ObjectClass *oc, void *data)
 {
     ChardevClass *cc = CHARDEV_CLASS(oc);
 
+    cc->parse = char_pty_parse;
     cc->open = char_pty_open;
     cc->chr_write = char_pty_chr_write;
     cc->chr_update_read_handler = pty_chr_update_read_handler;