init

src/x11/x11_display.c

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+/*
+ * Copyright © 2025 Collabora, Ltd.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ */
+#include "x11_display.h"
+
+#include "util/macros.h"
+#include "util/log.h"
+
+#include <stdio.h>
+#include <X11/Xlibint.h>
+
+#ifdef HAVE_SYS_SHM_H
+#include <xcb/shm.h>
+#include <sys/shm.h>
+#endif
+
+bool
+x11_xlib_display_is_thread_safe(Display *dpy)
+{
+   static bool warned = false;
+
+   /* 'lock_fns' is the XLockDisplay function pointer of the X11 display 'dpy'.
+    * It will be NULL if XInitThreads wasn't called.
+    */
+   if (likely(dpy->lock_fns != NULL))
+      return true;
+
+   if (unlikely(!warned)) {
+      fprintf(stderr, "Xlib is not thread-safe.  This should never be the "
+                      "case starting with XLib 1.8.  Either upgrade XLib "
+                      "or call XInitThreads() from your app.\n");
+      warned = true;
+   }
+
+   return false;
+}
+
+#ifdef HAVE_SYS_SHM_H
+bool
+x11_xcb_display_supports_xshm(xcb_connection_t *con)
+{
+   xcb_generic_error_t *error;
+   xcb_query_extension_cookie_t shm_cookie;
+   xcb_query_extension_reply_t *shm_reply;
+   bool has_mit_shm;
+   int shmid;
+   void *shm_addr = (void *) -1;
+   xcb_shm_seg_t shm_seg;
+   bool ret = true;
+
+   shm_cookie = xcb_query_extension(con, 7, "MIT-SHM");
+   shm_reply = xcb_query_extension_reply(con, shm_cookie, NULL);
+
+   has_mit_shm = shm_reply && shm_reply->present;
+   free(shm_reply);
+   if (!has_mit_shm)
+      return false;
+
+   /* Check if we're a remote client by attempting to detach segment 0.
+    * Remote clients will get BadRequest, local clients get BadValue,
+    * since 'info' has an invalid segment name.
+    */
+   if ((error = xcb_request_check(con,
+                                  xcb_shm_detach_checked(con, 0)))) {
+      bool is_remote = error->error_code == BadRequest;
+      free(error);
+      if (is_remote)
+         return false;
+    }
+
+   /* We're a local client. Now verify we can actually attach SHM.
+    * In some container setups, the X server reports MIT-SHM support
+    * but the client lacks permission to attach shared memory.
+    */
+   shmid = shmget(IPC_PRIVATE, 4096, IPC_CREAT | 0600);
+   if (shmid < 0) {
+      mesa_logd("shared memory allocation error: %s", strerror(errno));
+      return false;
+   }
+
+   shm_addr = shmat(shmid, NULL, 0);
+   if (shm_addr == (void *) -1) {
+      mesa_logd("shmat failed: %s", strerror(errno));
+      ret = false;
+      goto check_xshm_cleanup;
+   }
+
+   shm_seg = xcb_generate_id(con);
+   error = xcb_request_check(con,
+                             xcb_shm_attach_checked(con,
+                                                    shm_seg, shmid, 0));
+   if (error) {
+      mesa_logd("Failed to attach to x11 shm with error: %u", error->error_code);
+      free(error);
+      ret = false;
+      goto check_xshm_cleanup;
+   }
+
+   /* Only detach if it was attached successfully */
+   xcb_shm_detach(con, shm_seg);
+
+check_xshm_cleanup:
+   if (shm_addr != (void *) -1)
+      shmdt(shm_addr);
+   shmctl(shmid, IPC_RMID, NULL);
+
+   return ret;
+}
+#endif