wayland: Factor out the general SHM buffer allocation/free functions from the cursor code

src/video/wayland/SDL_waylandshmbuffer.c

@@ -0,0 +1,172 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+#include "../../SDL_internal.h"
+
+#ifdef SDL_VIDEO_DRIVER_WAYLAND
+
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "SDL_waylandshmbuffer.h"
+#include "SDL_waylandvideo.h"
+
+static int SetTempFileSize(int fd, off_t size)
+{
+#ifdef HAVE_POSIX_FALLOCATE
+    sigset_t set, old_set;
+    int ret;
+
+    /* SIGALRM can potentially block a large posix_fallocate() operation
+     * from succeeding, so block it.
+     */
+    sigemptyset(&set);
+    sigaddset(&set, SIGALRM);
+    sigprocmask(SIG_BLOCK, &set, &old_set);
+
+    do {
+        ret = posix_fallocate(fd, 0, size);
+    } while (ret == EINTR);
+
+    sigprocmask(SIG_SETMASK, &old_set, NULL);
+
+    if (ret == 0) {
+        return 0;
+    } else if (ret != EINVAL && errno != EOPNOTSUPP) {
+        return -1;
+    }
+#endif
+
+    if (ftruncate(fd, size) < 0) {
+        return -1;
+    }
+    return 0;
+}
+
+static int CreateTempFD(off_t size)
+{
+    int fd;
+
+#ifdef HAVE_MEMFD_CREATE
+    fd = memfd_create("SDL", MFD_CLOEXEC | MFD_ALLOW_SEALING);
+    if (fd >= 0) {
+        fcntl(fd, F_ADD_SEALS, F_SEAL_SHRINK | F_SEAL_SEAL);
+    } else
+#endif
+    {
+        static const char template[] = "/sdl-shared-XXXXXX";
+        char *xdg_path;
+        char tmp_path[PATH_MAX];
+
+        xdg_path = SDL_getenv("XDG_RUNTIME_DIR");
+        if (!xdg_path) {
+            return -1;
+        }
+
+        SDL_strlcpy(tmp_path, xdg_path, PATH_MAX);
+        SDL_strlcat(tmp_path, template, PATH_MAX);
+
+        fd = mkostemp(tmp_path, O_CLOEXEC);
+        if (fd < 0) {
+            return -1;
+        }
+
+        /* Need to manually unlink the temp files, or they can persist after close and fill up the temp storage. */
+        unlink(tmp_path);
+    }
+
+    if (SetTempFileSize(fd, size) < 0) {
+        close(fd);
+        return -1;
+    }
+
+    return fd;
+}
+
+static void buffer_handle_release(void *data, struct wl_buffer *wl_buffer)
+{
+    /* NOP */
+}
+
+static struct wl_buffer_listener buffer_listener = {
+    buffer_handle_release
+};
+
+int Wayland_AllocSHMBuffer(int width, int height, struct Wayland_SHMBuffer *shmBuffer)
+{
+    SDL_VideoDevice *vd = SDL_GetVideoDevice();
+    SDL_VideoData *data = vd->driverdata;
+    struct wl_shm_pool *shm_pool;
+    int shm_fd;
+    int stride;
+    const Uint32 SHM_FMT = WL_SHM_FORMAT_ARGB8888;
+
+    if (!shmBuffer) {
+        return SDL_InvalidParamError("shmBuffer");
+    }
+
+    stride = width * 4;
+    shmBuffer->shm_data_size = stride * height;
+
+    shm_fd = CreateTempFD(shmBuffer->shm_data_size);
+    if (shm_fd < 0) {
+        return SDL_SetError("Creating SHM buffer failed.");
+    }
+
+    shmBuffer->shm_data = mmap(NULL, shmBuffer->shm_data_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
+    if (shmBuffer->shm_data == MAP_FAILED) {
+        shmBuffer->shm_data = NULL;
+        close(shm_fd);
+        return SDL_SetError("mmap() failed.");
+    }
+
+    SDL_assert(shmBuffer->shm_data != NULL);
+
+    shm_pool = wl_shm_create_pool(data->shm, shm_fd, shmBuffer->shm_data_size);
+    shmBuffer->wl_buffer = wl_shm_pool_create_buffer(shm_pool, 0, width, height, stride, SHM_FMT);
+    wl_buffer_add_listener(shmBuffer->wl_buffer, &buffer_listener, shmBuffer);
+
+    wl_shm_pool_destroy(shm_pool);
+    close(shm_fd);
+
+    return 0;
+}
+
+void Wayland_ReleaseSHMBuffer(struct Wayland_SHMBuffer *shmBuffer)
+{
+    if (shmBuffer) {
+        if (shmBuffer->wl_buffer) {
+            wl_buffer_destroy(shmBuffer->wl_buffer);
+            shmBuffer->wl_buffer = NULL;
+        }
+        if (shmBuffer->shm_data) {
+            munmap(shmBuffer->shm_data, shmBuffer->shm_data_size);
+            shmBuffer->shm_data = NULL;
+        }
+        shmBuffer->shm_data_size = 0;
+    }
+}
+
+#endif

src/video/wayland/SDL_waylandshmbuffer.h

@@ -0,0 +1,34 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2024 Sam Lantinga <slouken@libsdl.org>
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+#include "../../SDL_internal.h"
+
+#ifndef SDL_waylandshmbuffer_h_
+#define SDL_waylandshmbuffer_h_
+
+struct Wayland_SHMBuffer
+{
+    struct wl_buffer *wl_buffer;
+    void *shm_data;
+    int shm_data_size;
+};
+
+/* Allocates an SHM buffer with the format WL_SHM_FORMAT_ARGB8888 */
+extern int Wayland_AllocSHMBuffer(int width, int height, struct Wayland_SHMBuffer *shmBuffer);
+extern void Wayland_ReleaseSHMBuffer(struct Wayland_SHMBuffer *shmBuffer);
+
+#endif