Atlas - SDL_waylandshmbuffer.c
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1/*
2  Simple DirectMedia Layer
3  Copyright (C) 1997-2025 Sam Lantinga <[email protected]>
4
5  This software is provided 'as-is', without any express or implied
6  warranty.  In no event will the authors be held liable for any damages
7  arising from the use of this software.
8
9  Permission is granted to anyone to use this software for any purpose,
10  including commercial applications, and to alter it and redistribute it
11  freely, subject to the following restrictions:
12
13  1. The origin of this software must not be misrepresented; you must not
14     claim that you wrote the original software. If you use this software
15     in a product, an acknowledgment in the product documentation would be
16     appreciated but is not required.
17  2. Altered source versions must be plainly marked as such, and must not be
18     misrepresented as being the original software.
19  3. This notice may not be removed or altered from any source distribution.
20*/
21
22#include "SDL_internal.h"
23
24#ifdef SDL_VIDEO_DRIVER_WAYLAND
25
26#include <errno.h>
27#include <fcntl.h>
28#include <limits.h>
29#include <signal.h>
30#include <sys/mman.h>
31#include <unistd.h>
32
33#include "SDL_waylandshmbuffer.h"
34#include "SDL_waylandvideo.h"
35
36static bool SetTempFileSize(int fd, off_t size)
37{
38#ifdef HAVE_POSIX_FALLOCATE
39    sigset_t set, old_set;
40    int ret;
41
42    /* SIGALRM can potentially block a large posix_fallocate() operation
43     * from succeeding, so block it.
44     */
45    sigemptyset(&set);
46    sigaddset(&set, SIGALRM);
47    sigprocmask(SIG_BLOCK, &set, &old_set);
48
49    do {
50        ret = posix_fallocate(fd, 0, size);
51    } while (ret == EINTR);
52
53    sigprocmask(SIG_SETMASK, &old_set, NULL);
54
55    if (ret == 0) {
56        return true;
57    } else if (ret != EINVAL && errno != EOPNOTSUPP) {
58        return false;
59    }
60#endif
61
62    if (ftruncate(fd, size) < 0) {
63        return false;
64    }
65    return true;
66}
67
68static int CreateTempFD(off_t size)
69{
70    int fd;
71
72#ifdef HAVE_MEMFD_CREATE
73    fd = memfd_create("SDL", MFD_CLOEXEC | MFD_ALLOW_SEALING);
74    if (fd >= 0) {
75        fcntl(fd, F_ADD_SEALS, F_SEAL_SHRINK | F_SEAL_SEAL);
76    } else
77#endif
78    {
79        static const char template[] = "/sdl-shared-XXXXXX";
80        const char *xdg_path;
81        char tmp_path[PATH_MAX];
82
83        xdg_path = SDL_getenv("XDG_RUNTIME_DIR");
84        if (!xdg_path) {
85            return -1;
86        }
87
88        SDL_strlcpy(tmp_path, xdg_path, PATH_MAX);
89        SDL_strlcat(tmp_path, template, PATH_MAX);
90
91        fd = mkostemp(tmp_path, O_CLOEXEC);
92        if (fd < 0) {
93            return -1;
94        }
95
96        // Need to manually unlink the temp files, or they can persist after close and fill up the temp storage.
97        unlink(tmp_path);
98    }
99
100    if (!SetTempFileSize(fd, size)) {
101        close(fd);
102        return -1;
103    }
104
105    return fd;
106}
107
108static void buffer_handle_release(void *data, struct wl_buffer *wl_buffer)
109{
110    // NOP
111}
112
113static struct wl_buffer_listener buffer_listener = {
114    buffer_handle_release
115};
116
117struct Wayland_SHMPool
118{
119    struct wl_shm_pool *shm_pool;
120    void *shm_pool_memory;
121    int shm_pool_size;
122    int offset;
123};
124
125Wayland_SHMPool *Wayland_AllocSHMPool(int size)
126{
127    SDL_VideoDevice *vd = SDL_GetVideoDevice();
128    SDL_VideoData *data = vd->internal;
129
130    if (size <= 0) {
131        return NULL;
132    }
133
134    Wayland_SHMPool *shmPool = SDL_calloc(1, sizeof(Wayland_SHMPool));
135    if (!shmPool) {
136        return NULL;
137    }
138
139    shmPool->shm_pool_size = (size + 15) & (~15);
140
141    const int shm_fd = CreateTempFD(shmPool->shm_pool_size);
142    if (shm_fd < 0) {
143        SDL_free(shmPool);
144        SDL_SetError("Creating SHM buffer failed.");
145        return NULL;
146    }
147
148    shmPool->shm_pool_memory = mmap(NULL, shmPool->shm_pool_size, PROT_READ | PROT_WRITE, MAP_SHARED, shm_fd, 0);
149    if (shmPool->shm_pool_memory == MAP_FAILED) {
150        shmPool->shm_pool_memory = NULL;
151        close(shm_fd);
152        SDL_free(shmPool);
153        SDL_SetError("mmap() failed.");
154        return NULL;
155    }
156
157    shmPool->shm_pool = wl_shm_create_pool(data->shm, shm_fd, shmPool->shm_pool_size);
158    close(shm_fd);
159
160    return shmPool;
161}
162
163struct wl_buffer *Wayland_AllocBufferFromPool(Wayland_SHMPool *shmPool, int width, int height, void **data)
164{
165    const Uint32 SHM_FMT = WL_SHM_FORMAT_ARGB8888;
166
167    if (!shmPool || !width || !height || !data) {
168        return NULL;
169    }
170
171    *data = (Uint8 *)shmPool->shm_pool_memory + shmPool->offset;
172    struct wl_buffer *buffer = wl_shm_pool_create_buffer(shmPool->shm_pool, shmPool->offset, width, height, width * 4, SHM_FMT);
173    wl_buffer_add_listener(buffer, &buffer_listener, shmPool);
174
175    shmPool->offset += width * height * 4;
176
177    return buffer;
178}
179
180void Wayland_ReleaseSHMPool(Wayland_SHMPool *shmPool)
181{
182    if (shmPool) {
183        wl_shm_pool_destroy(shmPool->shm_pool);
184        munmap(shmPool->shm_pool_memory, shmPool->shm_pool_size);
185        SDL_free(shmPool);
186    }
187}
188
189#endif
190
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