asyncio: Added Linux io_uring support.

CMakeLists.txt

···
 set_option(SDL_LIBICONV            "Prefer iconv() from libiconv, if available, over libc version" OFF)
 set_option(SDL_GCC_ATOMICS         "Use gcc builtin atomics" ${SDL_GCC_ATOMICS_DEFAULT})
 dep_option(SDL_DBUS                "Enable D-Bus support" ON "${UNIX_SYS}" OFF)
+dep_option(SDL_LIBURING            "Enable liburing support" ON "${UNIX_SYS}" OFF)
 dep_option(SDL_DISKAUDIO           "Support the disk writer audio driver" ON "SDL_AUDIO" OFF)
 dep_option(SDL_DUMMYAUDIO          "Support the dummy audio driver" ON "SDL_AUDIO" OFF)
 dep_option(SDL_DUMMYVIDEO          "Use dummy video driver" ON "SDL_VIDEO" OFF)
···
         set(SDL_USE_IME 1)
       endif()
 
+      if(SDL_LIBURING)
+        pkg_search_module(LIBURING liburing-ffi)
+        find_path(HAVE_LIBURING_H NAMES liburing.h)
+        if(LIBURING_FOUND AND HAVE_LIBURING_H)
+          set(HAVE_LIBURING_LIBURING_H TRUE)
+          sdl_include_directories(PRIVATE SYSTEM ${LIBURING_INCLUDE_DIRS})
+          set(HAVE_LIBURING TRUE)
+        endif()
+      endif()
+
       if((FREEBSD OR NETBSD) AND NOT HAVE_INOTIFY)
         set(LibInotify_PKG_CONFIG_SPEC libinotify)
         pkg_check_modules(PC_LIBINOTIFY IMPORTED_TARGET ${LibInotify_PKG_CONFIG_SPEC})
···
           sdl_include_directories(PRIVATE SYSTEM ${DXVK_NATIVE_INCLUDE_DIRS})
         endif()
       endif()
+    endif()
+
+    if(HAVE_LIBURING_H)
+      sdl_sources("${SDL3_SOURCE_DIR}/src/file/io_uring/SDL_asyncio_liburing.c")
     endif()
 
     # Always compiled for Linux, unconditionally:

docs/README-linux.md

···
     libxkbcommon-dev libdrm-dev libgbm-dev libgl1-mesa-dev libgles2-mesa-dev \
     libegl1-mesa-dev libdbus-1-dev libibus-1.0-dev libudev-dev fcitx-libs-dev
 
-Ubuntu 22.04+ can also add `libpipewire-0.3-dev libwayland-dev libdecor-0-dev` to that command line.
+Ubuntu 22.04+ can also add `libpipewire-0.3-dev libwayland-dev libdecor-0-dev liburing-dev` to that command line.
 
 Fedora 35, all available features enabled:
 
···
     mesa-libEGL-devel vulkan-devel wayland-devel wayland-protocols-devel \
     libdrm-devel mesa-libgbm-devel libusb-devel libdecor-devel \
     pipewire-jack-audio-connection-kit-devel \
+
+Fedora 39+ can also add `liburing-devel` to that command line.
 
 NOTES:
 - The sndio audio target is unavailable on Fedora (but probably not what you

include/build_config/SDL_build_config.h.cmake

···
 #cmakedefine HAVE_LINUX_INPUT_H 1
 #cmakedefine HAVE_LIBUDEV_H 1
 #cmakedefine HAVE_LIBDECOR_H 1
+#cmakedefine HAVE_LIBURING_H 1
 
 #cmakedefine HAVE_D3D11_H @HAVE_D3D11_H@
 #cmakedefine HAVE_DDRAW_H @HAVE_DDRAW_H@

src/file/SDL_sysasyncio.h

···
 // is #defined to 0 instead and implement the SDL_SYS_* functions below in your
 // backend (having them maybe call into the SDL_SYS_*_Generic versions as a
 // fallback if the platform has functionality that isn't always available).
+#ifdef HAVE_LIBURING_H
+#define SDL_ASYNCIO_ONLY_HAVE_GENERIC 0
+#else
 #define SDL_ASYNCIO_ONLY_HAVE_GENERIC 1
+#endif
 
 // this entire thing is just juggling doubly-linked lists, so make some helper macros.
 #define LINKED_LIST_DECLARE_FIELDS(type, prefix) \

src/file/io_uring/SDL_asyncio_liburing.c

···
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2024 Sam Lantinga <[e-mail]>
+
+  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.
+*/
+
+// The Linux backend uses io_uring for asynchronous i/o, and falls back to
+// the "generic" threadpool implementation if liburing isn't available or
+// fails for some other reason.
+
+#include "SDL_internal.h"
+
+#ifdef HAVE_LIBURING_H
+
+#include "../SDL_sysasyncio.h"
+
+#include <liburing.h>
+#include <errno.h>
+#include <string.h>  // for strerror()
+
+static SDL_InitState liburing_init;
+
+// We could add a whole bootstrap thing like the audio/video/etc subsystems use, but let's keep this simple for now.
+static bool (*CreateAsyncIOQueue)(SDL_AsyncIOQueue *queue);
+static void (*QuitAsyncIO)(void);
+static bool (*AsyncIOFromFile)(const char *file, const char *mode, SDL_AsyncIO *asyncio);
+
+// we never link directly to liburing.
+// (this says "-ffi" which sounds like a scripting language binding thing, but the non-ffi version
+// is static-inline code we can't lookup with dlsym. This is by design.)
+static const char *liburing_library = "liburing-ffi.so.2";
+static void *liburing_handle = NULL;
+
+#define SDL_LIBURING_FUNCS \
+    SDL_LIBURING_FUNC(int, io_uring_queue_init, (unsigned entries, struct io_uring *ring, unsigned flags)) \
+    SDL_LIBURING_FUNC(struct io_uring_probe *,io_uring_get_probe,(void)) \
+    SDL_LIBURING_FUNC(void, io_uring_free_probe, (struct io_uring_probe *probe)) \
+    SDL_LIBURING_FUNC(int, io_uring_opcode_supported, (const struct io_uring_probe *p, int op)) \
+    SDL_LIBURING_FUNC(struct io_uring_sqe *, io_uring_get_sqe, (struct io_uring *ring)) \
+    SDL_LIBURING_FUNC(void, io_uring_prep_read,(struct io_uring_sqe *sqe, int fd, void *buf, unsigned nbytes, __u64 offset)) \
+    SDL_LIBURING_FUNC(void, io_uring_prep_write,(struct io_uring_sqe *sqe, int fd, const void *buf, unsigned nbytes, __u64 offset)) \
+    SDL_LIBURING_FUNC(void, io_uring_prep_close, (struct io_uring_sqe *sqe, int fd)) \
+    SDL_LIBURING_FUNC(void, io_uring_prep_fsync, (struct io_uring_sqe *sqe, int fd, unsigned fsync_flags)) \
+    SDL_LIBURING_FUNC(void, io_uring_prep_cancel, (struct io_uring_sqe *sqe, void *user_data, int flags)) \
+    SDL_LIBURING_FUNC(void, io_uring_prep_timeout, (struct io_uring_sqe *sqe, struct __kernel_timespec *ts, unsigned count, unsigned flags)) \
+    SDL_LIBURING_FUNC(void, io_uring_sqe_set_data, (struct io_uring_sqe *sqe, void *data)) \
+    SDL_LIBURING_FUNC(void, io_uring_sqe_set_flags, (struct io_uring_sqe *sqe, unsigned flags)) \
+    SDL_LIBURING_FUNC(int, io_uring_submit, (struct io_uring *ring)) \
+    SDL_LIBURING_FUNC(int, io_uring_peek_cqe, (struct io_uring *ring, struct io_uring_cqe **cqe_ptr)) \
+    SDL_LIBURING_FUNC(int, io_uring_wait_cqe, (struct io_uring *ring, struct io_uring_cqe **cqe_ptr)) \
+    SDL_LIBURING_FUNC(int, io_uring_wait_cqe_timeout, (struct io_uring *ring, struct io_uring_cqe **cqe_ptr, struct __kernel_timespec *ts)) \
+    SDL_LIBURING_FUNC(void, io_uring_cqe_seen, (struct io_uring *ring, struct io_uring_cqe *cqe)) \
+    SDL_LIBURING_FUNC(void, io_uring_queue_exit, (struct io_uring *ring)) \
+
+
+#define SDL_LIBURING_FUNC(ret, fn, args) typedef ret (*SDL_fntype_##fn) args;
+SDL_LIBURING_FUNCS
+#undef SDL_LIBURING_FUNC
+
+typedef struct SDL_LibUringFunctions
+{
+    #define SDL_LIBURING_FUNC(ret, fn, args) SDL_fntype_##fn fn;
+    SDL_LIBURING_FUNCS
+    #undef SDL_LIBURING_FUNC
+} SDL_LibUringFunctions;
+
+static SDL_LibUringFunctions liburing;
+
+
+typedef struct LibUringAsyncIOQueueData
+{
+    SDL_Mutex *sqe_lock;
+    SDL_Mutex *cqe_lock;
+    struct io_uring ring;
+    SDL_AtomicInt num_waiting;
+} LibUringAsyncIOQueueData;
+
+
+static void UnloadLibUringLibrary(void)
+{
+    if (liburing_library) {
+        SDL_UnloadObject(liburing_handle);
+        liburing_library = NULL;
+    }
+    SDL_zero(liburing);
+}
+
+static bool LoadLibUringSyms(void)
+{
+    #define SDL_LIBURING_FUNC(ret, fn, args) { \
+        liburing.fn = (SDL_fntype_##fn) SDL_LoadFunction(liburing_handle, #fn); \
+        if (!liburing.fn) { \
+            return false; \
+        } \
+    }
+    SDL_LIBURING_FUNCS
+    #undef SDL_LIBURING_FUNC
+    return true;
+}
+
+// we rely on the presence of liburing to handle io_uring for us. The alternative is making
+// direct syscalls into the kernel, which is undesirable. liburing both shields us from this,
+// but also smooths over some kernel version differences, etc.
+static bool LoadLibUring(void)
+{
+    bool result = true;
+
+    if (!liburing_handle) {
+        liburing_handle = SDL_LoadObject(liburing_library);
+        if (!liburing_handle) {
+            result = false;
+            // Don't call SDL_SetError(): SDL_LoadObject already did.
+        } else {
+            result = LoadLibUringSyms();
+            if (result) {
+                static const int needed_ops[] = {
+                    IORING_OP_FSYNC,
+                    IORING_OP_TIMEOUT,
+                    IORING_OP_CLOSE,
+                    IORING_OP_READ,
+                    IORING_OP_WRITE,
+                    IORING_OP_ASYNC_CANCEL
+                };
+
+                struct io_uring_probe *probe = liburing.io_uring_get_probe();
+                if (!probe) {
+                    result = false;
+                } else {
+                    for (int i = 0; i < SDL_arraysize(needed_ops); i++) {
+                        if (!io_uring_opcode_supported(probe, needed_ops[i])) {
+                            result = false;
+                            break;
+                        }
+                    }
+                    liburing.io_uring_free_probe(probe);
+                }
+            }
+
+            if (!result) {
+                UnloadLibUringLibrary();
+            }
+        }
+    }
+    return result;
+}
+
+static bool liburing_SetError(const char *what, int err)
+{
+    SDL_assert(err <= 0);
+    return SDL_SetError("%s failed: %s", what, strerror(-err));
+}
+
+static Sint64 liburing_asyncio_size(void *userdata)
+{
+    const int fd = (int) (size_t) userdata;
+    struct stat statbuf;
+    if (fstat(fd, &statbuf) < 0) {
+        SDL_SetError("fstat failed: %s", strerror(errno));
+        return -1;
+    }
+    return ((Sint64) statbuf.st_size);
+}
+
+// you must hold sqe_lock when calling this!
+static bool liburing_asyncioqueue_queue_task(void *userdata, SDL_AsyncIOTask *task)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) userdata;
+    const int rc = liburing.io_uring_submit(&queuedata->ring);
+    return (rc < 0) ? liburing_SetError("io_uring_submit", rc) : true;
+}
+
+static void liburing_asyncioqueue_cancel_task(void *userdata, SDL_AsyncIOTask *task)
+{
+    SDL_AsyncIOTask *cancel_task = (SDL_AsyncIOTask *) SDL_calloc(1, sizeof (*cancel_task));
+    if (!cancel_task) {
+        return;  // oh well, the task can just finish on its own.
+    }
+
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) userdata;
+    struct io_uring_sqe *sqe = liburing.io_uring_get_sqe(&queuedata->ring);
+    if (!sqe) {
+        SDL_free(cancel_task);
+        return;  // oh well, the task can just finish on its own.
+    }
+
+    cancel_task->app_userdata = task;
+    liburing.io_uring_prep_cancel(sqe, task, 0);
+    liburing.io_uring_sqe_set_data(sqe, cancel_task);
+    liburing_asyncioqueue_queue_task(userdata, task);
+}
+
+static SDL_AsyncIOTask *ProcessCQE(LibUringAsyncIOQueueData *queuedata, struct io_uring_cqe *cqe)
+{
+    if (!cqe) {
+        return NULL;
+    }
+
+    SDL_AsyncIOTask *task = (SDL_AsyncIOTask *) io_uring_cqe_get_data(cqe);
+    if (task) {  // can be NULL if this was just a wakeup message, etc.
+        if (!task->queue) {  // We leave `queue` blank to signify this was a task cancellation.
+            SDL_AsyncIOTask *cancel_task = task;
+            task = (SDL_AsyncIOTask *) cancel_task->app_userdata;
+            SDL_free(cancel_task);
+            if (cqe->res >= 0) {  // cancel was successful?
+                task->result = SDL_ASYNCIO_CANCELLED;
+            } else {
+                task = NULL; // it already finished or was too far along to cancel, so we'll pick up the actual results later.
+            }
+        } else if (cqe->res < 0) {
+            task->result = SDL_ASYNCIO_FAILURE;
+            // !!! FIXME: fill in task->error.
+        } else {
+            if ((task->type == SDL_ASYNCIO_TASK_WRITE) && (((Uint64) cqe->res) < task->requested_size)) {
+                task->result = SDL_ASYNCIO_FAILURE;  // it's always a failure on short writes.
+            } else {
+                task->result = SDL_ASYNCIO_COMPLETE;
+            }
+            if ((task->type == SDL_ASYNCIO_TASK_READ) || (task->type == SDL_ASYNCIO_TASK_WRITE)) {
+                task->result_size = (Uint64) cqe->res;
+            }
+        }
+    }
+
+    return task;
+}
+
+static SDL_AsyncIOTask *liburing_asyncioqueue_get_results(void *userdata)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) userdata;
+
+    // have to hold a lock because otherwise two threads will get the same cqe until we mark it "seen". Copy and mark it right away, then process further.
+    SDL_LockMutex(queuedata->cqe_lock);
+    struct io_uring_cqe *cqe = NULL;
+    const int rc = liburing.io_uring_peek_cqe(&queuedata->ring, &cqe);
+    if (rc != 0) {
+        SDL_assert(rc == -EAGAIN);  // should only fail because nothing is available at the moment.
+        SDL_UnlockMutex(queuedata->cqe_lock);
+        return NULL;
+    }
+    struct io_uring_cqe cqe_copy;
+    SDL_copyp(&cqe_copy, cqe);  // this is only a few bytes.
+    liburing.io_uring_cqe_seen(&queuedata->ring, cqe);  // let io_uring use this slot again.
+    SDL_UnlockMutex(queuedata->cqe_lock);
+
+    return ProcessCQE(queuedata, &cqe_copy);
+}
+
+static SDL_AsyncIOTask *liburing_asyncioqueue_wait_results(void *userdata, Sint32 timeoutMS)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) userdata;
+    struct io_uring_cqe *cqe = NULL;
+
+    SDL_AddAtomicInt(&queuedata->num_waiting, 1);
+    if (timeoutMS < 0) {
+        liburing.io_uring_wait_cqe(&queuedata->ring, &cqe);
+    } else {
+        struct __kernel_timespec ts = { (__kernel_time64_t) timeoutMS / SDL_MS_PER_SECOND, (long long) SDL_MS_TO_NS(timeoutMS % SDL_MS_PER_SECOND) };
+        liburing.io_uring_wait_cqe_timeout(&queuedata->ring, &cqe, &ts);
+    }
+    SDL_AddAtomicInt(&queuedata->num_waiting, -1);
+
+    // (we don't care if the wait failed for any reason, as the upcoming peek_cqe will report valid information. We just wanted the wait operation to block.)
+
+    // each thing that peeks or waits for a completion _gets the same cqe_ until we mark it as seen. So when we wake up from the wait, lock the mutex and
+    // then use peek to make sure we have a unique cqe, and other competing threads either get their own or nothing.
+    return liburing_asyncioqueue_get_results(userdata);  // this just happens to do all those things.
+}
+
+static void liburing_asyncioqueue_signal(void *userdata)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) userdata;
+    const int num_waiting = SDL_GetAtomicInt(&queuedata->num_waiting);
+
+    SDL_LockMutex(queuedata->sqe_lock);
+    for (int i = 0; i < num_waiting; i++) {  // !!! FIXME: is there a better way to do this than pushing a zero-timeout request for everything waiting?
+        struct io_uring_sqe *sqe = liburing.io_uring_get_sqe(&queuedata->ring);
+        if (sqe) {
+            static struct __kernel_timespec ts;   // no wait, just wake a thread as fast as this can land in the completion queue.
+            liburing.io_uring_prep_timeout(sqe, &ts, 0, 0);
+            liburing.io_uring_sqe_set_data(sqe, NULL);
+        }
+    }
+    liburing.io_uring_submit(&queuedata->ring);
+
+    SDL_UnlockMutex(queuedata->sqe_lock);
+}
+
+static void liburing_asyncioqueue_destroy(void *userdata)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) userdata;
+    liburing.io_uring_queue_exit(&queuedata->ring);
+    SDL_DestroyMutex(queuedata->sqe_lock);
+    SDL_DestroyMutex(queuedata->cqe_lock);
+    SDL_free(queuedata);
+}
+
+static bool SDL_SYS_CreateAsyncIOQueue_liburing(SDL_AsyncIOQueue *queue)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) SDL_calloc(1, sizeof (*queuedata));
+    if (!queuedata) {
+        return false;
+    }
+
+    SDL_SetAtomicInt(&queuedata->num_waiting, 0);
+
+    queuedata->sqe_lock = SDL_CreateMutex();
+    if (!queuedata->sqe_lock) {
+        SDL_free(queuedata);
+        return false;
+    }
+
+    queuedata->cqe_lock = SDL_CreateMutex();
+    if (!queuedata->cqe_lock) {
+        SDL_DestroyMutex(queuedata->sqe_lock);
+        SDL_free(queuedata);
+        return false;
+    }
+
+    // !!! FIXME: no idea how large the queue should be. Is 128 overkill or too small?
+    const int rc = liburing.io_uring_queue_init(128, &queuedata->ring, 0);
+    if (rc != 0) {
+        SDL_DestroyMutex(queuedata->sqe_lock);
+        SDL_DestroyMutex(queuedata->cqe_lock);
+        SDL_free(queuedata);
+        return liburing_SetError("io_uring_queue_init", rc);
+    }
+
+    static const SDL_AsyncIOQueueInterface SDL_AsyncIOQueue_liburing = {
+        liburing_asyncioqueue_queue_task,
+        liburing_asyncioqueue_cancel_task,
+        liburing_asyncioqueue_get_results,
+        liburing_asyncioqueue_wait_results,
+        liburing_asyncioqueue_signal,
+        liburing_asyncioqueue_destroy
+    };
+
+    SDL_copyp(&queue->iface, &SDL_AsyncIOQueue_liburing);
+    queue->userdata = queuedata;
+    return true;
+}
+
+
+static bool liburing_asyncio_read(void *userdata, SDL_AsyncIOTask *task)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) task->queue->userdata;
+
+    // !!! FIXME: `unsigned` is likely smaller than requested_size's Uint64. If we overflow it, we could try submitting multiple SQEs
+    // !!! FIXME:  and make a note in the task that there are several in sequence.
+    if (task->requested_size > ((Uint64) ~((unsigned) 0))) {
+        return SDL_SetError("io_uring: i/o task is too large");
+    }
+
+    // have to hold a lock because otherwise two threads could get_sqe and submit while one request isn't fully set up.
+    SDL_LockMutex(queuedata->sqe_lock);
+    struct io_uring_sqe *sqe = liburing.io_uring_get_sqe(&queuedata->ring);
+    if (!sqe) {
+        return SDL_SetError("io_uring: submission queue is full");
+    }
+
+    liburing.io_uring_prep_read(sqe, (int) (size_t) userdata, task->buffer, (unsigned) task->requested_size, task->offset);
+    liburing.io_uring_sqe_set_data(sqe, task);
+
+    const bool retval = task->queue->iface.queue_task(task->queue->userdata, task);
+    SDL_UnlockMutex(queuedata->sqe_lock);
+    return retval;
+}
+
+static bool liburing_asyncio_write(void *userdata, SDL_AsyncIOTask *task)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) task->queue->userdata;
+
+    // !!! FIXME: `unsigned` is likely smaller than requested_size's Uint64. If we overflow it, we could try submitting multiple SQEs
+    // !!! FIXME:  and make a note in the task that there are several in sequence.
+    if (task->requested_size > ((Uint64) ~((unsigned) 0))) {
+        return SDL_SetError("io_uring: i/o task is too large");
+    }
+
+    // have to hold a lock because otherwise two threads could get_sqe and submit while one request isn't fully set up.
+    SDL_LockMutex(queuedata->sqe_lock);
+    struct io_uring_sqe *sqe = liburing.io_uring_get_sqe(&queuedata->ring);
+    if (!sqe) {
+        return SDL_SetError("io_uring: submission queue is full");
+    }
+
+    liburing.io_uring_prep_write(sqe, (int) (size_t) userdata, task->buffer, (unsigned) task->requested_size, task->offset);
+    liburing.io_uring_sqe_set_data(sqe, task);
+
+    const bool retval = task->queue->iface.queue_task(task->queue->userdata, task);
+    SDL_UnlockMutex(queuedata->sqe_lock);
+    return retval;
+}
+
+static bool liburing_asyncio_close(void *userdata, SDL_AsyncIOTask *task)
+{
+    LibUringAsyncIOQueueData *queuedata = (LibUringAsyncIOQueueData *) task->queue->userdata;
+
+    // have to hold a lock because otherwise two threads could get_sqe and submit while one request isn't fully set up.
+    SDL_LockMutex(queuedata->sqe_lock);
+    struct io_uring_sqe *sqe = liburing.io_uring_get_sqe(&queuedata->ring);
+    if (!sqe) {
+        return SDL_SetError("io_uring: submission queue is full");
+    }
+
+    liburing.io_uring_prep_close(sqe, (int) (size_t) userdata);
+    liburing.io_uring_sqe_set_data(sqe, task);
+
+    const bool retval = task->queue->iface.queue_task(task->queue->userdata, task);
+    SDL_UnlockMutex(queuedata->sqe_lock);
+    return retval;
+}
+
+static void liburing_asyncio_destroy(void *userdata)
+{
+    // this is only a Unix file descriptor, should have been closed elsewhere.
+}
+
+static int PosixOpenModeFromString(const char *mode)
+{
+    // this is exactly the set of strings that SDL_AsyncIOFromFile promises will work.
+    static const struct { const char *str; int flags; } mappings[] = {
+        { "rb", O_RDONLY },
+        { "wb", O_WRONLY | O_CREAT | O_TRUNC },
+        { "r+b", O_RDWR },
+        { "w+b", O_RDWR | O_CREAT | O_TRUNC }
+    };
+
+    for (int i = 0; i < SDL_arraysize(mappings); i++) {
+        if (SDL_strcmp(mappings[i].str, mode) == 0) {
+            return mappings[i].flags;
+        }
+    }
+
+    SDL_assert(!"Shouldn't have reached this code");
+    return 0;
+}
+
+static bool SDL_SYS_AsyncIOFromFile_liburing(const char *file, const char *mode, SDL_AsyncIO *asyncio)
+{
+    const int fd = open(file, PosixOpenModeFromString(mode), 0644);
+    if (fd == -1) {
+        return SDL_SetError("open failed: %s", strerror(errno));
+    }
+
+    static const SDL_AsyncIOInterface SDL_AsyncIOFile_liburing = {
+        liburing_asyncio_size,
+        liburing_asyncio_read,
+        liburing_asyncio_write,
+        liburing_asyncio_close,
+        liburing_asyncio_destroy
+    };
+
+    SDL_copyp(&asyncio->iface, &SDL_AsyncIOFile_liburing);
+    asyncio->userdata = (void *) (size_t) fd;
+    return true;
+}
+
+static void SDL_SYS_QuitAsyncIO_liburing(void)
+{
+    UnloadLibUringLibrary();
+}
+
+static void MaybeInitializeLibUring(void)
+{
+    if (SDL_ShouldInit(&liburing_init)) {
+        if (LoadLibUring()) {
+            CreateAsyncIOQueue = SDL_SYS_CreateAsyncIOQueue_liburing;
+            QuitAsyncIO = SDL_SYS_QuitAsyncIO_liburing;
+            AsyncIOFromFile = SDL_SYS_AsyncIOFromFile_liburing;
+        } else {  // can't use liburing? Use the "generic" threadpool implementation instead.
+            CreateAsyncIOQueue = SDL_SYS_CreateAsyncIOQueue_Generic;
+            QuitAsyncIO = SDL_SYS_QuitAsyncIO_Generic;
+            AsyncIOFromFile = SDL_SYS_AsyncIOFromFile_Generic;
+        }
+        SDL_SetInitialized(&liburing_init, true);
+    }
+}
+
+bool SDL_SYS_CreateAsyncIOQueue(SDL_AsyncIOQueue *queue)
+{
+    MaybeInitializeLibUring();
+    return CreateAsyncIOQueue(queue);
+}
+
+bool SDL_SYS_AsyncIOFromFile(const char *file, const char *mode, SDL_AsyncIO *asyncio)
+{
+    MaybeInitializeLibUring();
+    return AsyncIOFromFile(file, mode, asyncio);
+}
+
+void SDL_SYS_QuitAsyncIO(void)
+{
+    if (SDL_ShouldQuit(&liburing_init)) {
+        QuitAsyncIO();
+        CreateAsyncIOQueue = NULL;
+        QuitAsyncIO = NULL;
+        AsyncIOFromFile = NULL;
+        SDL_SetInitialized(&liburing_init, false);
+    }
+}
+
+#endif  // defined HAVE_LIBURING_H
+