WasmFS JS API: Implement mmap (#20019)

This PR implements mmap, msync, and munmap, and adds JS API tests to test_fs_js_api.

emcc.py

@@ -2358,6 +2358,7 @@ def phase_linker_setup(options, state, newargs):
       # included, as the entire JS library can refer to things that require
       # these exports.)
       settings.REQUIRED_EXPORTS += [
+        'emscripten_builtin_memalign',
         'wasmfs_create_file',
         '_wasmfs_mount',
         '_wasmfs_unmount',
@@ -2374,6 +2375,9 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_chdir',
         '_wasmfs_mknod',
         '_wasmfs_rmdir',
+        '_wasmfs_mmap',
+        '_wasmfs_munmap',
+        '_wasmfs_msync',
         '_wasmfs_read',
         '_wasmfs_pread',
         '_wasmfs_symlink',

src/library_wasmfs.js

@@ -260,9 +260,19 @@ FS.createPreloadedFile = FS_createPreloadedFile;
     allocate(stream, offset, length) {
       return FS.handleError(__wasmfs_allocate(stream.fd, {{{ splitI64('offset') }}}, {{{ splitI64('length') }}}));
     },
-    // TODO: mmap
-    // TODO: msync
-    // TODO: munmap
+    mmap: (stream, length, offset, prot, flags) => {
+      var buf = FS.handleError(__wasmfs_mmap(length, prot, flags, stream.fd, {{{ splitI64('offset') }}}));
+      return { ptr: buf, allocated: true };
+    },
+    // offset is passed to msync to maintain backwards compatability with the legacy JS API but is not used by WasmFS.
+    msync: (stream, bufferPtr, offset, length, mmapFlags) => {
+      assert(offset === 0);
+      // TODO: assert that stream has the fd corresponding to the mapped buffer (bufferPtr).
+      return FS.handleError(__wasmfs_msync(bufferPtr, length, mmapFlags));
+    },
+    munmap: (addr, length) => (
+      FS.handleError(__wasmfs_munmap(addr, length))
+    ),
     writeFile: (path, data) => withStackSave(() => {
       var pathBuffer = stringToUTF8OnStack(path);
       if (typeof data == 'string') {

system/lib/wasmfs/js_api.cpp

@@ -253,6 +253,18 @@ int _wasmfs_ftruncate(int fd, off_t length) {
 
 int _wasmfs_close(int fd) { return __wasi_fd_close(fd); }
 
+int _wasmfs_mmap(size_t length, int prot, int flags, int fd, off_t offset) {
+  return __syscall_mmap2(0, length, prot, flags, fd, offset);
+}
+
+int _wasmfs_msync(void* addr, size_t length, int flags) {
+  return __syscall_msync((intptr_t)addr, length, flags);
+}
+
+int _wasmfs_munmap(void* addr, size_t length) {
+  return __syscall_munmap((intptr_t)addr, length);
+}
+
 int _wasmfs_utime(char* path, long atime_ms, long mtime_ms) {
   struct timespec times[2];
   times[0].tv_sec = atime_ms / 1000;
@@ -261,7 +273,7 @@ int _wasmfs_utime(char* path, long atime_ms, long mtime_ms) {
   times[1].tv_nsec = (mtime_ms % 1000) * 1000000;
 
   return __syscall_utimensat(AT_FDCWD, (intptr_t)path, (intptr_t)times, 0);
-};
+}
 
 int _wasmfs_stat(char* path, struct stat* statBuf) {
   return __syscall_stat64((intptr_t)path, (intptr_t)statBuf);

test/fs/test_fs_js_api.c

@@ -7,6 +7,7 @@
 
 #include <emscripten/emscripten.h>
 #include <stdio.h>
+#include <string.h>
 #include <unistd.h>
 #include <sys/stat.h>
 #include <assert.h>
@@ -333,6 +334,63 @@ void test_fs_truncate() {
     remove("truncatetest");
 }
 
+void test_fs_mmap() {
+    EM_ASM(
+        FS.writeFile('mmaptest', 'a=1_b=2_');
+
+        var stream = FS.open('mmaptest', 'r+');
+        assert(stream);
+
+        var mapped = FS.mmap(stream, 12, 0, 1 | 2 /* PROT_READ | PROT_WRITE */, 1 /* MAP_SHARED */);
+        var ret = new Uint8Array(Module.HEAPU8.subarray(mapped.ptr, mapped.ptr + 12));
+        var fileContents = "";
+        for (var i = 0; i < 12; i++) {
+            fileContents += String.fromCharCode(ret[i]);
+        }
+        assert(fileContents === 'a=1_b=2_\0\0\0\0');
+
+        ret[8] = ':'.charCodeAt(0);
+        ret[9] = 'x'.charCodeAt(0);
+        ret[10] = 'y'.charCodeAt(0);
+        ret[11] = 'z'.charCodeAt(0);
+        Module.HEAPU8.set(ret, mapped.ptr);
+
+        // The WasmFS msync syscall requires a pointer to the mapped memory, while the legacy JS API takes in any Uint8Array 
+        // buffer to write to a file.
+#if WASMFS
+        FS.msync(stream, mapped.ptr, 0, 12, 1 /* MAP_SHARED */);
+
+        var ex;
+        try {
+            FS.munmap(mapped.ptr, 4);
+        } catch (err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+
+        FS.munmap(mapped.ptr, 12);
+
+        // WasmFS correctly handles unmapping, while the legacy JS API does not.
+        try {
+            FS.msync(stream, mapped.ptr, 0, 12, 1 /* MAP_SHARED */);
+        } catch (err) {
+            ex = err;
+        }
+        assert(ex.name === "ErrnoError" && ex.errno === 28 /* EINVAL */);
+#else
+        FS.msync(stream, new Uint8Array(ret), 0, 12, 1 /* MAP_SHARED */);
+        FS.munmap(stream);
+#endif
+    );
+
+    FILE *fptr = fopen("mmaptest", "r");
+    char res[13];
+    fgets(res, 13, fptr);
+    assert(strcmp(res, "a=1_b=2_:xyz") == 0);
+
+    remove("mmaptest");
+}
+
 void test_fs_mkdirTree() {
     EM_ASM(
         FS.mkdirTree("/test1/test2/test3");
@@ -413,6 +471,10 @@ int main() {
     test_fs_mknod();
     test_fs_allocate();
     test_fs_truncate();
+#if WASMFS
+    // TODO: Fix legacy API FS.mmap bug involving emscripten_builtin_memalign
+    test_fs_mmap();
+#endif
     test_fs_mkdirTree();
     test_fs_utime();