WasmFS JS API: Implement llseek (#19601)

Author: jameshu15869

.circleci/config.yml

@@ -532,6 +532,7 @@ jobs:
             wasmfs.test_unistd_links_memfs
             wasmfs.test_fcntl_open
             wasmfs.test_fs_js_api
+            wasmfs.test_fs_llseek
             wasmfs.test_freetype"
   test-wasm2js1:
     executor: bionic

emcc.py

@@ -2343,6 +2343,7 @@ def phase_linker_setup(options, state, newargs):
         '_wasmfs_chmod',
         '_wasmfs_fchmod',
         '_wasmfs_lchmod',
+        '_wasmfs_llseek',
         '_wasmfs_identify',
         '_wasmfs_readdir_start',
         '_wasmfs_readdir_get',

src/library_wasmfs.js

@@ -327,7 +327,9 @@ FS.createPreloadedFile = FS_createPreloadedFile;
       }));
     },
     // TODO: syncfs
-    // TODO: llseek
+    llseek: (stream, offset, whence) => {
+      return FS.handleError(__wasmfs_llseek(stream.fd, {{{ splitI64('offset') }}}, whence));
+    }
     // TODO: ioctl
 
 #endif

system/lib/wasmfs/js_api.cpp

@@ -181,6 +181,15 @@ int _wasmfs_lchmod(char* path, mode_t mode) {
   return __syscall_fchmodat(AT_FDCWD, (intptr_t)path, mode, AT_SYMLINK_NOFOLLOW);
 }
 
+int _wasmfs_llseek(int fd, off_t offset, int whence) {
+  __wasi_filesize_t newOffset;
+  int err = __wasi_fd_seek(fd, offset, whence, &newOffset);
+  if (err > 0) {
+    return -err;
+  }
+  return newOffset;
+}
+
 int _wasmfs_rename(char* oldpath, char* newpath) {
   return __syscall_renameat(AT_FDCWD, (intptr_t)oldpath, AT_FDCWD, (intptr_t)newpath);
 };