[FS] Make fstat work on file descriptors with no name in node rawfs (#23364)

This fixes fstat on "anonymous" file descriptors in node rawfs. It is
split off from #23058.

Author: hoodmane

src/lib/libfs.js

@@ -965,6 +965,9 @@ FS.staticInit();
       var getattr = FS.checkOpExists(node.node_ops.getattr, {{{ cDefs.EPERM }}});
       return getattr(node);
     },
+    fstat(fd) {
+      return FS.stat(FS.getStreamChecked(fd).path);
+    },
     lstat(path) {
       return FS.stat(path, true);
     },

src/lib/libnoderawfs.js

@@ -80,6 +80,10 @@ addToLibrary({
       }
       return stat;
     },
+    fstat(fd) {
+      var stream = FS.getStreamChecked(fd);
+      return fs.fstatSync(stream.nfd);
+    },
     statfsStream(stream) {
       return fs.statfsSync(stream.path);
     },

src/lib/libsyscall.js

@@ -690,8 +690,7 @@ var SyscallsLibrary = {
     return SYSCALLS.writeStat(buf, FS.lstat(path));
   },
   __syscall_fstat64: (fd, buf) => {
-    var stream = SYSCALLS.getStreamFromFD(fd);
-    return SYSCALLS.writeStat(buf, FS.stat(stream.path));
+    return SYSCALLS.writeStat(buf, FS.fstat(fd));
   },
   __syscall_fchown32: (fd, owner, group) => {
     FS.fchown(fd, owner, group);

test/fs/test_stat_unnamed_file_descriptor.c

@@ -0,0 +1,20 @@
+#include <fcntl.h>
+#include <unistd.h>
+#include <sys/stat.h>
+#include <assert.h>
+#include "stdio.h"
+
+int main() {
+  int fd = open("file.txt", O_RDWR | O_CREAT, 0666);
+  unlink("file.txt");
+  int res;
+  struct stat buf;
+  res = fstat(fd, &buf);
+  assert(res == 0);
+  assert(buf.st_atime > 1000000000);
+  res = fchmod(fd, 0777);
+  assert(res == 0);
+  res = ftruncate(fd, 10);
+  assert(res == 0);
+  printf("success\n");
+}

test/other/codesize/test_codesize_cxx_ctors1.size

@@ -1 +1 @@
-129211
+129218

test/other/codesize/test_codesize_cxx_ctors2.size

@@ -1 +1 @@
-128623
+128630

test/other/codesize/test_codesize_cxx_except.size

@@ -1 +1 @@
-170879
+170886

test/other/codesize/test_codesize_cxx_except_wasm.size

@@ -1 +1 @@
-144708
+144715

test/other/codesize/test_codesize_cxx_except_wasm_legacy.size

@@ -1 +1 @@
-142162
+142169

test/other/codesize/test_codesize_cxx_mangle.size

@@ -1 +1 @@
-232724
+232731