Make readdir on /proc/self/fd work (emscripten-core#23073)

Author: hoodmane

src/library_fs.js

@@ -1393,6 +1393,9 @@ FS.staticInit();
       FS.mount({
         mount() {
           var node = FS.createNode(proc_self, 'fd', {{{ cDefs.S_IFDIR | 0o777 }}}, {{{ cDefs.S_IXUGO }}});
+          node.stream_ops = {
+            llseek: MEMFS.stream_ops.llseek,
+          };
           node.node_ops = {
             lookup(parent, name) {
               var fd = +name;
@@ -1401,9 +1404,15 @@ FS.staticInit();
                 parent: null,
                 mount: { mountpoint: 'fake' },
                 node_ops: { readlink: () => stream.path },
+                id: fd + 1,
               };
               ret.parent = ret; // make it look like a simple root node
               return ret;
+            },
+            readdir() {
+              return Array.from(FS.streams.entries())
+                .filter(([k, v]) => v)
+                .map(([k, v]) => k.toString());
             }
           };
           return node;

test/fs/test_proc_self_fd.c

@@ -14,8 +14,6 @@ int main(int argc, char* argv[]) {
   struct dirent *entry;
   while ((entry = readdir(d))) {
     printf("entry: %s\n", entry->d_name);
-    printf("unexpected success reading directory!");
-    return 1;
   }
   closedir(d);
 

test/fs/test_proc_self_fd.out

@@ -1,2 +1,6 @@
+entry: 0
+entry: 1
+entry: 2
+entry: 3
 fd0: /dev/tty
 done