Remove readlink functions from worker and lz4 fs (#18646)

Author: arsnyder16

src/library_lz4.js

@@ -134,9 +134,6 @@ mergeInto(LibraryManager.library, {
       symlink: function(parent, newName, oldPath) {
         throw new FS.ErrnoError({{{ cDefine('EPERM') }}});
       },
-      readlink: function(node) {
-        throw new FS.ErrnoError({{{ cDefine('EPERM') }}});
-      },
     },
     stream_ops: {
       read: function (stream, buffer, offset, length, position) {

src/library_workerfs.js

@@ -127,9 +127,6 @@ mergeInto(LibraryManager.library, {
       symlink: function(parent, newName, oldPath) {
         throw new FS.ErrnoError({{{ cDefine('EPERM') }}});
       },
-      readlink: function(node) {
-        throw new FS.ErrnoError({{{ cDefine('EPERM') }}});
-      },
     },
     stream_ops: {
       read: function (stream, buffer, offset, length, position) {

test/fs/test_lz4fs.cpp

@@ -7,6 +7,8 @@
 #include <string.h>
 #include <stdlib.h>
 #include <assert.h>
+#include <unistd.h>
+#include <errno.h>
 
 #include <emscripten.h>
 
@@ -114,6 +116,15 @@ extern "C" void EMSCRIPTEN_KEEPALIVE finish() {
   fclose(f2);
   fclose(f3);
 
+  // attemping to read a lz4 node as a link should be invalid
+  buffer[0] = '\0';
+  assert(readlink("file1.txt", buffer, sizeof(buffer)) == -1);
+  assert(buffer[0] == '\0');
+  assert(errno == EINVAL);
+  assert(readlink("subdir/file2.txt", buffer, sizeof(buffer)) == -1);
+  assert(buffer[0] == '\0');
+  assert(errno == EINVAL);
+
   // all done
   int result;
 #if LOAD_MANUALLY

test/fs/test_workerfs_read.c

@@ -72,5 +72,12 @@ int main() {
 
   assert(blobFileExists);
   assert(fileTxtExists);
+
+  // attemping to read a worker node as a link should result in EINVAL
+  buf[0] = '\0';
+  assert(readlink("/work/blob.txt", buf, sizeof(buf)) == -1);
+  assert(buf[0] == '\0');
+  assert(errno == EINVAL);
+
   return 0;
 }