If fd_readdir returns a zero inode, call fstatat to get the inode…

… value.

On some systems, `fd_readdir` may not implement the `d_ino` field and
may set it to zero. When this happens, have wasi-libc call `fstatat` to
get the inode number.

See the discussion in
WebAssembly/wasi-filesystem#65 for details.

libc-bottom-half/cloudlibc/src/libc/dirent/readdir.c

@@ -38,6 +38,8 @@ static_assert(DT_UNKNOWN == __WASI_FILETYPE_UNKNOWN, "Value mismatch");
   } while (0)
 
 struct dirent *readdir(DIR *dirp) {
+  struct stat statbuf;
+
   for (;;) {
     // Extract the next dirent header.
     size_t buffer_left = dirp->buffer_used - dirp->buffer_processed;
@@ -72,12 +74,24 @@ struct dirent *readdir(DIR *dirp) {
       continue;
     }
 
+    // `fd_readdir` implementations may set the inode field to zero if the
+    // the inode number is unknown. In that case, do an `fstatat` to get the
+    // inode number.
+    off_t d_ino = entry.d_ino;
+    if (d_ino == 0) {
+      if (fstatat(dirp->fd, entry.d_name, &statbuf, AT_SYMLINK_NOFOLLOW) != 0) {
+        return NULL;
+      }
+
+      d_ino = statbuf.st_ino;
+    }
+
     // Return the next directory entry. Ensure that the dirent is large
     // enough to fit the filename.
     GROW(dirp->dirent, dirp->dirent_size,
          offsetof(struct dirent, d_name) + entry.d_namlen + 1);
     struct dirent *dirent = dirp->dirent;
-    dirent->d_ino = entry.d_ino;
+    dirent->d_ino = d_ino;
     dirent->d_type = entry.d_type;
     memcpy(dirent->d_name, name, entry.d_namlen);
     dirent->d_name[entry.d_namlen] = '\0';

libc-bottom-half/cloudlibc/src/libc/dirent/scandirat.c

@@ -84,12 +84,24 @@ int __wasilibc_nocwd_scandirat(int dirfd, const char *dir, struct dirent ***name
     if (memchr(name, '\0', entry.d_namlen) != NULL)
       continue;
 
+    // `fd_readdir` implementations may set the inode field to zero if the
+    // the inode number is unknown. In that case, do an `fstatat` to get the
+    // inode number.
+    off_t d_ino = entry.d_ino;
+    if (d_ino == 0) {
+      if (fstatat(dirp->fd, entry.d_name, &statbuf, AT_SYMLINK_NOFOLLOW) != 0) {
+        return NULL;
+      }
+
+      d_ino = statbuf.st_ino;
+    }
+
     // Create the new directory entry.
     struct dirent *dirent =
         malloc(offsetof(struct dirent, d_name) + entry.d_namlen + 1);
     if (dirent == NULL)
       goto bad;
-    dirent->d_ino = entry.d_ino;
+    dirent->d_ino = d_ino;
     dirent->d_type = entry.d_type;
     memcpy(dirent->d_name, name, entry.d_namlen);
     dirent->d_name[entry.d_namlen] = '\0';