4 files changed, 69 insertions, 1 deletions

diff --git a/libc/bionic/dirent.cpp b/libc/bionic/dirent.cpp
index 5e1c7a5..6d87097 100644
--- a/libc/bionic/dirent.cpp
+++ b/libc/bionic/dirent.cpp
@@ -43,6 +43,7 @@ struct DIR {
   int fd_;
   size_t available_bytes_;
   dirent* next_;
+  long current_pos_;
   pthread_mutex_t mutex_;
   dirent buff_[15];
 };
@@ -55,6 +56,7 @@ static DIR* __allocate_DIR(int fd) {
   d->fd_ = fd;
   d->available_bytes_ = 0;
   d->next_ = NULL;
+  d->current_pos_ = 0L;
   pthread_mutex_init(&d->mutex_, NULL);
   return d;
 }
@@ -100,6 +102,9 @@ static dirent* __readdir_locked(DIR* d) {
   dirent* entry = d->next_;
   d->next_ = reinterpret_cast<dirent*>(reinterpret_cast<char*>(entry) + entry->d_reclen);
   d->available_bytes_ -= entry->d_reclen;
+  // The directory entry offset uses 0, 1, 2 instead of real file offset,
+  // so the value range of long type is enough.
+  d->current_pos_ = static_cast<long>(entry->d_off);
   return entry;
 }
 
@@ -146,6 +151,20 @@ void rewinddir(DIR* d) {
   ScopedPthreadMutexLocker locker(&d->mutex_);
   lseek(d->fd_, 0, SEEK_SET);
   d->available_bytes_ = 0;
+  d->current_pos_ = 0L;
+}
+
+void seekdir(DIR* d, long offset) {
+  ScopedPthreadMutexLocker locker(&d->mutex_);
+  off_t ret = lseek(d->fd_, offset, SEEK_SET);
+  if (ret != -1L) {
+    d->available_bytes_ = 0;
+    d->current_pos_ = ret;
+  }
+}
+
+long telldir(DIR* d) {
+  return d->current_pos_;
 }
 
 int alphasort(const dirent** a, const dirent** b) {
diff --git a/libc/include/dirent.h b/libc/include/dirent.h
index 4ca3a7d..63716a4 100644
--- a/libc/include/dirent.h
+++ b/libc/include/dirent.h
@@ -76,6 +76,8 @@ extern int readdir_r(DIR*, struct dirent*, struct dirent**);
 extern int readdir64_r(DIR*, struct dirent64*, struct dirent64**);
 extern int closedir(DIR*);
 extern void rewinddir(DIR*);
+extern void seekdir(DIR*, long);
+extern long telldir(DIR*);
 extern int dirfd(DIR*);
 extern int alphasort(const struct dirent**, const struct dirent**);
 extern int alphasort64(const struct dirent64**, const struct dirent64**);
diff --git a/tests/dirent_test.cpp b/tests/dirent_test.cpp
index 6aadb37..214dd78 100644
--- a/tests/dirent_test.cpp
+++ b/tests/dirent_test.cpp
@@ -231,3 +231,50 @@ TEST(dirent, rewinddir) {
     ASSERT_EQ(pass1[i], pass2[i]);
   }
 }
+
+TEST(dirent, seekdir_telldir) {
+  DIR* d = opendir("/proc/self");
+  ASSERT_TRUE(d != NULL);
+  std::vector<long> offset_list;
+  std::vector<std::string> name_list;
+  dirent* e = NULL;
+
+  offset_list.push_back(telldir(d));
+  ASSERT_EQ(0L, offset_list.back());
+
+  while ((e = readdir(d)) != NULL) {
+    name_list.push_back(e->d_name);
+    offset_list.push_back(telldir(d));
+    // Make sure telldir() point to the next entry.
+    ASSERT_EQ(e->d_off, offset_list.back());
+  }
+
+  long end_offset = telldir(d);
+  // telldir() should not pass the end of the file.
+  ASSERT_EQ(offset_list.back(), end_offset);
+  offset_list.pop_back();
+
+  for (size_t i = 0; i < offset_list.size(); ++i) {
+    seekdir(d, offset_list[i]);
+    ASSERT_EQ(offset_list[i], telldir(d));
+    e = readdir(d);
+    ASSERT_TRUE(e != NULL);
+    ASSERT_STREQ(name_list[i].c_str(), e->d_name);
+  }
+  for (int i = static_cast<int>(offset_list.size()) - 1; i >= 0; --i) {
+    seekdir(d, offset_list[i]);
+    ASSERT_EQ(offset_list[i], telldir(d));
+    e = readdir(d);
+    ASSERT_TRUE(e != NULL);
+    ASSERT_STREQ(name_list[i].c_str(), e->d_name);
+  }
+
+  // Seek to the end, read NULL.
+  seekdir(d, end_offset);
+  ASSERT_EQ(end_offset, telldir(d));
+  errno = 0;
+  ASSERT_EQ(NULL, readdir(d));
+  ASSERT_EQ(0, errno);
+
+  ASSERT_EQ(0, closedir(d));
+}
diff --git a/tests/stdio_test.cpp b/tests/stdio_test.cpp
index 549792e..6be372c 100644
--- a/tests/stdio_test.cpp
+++ b/tests/stdio_test.cpp
@@ -77,7 +77,7 @@ TEST(stdio, dprintf) {
   int rc = dprintf(tf.fd, "hello\n");
   ASSERT_EQ(rc, 6);
 
-  lseek(tf.fd, SEEK_SET, 0);
+  lseek(tf.fd, 0, SEEK_SET);
   FILE* tfile = fdopen(tf.fd, "r");
   ASSERT_TRUE(tfile != NULL);