Fix some edge cases with rewinddir():

- In the unionfs case, opendir() and fdopendir() read the directory's full
  contents and cache it.  This cache is not refreshed when rewinddir() is
  called, so rewinddir() will not notice updates to a directory.  Fix this
  by splitting the code to fetch a directory's contents out of
  __opendir_common() into a new _filldir() function and call this from
  rewinddir() when operating on a unionfs directory.
- If rewinddir() is called on a directory opened with fdopendir() before
  any directory entries are fetched, rewinddir() will not adjust the seek
  location of the backing file descriptor.  If the file descriptor passed
  to fdopendir() had a non-zero offset, the rewinddir() will not rewind to
  the beginning.  Fix this by always seeking back to 0 in rewinddir().
  This means the dd_rewind hack can also be removed.

While here, add missing locking to rewinddir().

CR:   	    	https://phabric.freebsd.org/D312
Reviewed by:	jilles
MFC after:	1 week

1 files changed, 1 insertions, 0 deletions

diff --git a/include/dirent.h b/include/dirent.h
index c77d844e399b..b894bb845329 100644
--- a/include/dirent.h
+++ b/include/dirent.h
@@ -63,6 +63,7 @@ typedef struct _dirdesc DIR;
 #define DTF_NODUP	0x0002	/* don't return duplicate names */
 #define DTF_REWIND	0x0004	/* rewind after reading union stack */
 #define __DTF_READALL	0x0008	/* everything has been read */
+#define	__DTF_SKIPREAD	0x0010  /* assume internal buffer is populated */
 
 #else /* !__BSD_VISIBLE */