5 files changed, 69 insertions, 1 deletions

diff --git a/lib/libc/gen/directory.3 b/lib/libc/gen/directory.3
index 1e864f8..e1874da 100644
--- a/lib/libc/gen/directory.3
+++ b/lib/libc/gen/directory.3
@@ -267,4 +267,27 @@ The invalidation of
 .Fn telldir
 tokens when calling
 .Fn seekdir
-is non-standard.
+is non-standard. This is a compile time option.
+.Pp
+The behaviour of
+.Fn telldir
+and
+.Fn seekdir
+is likely to be wrong if there are parallel unlinks happening
+and the directory is larger than one page.
+There is code to ensure that a
+.Fn seekdir
+to the location given by a 
+.Fn telldir
+immediately before the last 
+.Fn readdir
+will always set the correct location to return the same value as that last
+.Fn readdir
+performed.
+This is enough for some applications which want to "push back the last entry read" E.g. Samba. 
+Seeks back to any other location,
+other than the beginning of the directory,
+may result in unexpected behaviour if deletes are present.
+It is hoped that this situation will be resolved with changes to
+.Fn getdirentries
+and the VFS.
diff --git a/lib/libc/gen/readdir.c b/lib/libc/gen/readdir.c
index 69f59d1..c6f5d3f 100644
--- a/lib/libc/gen/readdir.c
+++ b/lib/libc/gen/readdir.c
@@ -54,19 +54,25 @@ _readdir_unlocked(dirp, skip)
 	int skip;
 {
 	struct dirent *dp;
+	long initial_seek;
+	long initial_loc = 0;
 
 	for (;;) {
 		if (dirp->dd_loc >= dirp->dd_size) {
 			if (dirp->dd_flags & __DTF_READALL)
 				return (NULL);
+			initial_loc = dirp->dd_loc;
+			dirp->dd_flags &= ~__DTF_SKIPREAD;
 			dirp->dd_loc = 0;
 		}
 		if (dirp->dd_loc == 0 &&
 		    !(dirp->dd_flags & (__DTF_READALL | __DTF_SKIPREAD))) {
+			initial_seek = dirp->dd_seek;
 			dirp->dd_size = _getdirentries(dirp->dd_fd,
 			    dirp->dd_buf, dirp->dd_len, &dirp->dd_seek);
 			if (dirp->dd_size <= 0)
 				return (NULL);
+			_fixtelldir(dirp, initial_seek, initial_loc);
 		}
 		dirp->dd_flags &= ~__DTF_SKIPREAD;
 		dp = (struct dirent *)(dirp->dd_buf + dirp->dd_loc);
diff --git a/lib/libc/gen/rewinddir.c b/lib/libc/gen/rewinddir.c
index 193f4b0..e157cd6 100644
--- a/lib/libc/gen/rewinddir.c
+++ b/lib/libc/gen/rewinddir.c
@@ -51,6 +51,7 @@ rewinddir(dirp)
 
 	if (__isthreaded)
 		_pthread_mutex_lock(&dirp->dd_lock);
+	dirp->dd_flags &= ~__DTF_SKIPREAD; /* current contents are invalid */
 	if (dirp->dd_flags & __DTF_READALL)
 		_filldir(dirp, false);
 	else {
diff --git a/lib/libc/gen/telldir.c b/lib/libc/gen/telldir.c
index d72b500..19cd6ee 100644
--- a/lib/libc/gen/telldir.c
+++ b/lib/libc/gen/telldir.c
@@ -101,9 +101,22 @@ _seekdir(dirp, loc)
 		return;
 	if (lp->loc_loc == dirp->dd_loc && lp->loc_seek == dirp->dd_seek)
 		return;
+
+	/* If it's within the same chunk of data, don't bother reloading. */
+	if (lp->loc_seek == dirp->dd_seek) {
+		/*
+		 * If we go back to 0 don't make the next readdir
+		 * trigger a call to getdirentries().
+		 */
+		if (lp->loc_loc == 0)
+			dirp->dd_flags |= __DTF_SKIPREAD;
+		dirp->dd_loc = lp->loc_loc;
+		return;
+	}
 	(void) lseek(dirp->dd_fd, (off_t)lp->loc_seek, SEEK_SET);
 	dirp->dd_seek = lp->loc_seek;
 	dirp->dd_loc = 0;
+	dirp->dd_flags &= ~__DTF_SKIPREAD; /* current contents are invalid */
 	while (dirp->dd_loc < lp->loc_loc) {
 		dp = _readdir_unlocked(dirp, 0);
 		if (dp == NULL)
@@ -112,6 +125,30 @@ _seekdir(dirp, loc)
 }
 
 /*
+ * After readdir returns the last entry in a block, a call to telldir
+ * returns a location that is after the end of that last entry.
+ * However, that location doesn't refer to a valid directory entry.
+ * Ideally, the call to telldir would return a location that refers to
+ * the first entry in the next block.  That location is not known
+ * until the next block is read, so readdir calls this function after
+ * fetching a new block to fix any such telldir locations.
+ */
+void
+_fixtelldir(DIR *dirp, long oldseek, long oldloc)
+{
+	struct ddloc *lp;
+
+	lp = LIST_FIRST(&dirp->dd_td->td_locq);
+	if (lp != NULL) {
+		if (lp->loc_loc == oldloc &&
+		    lp->loc_seek == oldseek) {
+			lp->loc_seek = dirp->dd_seek;
+			lp->loc_loc = dirp->dd_loc;
+		}
+	}
+}
+
+/*
  * Reclaim memory for telldir cookies which weren't used.
  */
 void
diff --git a/lib/libc/gen/telldir.h b/lib/libc/gen/telldir.h
index 04989bb..bccabb1 100644
--- a/lib/libc/gen/telldir.h
+++ b/lib/libc/gen/telldir.h
@@ -64,5 +64,6 @@ bool		_filldir(DIR *, bool);
 struct dirent	*_readdir_unlocked(DIR *, int);
 void 		_reclaim_telldir(DIR *);
 void 		_seekdir(DIR *, long);
+void		_fixtelldir(DIR *dirp, long oldseek, long oldloc);
 
 #endif