From b02c147c052fb3c7672e8ba8c15975c31d56a066 Mon Sep 17 00:00:00 2001
From: Ingo Weinhold <ingo_weinhold@gmx.de>
Date: Tue, 25 Aug 2009 22:16:40 +0000
Subject: [PATCH] Implemented seekdir() and telldir(). They were declared in
 <dirent.h> already. So either +alphabranch or remove the declarations from
 <dirent.h>.

git-svn-id: file:///srv/svn/repos/haiku/haiku/trunk@32679 a95241bf-73f2-0310-859d-f6bbb57e9c96
---
 headers/private/libroot/dirent_private.h |   2 +
 src/system/libroot/posix/dirent.c        | 105 ++++++++++++++++++++---
 2 files changed, 96 insertions(+), 11 deletions(-)

diff --git a/headers/private/libroot/dirent_private.h b/headers/private/libroot/dirent_private.h
index 785549bac4..5e39f7b994 100644
--- a/headers/private/libroot/dirent_private.h
+++ b/headers/private/libroot/dirent_private.h
@@ -16,6 +16,8 @@ struct __DIR {
 	int				fd;
 	short			next_entry;
 	unsigned short	entries_left;
+	long			seek_position;
+	long			current_position;
 	struct dirent	first_entry;
 };
 
diff --git a/src/system/libroot/posix/dirent.c b/src/system/libroot/posix/dirent.c
index 5274d9e246..cee73ff75a 100644
--- a/src/system/libroot/posix/dirent.c
+++ b/src/system/libroot/posix/dirent.c
@@ -1,4 +1,5 @@
 /*
+ * Copyright 2009, Ingo Weinhold, ingo_weinhold@gmx.de.
  * Copyright 2004-2008, Axel Dörfler, axeld@pinc-software.de.
  * Distributed under the terms of the MIT License.
  */
@@ -11,14 +12,75 @@
 
 #include <dirent_private.h>
 #include <syscalls.h>
+#include <syscall_utils.h>
 
 
-#define RETURN_AND_SET_ERRNO(err) \
-	if (err < 0) { \
-		errno = err; \
-		return -1; \
-	} \
-	return err;
+static int
+do_seek_dir(DIR* dir)
+{
+	if (dir->seek_position == dir->current_position)
+		return 0;
+
+	// If the seek position lies before the current position (the usual case),
+	// rewind to the beginning.
+	if (dir->seek_position < dir->current_position) {
+		status_t status = _kern_rewind_dir(dir->fd);
+		if (status < 0) {
+			errno = status;
+			return -1;
+		}
+
+		dir->current_position = 0;
+		dir->entries_left = 0;
+	}
+
+	// Now skip entries until we have reached seek_position.
+	while (dir->seek_position > dir->current_position) {
+		ssize_t count;
+		long toSkip = dir->seek_position - dir->current_position;
+		if (toSkip == dir->entries_left) {
+			// we have to skip exactly all of the currently buffered entries
+			dir->current_position = dir->seek_position;
+			dir->entries_left = 0;
+			return 0;
+		}
+
+		if (toSkip < dir->entries_left) {
+			// we have to skip only some of the buffered entries
+			for (; toSkip > 0; toSkip--) {
+				struct dirent* entry = (struct dirent*)
+					((uint8*)&dir->first_entry + dir->next_entry);
+				dir->entries_left--;
+				dir->next_entry += entry->d_reclen;
+			}
+
+			dir->current_position = dir->seek_position;
+			return 0;
+		}
+
+		// we have to skip more than the currently buffered entries
+		dir->current_position += dir->entries_left;
+		dir->entries_left = 0;
+
+		count = _kern_read_dir(dir->fd, &dir->first_entry, DIRENT_BUFFER_SIZE,
+			USHRT_MAX);
+		if (count <= 0) {
+			if (count < 0)
+				errno = count;
+
+			// end of directory
+			return -1;
+		}
+
+		dir->next_entry = 0;
+		dir->entries_left = count;
+	}
+
+	return 0;
+}
+
+
+// #pragma mark -
 
 
 DIR *
@@ -41,6 +103,8 @@ opendir(const char *path)
 
 	dir->fd = fd;
 	dir->entries_left = 0;
+	dir->seek_position = 0;
+	dir->current_position = 0;
 
 	return dir;
 }
@@ -62,12 +126,19 @@ readdir(DIR *dir)
 {
 	ssize_t count;
 
+	if (dir->seek_position != dir->current_position) {
+		if (do_seek_dir(dir) != 0)
+			return NULL;
+	}
+
 	if (dir->entries_left > 0) {
 		struct dirent *dirent
 			= (struct dirent *)((uint8 *)&dir->first_entry + dir->next_entry);
 
 		dir->entries_left--;
 		dir->next_entry += dirent->d_reclen;
+		dir->seek_position++;
+		dir->current_position++;
 
 		return dirent;
 	}
@@ -86,6 +157,8 @@ readdir(DIR *dir)
 
 	dir->entries_left = count - 1;
 	dir->next_entry = dir->first_entry.d_reclen;
+	dir->seek_position++;
+	dir->current_position++;
 
 	return &dir->first_entry;
 }
@@ -112,11 +185,21 @@ readdir_r(DIR *dir, struct dirent *entry, struct dirent **_result)
 void
 rewinddir(DIR *dir)
 {
-	status_t status = _kern_rewind_dir(dir->fd);
-	if (status < 0)
-		errno = status;
-	else
-		dir->entries_left = 0;
+	dir->seek_position = 0;
+}
+
+
+void
+seekdir(DIR* dir, long int position)
+{
+	dir->seek_position = position;
+}
+
+
+long int
+telldir(DIR* dir)
+{
+	return dir->seek_position;
 }