Implement _read_directory_iterator in os2.

Also, fix minor bug in linux.dirent_name.

core/os/os2/dir_linux.odin

@@ -1,20 +1,101 @@
 #+private
 package os2
 
+import "core:sys/linux"
+
 Read_Directory_Iterator_Impl :: struct {
-
+	prev_fi:        File_Info,
+	dirent_backing: []u8,
+	dirent_buflen:  int,
+	dirent_off:     int,
+	index:          int,
 }
 
-
 @(require_results)
 _read_directory_iterator :: proc(it: ^Read_Directory_Iterator) -> (fi: File_Info, index: int, ok: bool) {
+	scan_entries :: proc(dfd: linux.Fd, entries: []u8, offset: ^int) -> (fd: linux.Fd, file_name: string) {
+		for d in linux.dirent_iterate_buf(entries, offset) {
+			file_name = linux.dirent_name(d)
+			if file_name == "." || file_name == ".." {
+				continue
+			}
+
+			file_name_cstr := cstring(raw_data(file_name))
+			entry_fd, errno := linux.openat(dfd, file_name_cstr, {.NOFOLLOW, .PATH})
+			if errno == .NONE {
+				return entry_fd, file_name
+			}
+		}
+		return -1, ""
+	}
+
+	index = it.impl.index
+	it.impl.index += 1
+
+	dfd := linux.Fd(_fd(it.f))
+
+	entries := it.impl.dirent_backing[:it.impl.dirent_buflen]
+	entry_fd, file_name := scan_entries(dfd, entries, &it.impl.dirent_off)
+
+	for entry_fd == -1 {
+		if len(it.impl.dirent_backing) == 0 {
+			it.impl.dirent_backing = make([]u8, 512, file_allocator())
+		}
+
+		loop: for {
+			buflen, errno := linux.getdents(linux.Fd(dfd), it.impl.dirent_backing[:])
+			#partial switch errno {
+			case .EINVAL:
+				delete(it.impl.dirent_backing, file_allocator())
+				n := len(it.impl.dirent_backing) * 2
+				it.impl.dirent_backing = make([]u8, n, file_allocator())
+				continue
+			case .NONE:
+				if buflen == 0 {
+					return
+				}
+				it.impl.dirent_off = 0
+				it.impl.dirent_buflen = buflen
+				entries = it.impl.dirent_backing[:buflen]
+				break loop
+			case: // error
+				return
+			}
+		}
+
+		entry_fd, file_name = scan_entries(dfd, entries, &it.impl.dirent_off)
+	}
+	defer linux.close(entry_fd)
+
+	file_info_delete(it.impl.prev_fi, file_allocator())
+	fi, _ = _fstat_internal(entry_fd, file_allocator())
+	it.impl.prev_fi = fi
+
+	ok = true
 	return
 }
 
 @(require_results)
 _read_directory_iterator_create :: proc(f: ^File) -> (Read_Directory_Iterator, Error) {
-	return {}, .Unsupported
+	if f == nil || f.impl == nil {
+		return {}, .Invalid_File
+	}
+
+	stat: linux.Stat
+	errno := linux.fstat(linux.Fd(fd(f)), &stat)
+	if errno != .NONE {
+		return {}, _get_platform_error(errno)
+	}
+	if (stat.mode & linux.S_IFMT) != linux.S_IFDIR {
+		return {}, .Invalid_Dir
+	}
+	return {f = f}, nil
 }
 
 _read_directory_iterator_destroy :: proc(it: ^Read_Directory_Iterator) {
+	if it == nil {
+		return
+	}
+	delete(it.impl.dirent_backing, file_allocator())
+	file_info_delete(it.impl.prev_fi, file_allocator())
 }