1 /* $OpenBSD: seekdir.c,v 1.13 2015/09/12 13:34:22 guenther Exp $ */
2 /*
3 * Copyright (c) 2013 Ingo Schwarze <schwarze@openbsd.org>
4 *
5 * Permission to use, copy, modify, and distribute this software for any
6 * purpose with or without fee is hereby granted, provided that the above
7 * copyright notice and this permission notice appear in all copies.
8 *
9 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
10 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
11 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
12 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
13 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
14 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
15 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
16 */
17
18 #include <dirent.h>
19 #include <unistd.h>
20
21 #include "thread_private.h"
22 #include "telldir.h"
23
24 /*
25 * Seek to an entry in a directory.
26 * Only values returned by "telldir" should be passed to seekdir.
27 */
28 void
seekdir(DIR * dirp,long loc)29 seekdir(DIR *dirp, long loc)
30 {
31 struct dirent *dp;
32
33 /*
34 * First check whether the directory entry to seek for
35 * is still buffered in the directory structure in memory.
36 */
37
38 _MUTEX_LOCK(&dirp->dd_lock);
39 if (dirp->dd_size && dirp->dd_bufpos == loc) {
40 dirp->dd_loc = 0;
41 dirp->dd_curpos = loc;
42 _MUTEX_UNLOCK(&dirp->dd_lock);
43 return;
44 }
45
46 for (dirp->dd_loc = 0;
47 dirp->dd_loc < dirp->dd_size;
48 dirp->dd_loc += dp->d_reclen) {
49 dp = (struct dirent *)(dirp->dd_buf + dirp->dd_loc);
50 if (dp->d_off != loc)
51 continue;
52
53 /*
54 * Entry found in the buffer, use it. If readdir(3)
55 * follows, this will save us a getdents(2) syscall.
56 * Note that d_off is the offset of the _next_ entry,
57 * so advance dd_loc.
58 */
59
60 dirp->dd_loc += dp->d_reclen;
61 dirp->dd_curpos = loc;
62 _MUTEX_UNLOCK(&dirp->dd_lock);
63 return;
64 }
65
66 /*
67 * The entry is not in the buffer, prepare a call to getdents(2).
68 * In particular, invalidate dd_loc.
69 */
70
71 dirp->dd_loc = dirp->dd_size;
72 dirp->dd_bufpos = dirp->dd_curpos = lseek(dirp->dd_fd, loc, SEEK_SET);
73 _MUTEX_UNLOCK(&dirp->dd_lock);
74 }
75 DEF_WEAK(seekdir);
76