76 lines
2.1 KiB
C
76 lines
2.1 KiB
C
/* $OpenBSD: seekdir.c,v 1.13 2015/09/12 13:34:22 guenther Exp $ */
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/*
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* Copyright (c) 2013 Ingo Schwarze <schwarze@openbsd.org>
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*
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* Permission to use, copy, modify, and distribute this software for any
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* purpose with or without fee is hereby granted, provided that the above
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* copyright notice and this permission notice appear in all copies.
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*
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* THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
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* WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
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* MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
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* ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
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* WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
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* ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
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* OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
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*/
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#include <dirent.h>
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#include <unistd.h>
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#include "thread_private.h"
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#include "telldir.h"
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/*
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* Seek to an entry in a directory.
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* Only values returned by "telldir" should be passed to seekdir.
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*/
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void
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seekdir(DIR *dirp, long loc)
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{
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struct dirent *dp;
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/*
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* First check whether the directory entry to seek for
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* is still buffered in the directory structure in memory.
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*/
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_MUTEX_LOCK(&dirp->dd_lock);
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if (dirp->dd_size && dirp->dd_bufpos == loc) {
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dirp->dd_loc = 0;
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dirp->dd_curpos = loc;
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_MUTEX_UNLOCK(&dirp->dd_lock);
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return;
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}
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for (dirp->dd_loc = 0;
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dirp->dd_loc < dirp->dd_size;
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dirp->dd_loc += dp->d_reclen) {
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dp = (struct dirent *)(dirp->dd_buf + dirp->dd_loc);
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if (dp->d_off != loc)
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continue;
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/*
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* Entry found in the buffer, use it. If readdir(3)
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* follows, this will save us a getdents(2) syscall.
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* Note that d_off is the offset of the _next_ entry,
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* so advance dd_loc.
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*/
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dirp->dd_loc += dp->d_reclen;
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dirp->dd_curpos = loc;
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_MUTEX_UNLOCK(&dirp->dd_lock);
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return;
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}
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/*
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* The entry is not in the buffer, prepare a call to getdents(2).
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* In particular, invalidate dd_loc.
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*/
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dirp->dd_loc = dirp->dd_size;
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dirp->dd_bufpos = dirp->dd_curpos = lseek(dirp->dd_fd, loc, SEEK_SET);
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_MUTEX_UNLOCK(&dirp->dd_lock);
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}
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DEF_WEAK(seekdir);
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