lib/replace/repdir_getdirentries.c

   1 /*
   2    Unix SMB/CIFS implementation.
   3
   4    Copyright (C) Andrew Tridgell 2005
   5
   6      ** NOTE! The following LGPL license applies to the replace
   7      ** library. This does NOT imply that all of Samba is released
   8      ** under the LGPL
   9
  10    This library is free software; you can redistribute it and/or
  11    modify it under the terms of the GNU Lesser General Public
  12    License as published by the Free Software Foundation; either
  13    version 3 of the License, or (at your option) any later version.
  14
  15    This library is distributed in the hope that it will be useful,
  16    but WITHOUT ANY WARRANTY; without even the implied warranty of
  17    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  18    Lesser General Public License for more details.
  19
  20    You should have received a copy of the GNU Lesser General Public
  21    License along with this library; if not, see <http://www.gnu.org/licenses/>.
  22 */
  23 /*
  24   a replacement for opendir/readdir/telldir/seekdir/closedir for BSD
  25   systems using getdirentries
  26
  27   This is needed because the existing directory handling in FreeBSD
  28   and OpenBSD (and possibly NetBSD) doesn't correctly handle unlink()
  29   on files in a directory where telldir() has been used. On a block
  30   boundary it will occasionally miss a file when seekdir() is used to
  31   return to a position previously recorded with telldir().
  32
  33   This also fixes a severe performance and memory usage problem with
  34   telldir() on BSD systems. Each call to telldir() in BSD adds an
  35   entry to a linked list, and those entries are cleaned up on
  36   closedir(). This means with a large directory closedir() can take an
  37   arbitrary amount of time, causing network timeouts as millions of
  38   telldir() entries are freed
  39
  40   Note! This replacement code is not portable. It relies on
  41   getdirentries() always leaving the file descriptor at a seek offset
  42   that is a multiple of DIR_BUF_SIZE. If the code detects that this
  43   doesn't happen then it will abort(). It also does not handle
  44   directories with offsets larger than can be stored in a long,
  45
  46   This code is available under other free software licenses as
  47   well. Contact the author.
  48 */
  49
  50 #include "replace.h"
  51 #include <stdlib.h>
  52 #include <sys/stat.h>
  53 #include <unistd.h>
  54 #include <sys/types.h>
  55 #include <errno.h>
  56 #include <fcntl.h>
  57 #include <dirent.h>
  58
  59 #define DIR_BUF_BITS 9
  60 #define DIR_BUF_SIZE (1<<DIR_BUF_BITS)
  61
  62 struct dir_buf {
  63         int fd;
  64         int nbytes, ofs;
  65         off_t seekpos;
  66         char buf[DIR_BUF_SIZE];
  67 };
  68
  69 DIR *opendir(const char *dname)
  70 {
  71         struct dir_buf *d;
  72         struct stat sb;
  73         d = malloc(sizeof(*d));
  74         if (d == NULL) {
  75                 errno = ENOMEM;
  76                 return NULL;
  77         }
  78         d->fd = open(dname, O_RDONLY);
  79         if (d->fd == -1) {
  80                 free(d);
  81                 return NULL;
  82         }
  83         if (fstat(d->fd, &sb) < 0) {
  84                 close(d->fd);
  85                 free(d);
  86                 return NULL;
  87         }
  88         if (!S_ISDIR(sb.st_mode)) {
  89                 close(d->fd);
  90                 free(d);
  91                 errno = ENOTDIR;
  92                 return NULL;
  93         }
  94         d->ofs = 0;
  95         d->seekpos = 0;
  96         d->nbytes = 0;
  97         return (DIR *)d;
  98 }
  99
 100 struct dirent *readdir(DIR *dir)
 101 {
 102         struct dir_buf *d = (struct dir_buf *)dir;
 103         struct dirent *de;
 104
 105         if (d->ofs >= d->nbytes) {
 106                 long pos;
 107                 d->nbytes = getdirentries(d->fd, d->buf, DIR_BUF_SIZE, &pos);
 108                 d->seekpos = pos;
 109                 d->ofs = 0;
 110         }
 111         if (d->ofs >= d->nbytes) {
 112                 return NULL;
 113         }
 114         de = (struct dirent *)&d->buf[d->ofs];
 115         d->ofs += de->d_reclen;
 116         return de;
 117 }
 118
 119 #ifdef TELLDIR_TAKES_CONST_DIR
 120 long telldir(const DIR *dir)
 121 #else
 122 long telldir(DIR *dir)
 123 #endif
 124 {
 125         struct dir_buf *d = (struct dir_buf *)dir;
 126         if (d->ofs >= d->nbytes) {
 127                 d->seekpos = lseek(d->fd, 0, SEEK_CUR);
 128                 d->ofs = 0;
 129                 d->nbytes = 0;
 130         }
 131         /* this relies on seekpos always being a multiple of
 132            DIR_BUF_SIZE. Is that always true on BSD systems? */
 133         if (d->seekpos & (DIR_BUF_SIZE-1)) {
 134                 abort();
 135         }
 136         return d->seekpos + d->ofs;
 137 }
 138
 139 #ifdef SEEKDIR_RETURNS_INT
 140 int seekdir(DIR *dir, long ofs)
 141 #else
 142 void seekdir(DIR *dir, long ofs)
 143 #endif
 144 {
 145         struct dir_buf *d = (struct dir_buf *)dir;
 146         long pos;
 147         d->seekpos = lseek(d->fd, ofs & ~(DIR_BUF_SIZE-1), SEEK_SET);
 148         d->nbytes = getdirentries(d->fd, d->buf, DIR_BUF_SIZE, &pos);
 149         d->ofs = 0;
 150         while (d->ofs < (ofs & (DIR_BUF_SIZE-1))) {
 151                 if (readdir(dir) == NULL) break;
 152         }
 153 #ifdef SEEKDIR_RETURNS_INT
 154         return -1;
 155 #endif
 156 }
 157
 158 void rewinddir(DIR *dir)
 159 {
 160         seekdir(dir, 0);
 161 }
 162
 163 int closedir(DIR *dir)
 164 {
 165         struct dir_buf *d = (struct dir_buf *)dir;
 166         int r = close(d->fd);
 167         if (r != 0) {
 168                 return r;
 169         }
 170         free(d);
 171         return 0;
 172 }
 173
 174 #ifndef dirfd
 175 /* darn, this is a macro on some systems. */
 176 int dirfd(DIR *dir)
 177 {
 178         struct dir_buf *d = (struct dir_buf *)dir;
 179         return d->fd;
 180 }
 181 #endif
 182
 183