lib/replace/repdir_getdents.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 systems
  25
  26   This is needed because the existing directory handling in FreeBSD
  27   and OpenBSD (and possibly NetBSD) doesn't correctly handle unlink()
  28   on files in a directory where telldir() has been used. On a block
  29   boundary it will occasionally miss a file when seekdir() is used to
  30   return to a position previously recorded with telldir().
  31
  32   This also fixes a severe performance and memory usage problem with
  33   telldir() on BSD systems. Each call to telldir() in BSD adds an
  34   entry to a linked list, and those entries are cleaned up on
  35   closedir(). This means with a large directory closedir() can take an
  36   arbitrary amount of time, causing network timeouts as millions of
  37   telldir() entries are freed
  38
  39   Note! This replacement code is not portable. It relies on getdents()
  40   always leaving the file descriptor at a seek offset that is a
  41   multiple of DIR_BUF_SIZE. If the code detects that this doesn't
  42   happen then it will abort(). It also does not handle directories
  43   with offsets larger than can be stored in a long,
  44
  45   This code is available under other free software licenses as
  46   well. Contact the author.
  47 */
  48
  49 #include <stdlib.h>
  50 #include <sys/stat.h>
  51 #include <unistd.h>
  52 #include <sys/types.h>
  53 #include <errno.h>
  54 #include <fcntl.h>
  55 #include <dirent.h>
  56
  57 #define DIR_BUF_BITS 9
  58 #define DIR_BUF_SIZE (1<<DIR_BUF_BITS)
  59
  60 struct dir_buf {
  61         int fd;
  62         int nbytes, ofs;
  63         off_t seekpos;
  64         char buf[DIR_BUF_SIZE];
  65 };
  66
  67 DIR *opendir(const char *dname)
  68 {
  69         struct dir_buf *d;
  70         struct stat sb;
  71         d = malloc(sizeof(*d));
  72         if (d == NULL) {
  73                 errno = ENOMEM;
  74                 return NULL;
  75         }
  76         d->fd = open(dname, O_RDONLY);
  77         if (d->fd == -1) {
  78                 free(d);
  79                 return NULL;
  80         }
  81         if (fstat(d->fd, &sb) < 0) {
  82                 close(d->fd);
  83                 free(d);
  84                 return NULL;
  85         }
  86         if (!S_ISDIR(sb.st_mode)) {
  87                 close(d->fd);
  88                 free(d);
  89                 errno = ENOTDIR;
  90                 return NULL;
  91         }
  92         d->ofs = 0;
  93         d->seekpos = 0;
  94         d->nbytes = 0;
  95         return (DIR *)d;
  96 }
  97
  98 struct dirent *readdir(DIR *dir)
  99 {
 100         struct dir_buf *d = (struct dir_buf *)dir;
 101         struct dirent *de;
 102
 103         if (d->ofs >= d->nbytes) {
 104                 d->seekpos = lseek(d->fd, 0, SEEK_CUR);
 105                 d->nbytes = getdents(d->fd, d->buf, DIR_BUF_SIZE);
 106                 d->ofs = 0;
 107         }
 108         if (d->ofs >= d->nbytes) {
 109                 return NULL;
 110         }
 111         de = (struct dirent *)&d->buf[d->ofs];
 112         d->ofs += de->d_reclen;
 113         return de;
 114 }
 115
 116 long telldir(DIR *dir)
 117 {
 118         struct dir_buf *d = (struct dir_buf *)dir;
 119         if (d->ofs >= d->nbytes) {
 120                 d->seekpos = lseek(d->fd, 0, SEEK_CUR);
 121                 d->ofs = 0;
 122                 d->nbytes = 0;
 123         }
 124         /* this relies on seekpos always being a multiple of
 125            DIR_BUF_SIZE. Is that always true on BSD systems? */
 126         if (d->seekpos & (DIR_BUF_SIZE-1)) {
 127                 abort();
 128         }
 129         return d->seekpos + d->ofs;
 130 }
 131
 132 void seekdir(DIR *dir, long ofs)
 133 {
 134         struct dir_buf *d = (struct dir_buf *)dir;
 135         d->seekpos = lseek(d->fd, ofs & ~(DIR_BUF_SIZE-1), SEEK_SET);
 136         d->nbytes = getdents(d->fd, d->buf, DIR_BUF_SIZE);
 137         d->ofs = 0;
 138         while (d->ofs < (ofs & (DIR_BUF_SIZE-1))) {
 139                 if (readdir(dir) == NULL) break;
 140         }
 141 }
 142
 143 void rewinddir(DIR *dir)
 144 {
 145         seekdir(dir, 0);
 146 }
 147
 148 int closedir(DIR *dir)
 149 {
 150         struct dir_buf *d = (struct dir_buf *)dir;
 151         int r = close(d->fd);
 152         if (r != 0) {
 153                 return r;
 154         }
 155         free(d);
 156         return 0;
 157 }
 158
 159 #ifndef dirfd
 160 /* darn, this is a macro on some systems. */
 161 int dirfd(DIR *dir)
 162 {
 163         struct dir_buf *d = (struct dir_buf *)dir;
 164         return d->fd;
 165 }
 166 #endif