fileio.c

   1 /*
   2    Copyright (C) Andrew Tridgell 1998
   3    Copyright (C) 2002 by Martin Pool
   4
   5    This program is free software; you can redistribute it and/or modify
   6    it under the terms of the GNU General Public License as published by
   7    the Free Software Foundation; either version 2 of the License, or
   8    (at your option) any later version.
   9
  10    This program is distributed in the hope that it will be useful,
  11    but WITHOUT ANY WARRANTY; without even the implied warranty of
  12    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13    GNU General Public License for more details.
  14
  15    You should have received a copy of the GNU General Public License
  16    along with this program; if not, write to the Free Software
  17    Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  18 */
  19
  20 /*
  21   File IO utilities used in rsync
  22   */
  23 #include "rsync.h"
  24
  25 static char last_byte;
  26 static int last_sparse;
  27 extern int sparse_files;
  28
  29 int sparse_end(int f)
  30 {
  31         if (last_sparse) {
  32                 do_lseek(f,-1,SEEK_CUR);
  33                 return (write(f,&last_byte,1) == 1 ? 0 : -1);
  34         }
  35         last_sparse = 0;
  36         return 0;
  37 }
  38
  39
  40 static int write_sparse(int f,char *buf,size_t len)
  41 {
  42         size_t l1=0, l2=0;
  43         int ret;
  44
  45         for (l1=0;l1<len && buf[l1]==0;l1++) ;
  46         for (l2=0;l2<(len-l1) && buf[len-(l2+1)]==0;l2++) ;
  47
  48         last_byte = buf[len-1];
  49
  50         if (l1 == len || l2 > 0)
  51                 last_sparse=1;
  52
  53         if (l1 > 0) {
  54                 do_lseek(f,l1,SEEK_CUR);
  55         }
  56
  57         if (l1 == len)
  58                 return len;
  59
  60         ret = write(f, buf + l1, len - (l1+l2));
  61         if (ret == -1 || ret == 0)
  62                 return ret;
  63         else if (ret != (int) (len - (l1+l2)))
  64                 return (l1+ret);
  65
  66         if (l2 > 0)
  67                 do_lseek(f,l2,SEEK_CUR);
  68
  69         return len;
  70 }
  71
  72 /*
  73  * write_file does not allow incomplete writes.  It loops internally
  74  * until len bytes are written or errno is set.
  75  */
  76 int write_file(int f,char *buf,size_t len)
  77 {
  78         int ret = 0;
  79
  80         while (len>0) {
  81                 int r1;
  82                 if (sparse_files) {
  83                         int len1 = MIN(len, SPARSE_WRITE_SIZE);
  84                         r1 = write_sparse(f, buf, len1);
  85                 } else {
  86                         r1 = write(f, buf, len);
  87                 }
  88                 if (r1 <= 0) {
  89                         if (ret > 0) return ret;
  90                         return r1;
  91                 }
  92                 len -= r1;
  93                 buf += r1;
  94                 ret += r1;
  95         }
  96         return ret;
  97 }
  98
  99
 100
 101 /* this provides functionality somewhat similar to mmap() but using
 102    read(). It gives sliding window access to a file. mmap() is not
 103    used because of the possibility of another program (such as a
 104    mailer) truncating the file thus giving us a SIGBUS */
 105 struct map_struct *map_file(int fd,OFF_T len)
 106 {
 107         struct map_struct *map;
 108         map = (struct map_struct *)malloc(sizeof(*map));
 109         if (!map) out_of_memory("map_file");
 110
 111         map->fd = fd;
 112         map->file_size = len;
 113         map->p = NULL;
 114         map->p_size = 0;
 115         map->p_offset = 0;
 116         map->p_fd_offset = 0;
 117         map->p_len = 0;
 118
 119         return map;
 120 }
 121
 122 /* slide the read window in the file */
 123 char *map_ptr(struct map_struct *map,OFF_T offset,int len)
 124 {
 125         int nread;
 126         OFF_T window_start, read_start;
 127         int window_size, read_size, read_offset;
 128
 129         if (len == 0) {
 130                 return NULL;
 131         }
 132
 133         /* can't go beyond the end of file */
 134         if (len > (map->file_size - offset)) {
 135                 len = map->file_size - offset;
 136         }
 137
 138         /* in most cases the region will already be available */
 139         if (offset >= map->p_offset &&
 140             offset+len <= map->p_offset+map->p_len) {
 141                 return (map->p + (offset - map->p_offset));
 142         }
 143
 144
 145         /* nope, we are going to have to do a read. Work out our desired window */
 146         if (offset > 2*CHUNK_SIZE) {
 147                 window_start = offset - 2*CHUNK_SIZE;
 148                 window_start &= ~((OFF_T)(CHUNK_SIZE-1)); /* assumes power of 2 */
 149         } else {
 150                 window_start = 0;
 151         }
 152         window_size = MAX_MAP_SIZE;
 153         if (window_start + window_size > map->file_size) {
 154                 window_size = map->file_size - window_start;
 155         }
 156         if (offset + len > window_start + window_size) {
 157                 window_size = (offset+len) - window_start;
 158         }
 159
 160         /* make sure we have allocated enough memory for the window */
 161         if (window_size > map->p_size) {
 162                 map->p = (char *)Realloc(map->p, window_size);
 163                 if (!map->p) out_of_memory("map_ptr");
 164                 map->p_size = window_size;
 165         }
 166
 167         /* now try to avoid re-reading any bytes by reusing any bytes from the previous
 168            buffer. */
 169         if (window_start >= map->p_offset &&
 170             window_start < map->p_offset + map->p_len &&
 171             window_start + window_size >= map->p_offset + map->p_len) {
 172                 read_start = map->p_offset + map->p_len;
 173                 read_offset = read_start - window_start;
 174                 read_size = window_size - read_offset;
 175                 memmove(map->p, map->p + (map->p_len - read_offset), read_offset);
 176         } else {
 177                 read_start = window_start;
 178                 read_size = window_size;
 179                 read_offset = 0;
 180         }
 181
 182         if (read_size <= 0) {
 183                 rprintf(FINFO,"Warning: unexpected read size of %d in map_ptr\n", read_size);
 184         } else {
 185                 if (map->p_fd_offset != read_start) {
 186                         if (do_lseek(map->fd,read_start,SEEK_SET) != read_start) {
 187                                 rprintf(FERROR,"lseek failed in map_ptr\n");
 188                                 exit_cleanup(RERR_FILEIO);
 189                         }
 190                         map->p_fd_offset = read_start;
 191                 }
 192
 193                 if ((nread=read(map->fd,map->p + read_offset,read_size)) != read_size) {
 194                         if (nread < 0) nread = 0;
 195                         /* the best we can do is zero the buffer - the file
 196                            has changed mid transfer! */
 197                         memset(map->p+read_offset+nread, 0, read_size - nread);
 198                 }
 199                 map->p_fd_offset += nread;
 200         }
 201
 202         map->p_offset = window_start;
 203         map->p_len = window_size;
 204
 205         return map->p + (offset - map->p_offset);
 206 }
 207
 208
 209 void unmap_file(struct map_struct *map)
 210 {
 211         if (map->p) {
 212                 free(map->p);
 213                 map->p = NULL;
 214         }
 215         memset(map, 0, sizeof(*map));
 216         free(map);
 217 }
 218