mkswap.c

   1 /*
   2
   3 Copyright (C) 2009 Rob Landley <rob@landley.net>
   4 Copyright (C) 2012 rofl0r
   5
   6 Permission to use, copy, modify, and/or distribute this software for any
   7 purpose with or without fee is hereby granted.
   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
  19 #include <stdlib.h>
  20 #include <unistd.h>
  21 #include <fcntl.h>
  22 #include <stdio.h>
  23 #include <sys/stat.h>
  24 #ifdef USE_LIBULZ
  25 #include <ulz/stdio-repl.h>
  26 #endif
  27
  28 #if !defined(_Noreturn) && __STDC_VERSION__+0 < 201112L
  29 #ifdef __GNUC__
  30 #define _Noreturn __attribute__((noreturn))
  31 #else
  32 #define _Noreturn
  33 #endif
  34 #endif
  35
  36 _Noreturn static void usage(void) {
  37         printf("usage: mkswap path-to-blockdevice\n");
  38         exit(1);
  39 }
  40
  41 _Noreturn static void die(const char* msg) {
  42         perror(msg);
  43         exit(1);
  44 }
  45
  46 #include <sys/ioctl.h>
  47 #include <sys/mount.h>
  48
  49 // Return how long the file at fd is, if there's any way to determine it.
  50 static off_t fdlength(int fd) {
  51         off_t bottom = 0, top = 0, pos, old;
  52         int size;
  53
  54         // If the ioctl works for this, return it.
  55
  56         if (ioctl(fd, BLKGETSIZE, &size) >= 0) return size*512L;
  57
  58         // If not, do a binary search for the last location we can read.  (Some
  59         // block devices don't do BLKGETSIZE right.)  This should probably have
  60         // a CONFIG option...
  61
  62         old = lseek(fd, 0, SEEK_CUR);
  63         do {
  64                 char temp;
  65
  66                 pos = bottom + (top - bottom) / 2;
  67
  68                 // If we can read from the current location, it's bigger.
  69
  70                 if (lseek(fd, pos, 0)>=0 && read(fd, &temp, 1)==1) {
  71                         if (bottom == top) bottom = top = (top+1) * 2;
  72                         else bottom = pos;
  73
  74                         // If we can't, it's smaller.
  75
  76                 } else {
  77                         if (bottom == top) {
  78                                 if (!top) return 0;
  79                                 bottom = top/2;
  80                         } else top = pos;
  81                 }
  82         } while (bottom + 1 != top);
  83
  84         lseek(fd, old, SEEK_SET);
  85
  86         return pos + 1;
  87 }
  88
  89 int main(int argc, char** argv) {
  90         int fd;
  91         if(argc != 2) usage();
  92         if ((fd  = open(argv[1], O_RDWR)) == -1) die("open");
  93
  94         size_t pagesize = sysconf(_SC_PAGE_SIZE);
  95         off_t len = fdlength(fd);
  96         if (len < (ssize_t) pagesize)
  97                 die("file to small");
  98
  99         size_t pages = (len/pagesize)-1;
 100         unsigned int swap[129] = {0};
 101
 102         // Write header.  Note that older kernel versions checked signature
 103         // on disk (not in cache) during swapon, so sync after writing.
 104
 105         swap[0] = 1;
 106         swap[1] = pages;
 107         lseek(fd, 1024, SEEK_SET);
 108         write(fd, swap, 129*sizeof(unsigned int));
 109         lseek(fd, pagesize-10, SEEK_SET);
 110         write(fd, "SWAPSPACE2", 10);
 111         fsync(fd);
 112
 113         close(fd);
 114
 115         printf("Swapspace size: %luk\n", pages*(unsigned long)(pagesize/1024));
 116         return 0;
 117 }