利用mmap实现文件拷贝功能

/*  * gcc -Wall -O3 -o copy_mmap copy_mmap.c */ #include < stdio.h > #include < stdlib.h > #include < string .h > /* for memcpy */ #include < strings.h > #include < sys / mman.h > #include < sys / types.h > #include < sys / stat.h > #include < fcntl.h > #include < unistd.h > #define PERMS 0600 int main ( int argc, char * argv[] ){  int   src, dst;  void   * sm, * dm;   struct stat statbuf;  if ( argc != 3 ) {  fprintf( stderr, " Usage: %s /n " , argv[ 0 ] );  exit( EXIT_FAILURE ); }  if ( ( src = open( argv[ 1 ], O_RDONLY ) ) < 0 ) {  perror( " open source " );  exit( EXIT_FAILURE ); }  /* 为了完成复制，必须包含读打开，否则mmap()失败 */   if ( ( dst = open( argv[ 2 ], O_RDWR | O_CREAT | O_TRUNC, PERMS ) ) < 0 ) {  perror( " open target " );  exit( EXIT_FAILURE ); }  if ( fstat( src, & statbuf ) < 0 ) {  perror( " fstat source " );  exit( EXIT_FAILURE ); }  /*   * 参看前面man手册中的说明，mmap()不能用于扩展文件长度。所以这里必须事  * 先扩大目标文件长度，准备一个空架子等待复制。  */   if ( lseek( dst, statbuf.st_size - 1 , SEEK_SET ) < 0 ) {  perror( " lseek target " );  exit( EXIT_FAILURE );  }   if ( write( dst, & statbuf, 1 ) != 1 ) {  perror( " write target " );  exit( EXIT_FAILURE ); }    /* 读的时候指定 MAP_PRIVATE 即可 */  sm = mmap( 0 , ( size_t )statbuf.st_size, PROT_READ,    MAP_PRIVATE | MAP_NORESERVE, src, 0 );  if ( MAP_FAILED == sm ) {  perror( " mmap source " );  exit( EXIT_FAILURE ); }  /* 这里必须指定 MAP_SHARED 才可能真正改变静态文件 */  dm = mmap( 0 , ( size_t )statbuf.st_size, PROT_WRITE,    MAP_SHARED, dst, 0 );  if ( MAP_FAILED == dm ) {  perror( " mmap target " );  exit( EXIT_FAILURE ); } memcpy( dm, sm, ( size_t )statbuf.st_size );  /*   * 可以不要这行代码  *  * msync( dm, ( size_t )statbuf.st_size, MS_SYNC );  */   return ( EXIT_SUCCESS );}