Corinna Vinschen wrote:
> mmap always allocates in 64K chunks.
That doesn't seem to be true in practice. In the test below I mmap a
1080K file (this is a multiple of 4K but not a multiple of 64K). The
first byte after the end of the file isn't readable.
$ cat mmaptest.c
#include <fcntl.h>
#include <stdio.h>
#include <sys/mman.h>
#include <sys/stat.h>
int main(int argc, char *argv[])
{
int fd;
struct stat st;
void *p;
if (argc != 2) return 1;
if ((fd = open(argv[1], O_RDONLY, 0)) < 0) return 1;
if (fstat(fd, &st) != 0) return 1;
if ((p = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, fd,
0)) == MAP_FAILED) return 1;
printf("last byte 0x%02X\n", ((unsigned char *)p)[st.st_size - 1]);
fflush(stdout);
printf("next byte 0x%02X\n", ((unsigned char *)p)[st.st_size]);
return 0;
}
$ gcc -o mmaptest mmaptest.c
$ dd bs=1080K count=1 if=/dev/random of=foo
1+0 records in
1+0 records out
1105920 bytes (1.1 MB) copied, 0.077 s, 14.4 MB/s
$ ./mmaptest foo
last byte 0x5F
9 [main] mmaptest 3040 _cygtls::handle_exceptions: Error while dumping sta
te (probably corrupted stack)
Segmentation fault (core dumped)
This is a recent cygwin installation on XP Pro SP2.
Thanks,
Jay.
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