#include <sys/mman.h>
#include <fcntl.h>
#include <unistd.h>
#include <err.h>
int
os_resize_anonymous_file(int fd, off_t size)
{
#ifdef HAVE_POSIX_FALLOCATE
/*
* Filesystems that do support fallocate will return EINVAL or
* EOPNOTSUPP. In this case we need to fall back to ftruncate
*/
errno = posix_fallocate(fd, 0, size);
if (errno == 0)
return 0;
else if (errno != EINVAL && errno != EOPNOTSUPP) {
warn("posix_fallocate failed");
return -1;
}
#endif
if (ftruncate(fd, size) < 0) {
warn("ftruncate failed");
return -1;
}
return 0;
}
int
main(void)
{
int fd;
off_t size = 12345;
fd = shm_open(SHM_ANON, O_CREAT | O_RDWR | O_CLOEXEC, 0600); // shm_open is always CLOEXEC
if (fd < 0)
err(1, "shm_open(SHM_ANON) failed");
if (os_resize_anonymous_file(fd, size) < 0) {
close(fd);
return -1;
}
return 0;
}