At some point during my C programming adventures on Linux, I encountered flags (possibly ioctl/fcntl?), that make reads and writes on a file descriptor uninterruptible.
Unfortunately I cannot recall how to do this, or where I read it. Can anyone shed some light?
To refine my query, I'm after the same blocking and guarantees that fwrite() and fread() provide, sans userspace buffering.
You can avoid EINTR from read() and write() by ensuring all your signal handlers are installed with the SA_RESTART flag of sigaction().
However this does not protect you from short reads / writes. This is only possible by putting the read() / write() into a loop (it does not require an additional buffer beyond the one that must already be supplied to the read() / write() call.)
Such a loop would look like:
/* If return value is less than `count', then errno == 0 indicates end of file,
* otherwise errno indicates the error that occurred. */
ssize_t hard_read(int fd, void *buf, size_t count)
{
ssize_t rv;
ssize_t total_read = 0;
while (total_read < count)
{
rv = read(fd, (char *)buf + total_read, count - total_read);
if (rv == 0)
errno = 0;
if (rv < 1)
if (errno == EINTR)
continue;
else
break;
total_read += rv;
}
return rv;
}