Date: Sun, 3 Dec 1995 14:58:40 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-hackers@freebsd.org, witr@rwwa.com Subject: Re: Proper way to determine non-blocking status... Message-ID: <199512030358.OAA07217@godzilla.zeta.org.au>
next in thread | raw e-mail | index | archive | help
>Even though it seems like it is almost never done by
>existing driver code, would I be correct in assuming that
>the *right* way to determine if a device read is allowed to
>sleep or not is the following?
>int xxread(dev_t dev, struct uio *uio, int ioflag)
>{
> if (ioflag & IO_NDELAY) {
> /* Can't block here */
> return EWOULDBLOCK;
> } else { /* Otherwise try again */
> /* Can sleep here */
> ...
> }
>}
Yes. See tty.c for examples. In open/ioctl/close you have to check
O_NONBLOCK (aka FNONBLOCK) instead of IO_NDELAY.
The ugl^H^H^Hrightly formatted way is:
int
xxread(dev, uio, ioflag)
dev_t dev;
struct uio *uio;
int ioflag;
{
/* Return early for nonblocking reads. */
if (ioflag & IO_NDELAY)
return (EWOULDBLOCK);
/* Can sleep here. */
...
}
Bruce
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?199512030358.OAA07217>