Date: Mon, 1 Aug 2005 15:05:02 +0200 From: Marc Olzheim <marcolz@stack.nl> To: soc-victor@freebsd.org Cc: freebsd-hackers@freebsd.org Subject: Re: O_NONBLOCK for devices with removable media Message-ID: <20050801130502.GA39470@stack.nl> In-Reply-To: <494025505080104427c3f91f6@mail.gmail.com> References: <494025505080104427c3f91f6@mail.gmail.com>
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--y0ulUmNC+osPPQO6 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Mon, Aug 01, 2005 at 02:42:21PM +0300, victor cruceru wrote: > Hi all, > I'm just wondering if it's OK for an open syscall on such a device (i.e.= =20 > /dev/acd0 or /dev/da1 with a CF reader attached) to block till the media = is=20 > ready or a timeout occurs. I'd say that depends completely on whether you supply O_NONBLOCK or not, so yes. Quoted from a sound driver discussion at:=20 http://sourceforge.net/mailarchive/message.php?msg_id=3D10011826 On block devices, O_NONBLOCK also is a way to say "don't try to do any=20 device discovery", ie you can do a O_NONBLOCK open on a removable disk=20 that doesn"t even have any media in it. Again, this has _nothing_ to do=20 with whether the device is "busy" or not. =2E.. Short summary: =20 - O_NONBLOCK should generally be seen as just setting the O_NONBLOCK flag= =20 "early" (ie it"s conceptually equivalent to doing a "F_SETFL" fcntl=20 before the open. It _may_ affect the open itself, but when it does, it= =20 is generally considered to mean that you can open something that isn't= =20 even _reachable_. =20 - POSIX doesn't say anything much about its behaviour, except for named= =20 pipes, where it says the total reverse of what ALSA does. But that=20 doesn't actually mean anything, because even that is very much defined= =20 as a special case by POSIX. Marc --y0ulUmNC+osPPQO6 Content-Type: application/pgp-signature Content-Disposition: inline -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.1 (FreeBSD) iD8DBQFC7h3+ezjnobFOgrERAtlKAJwOytkg9PPLqeIXJ6TmSFDwrZRiEwCgynB8 JTtEaJ3En4jNvgYdnKYCN1Q= =Rrpr -----END PGP SIGNATURE----- --y0ulUmNC+osPPQO6--
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