From mboxrd@z Thu Jan  1 00:00:00 1970
From: Pat LaVarre <p.lavarre@ieee.org>
Subject: Re: sg utils sg_io -i 0x24 -y "12 00:00:00 24 00"
Date: 02 Dec 2003 17:17:56 -0700
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> > - O_RDWR
> > + O_RDONLY|O_NONBLOCK
> ...
> I dreamed up this patch only by guessing from
> hints found on the web, not from reading a
> document anywhere.

Possibly we recommend open O_NONBLOCK for SG_IO.

Evidence in favour of that conjecture includes the following, not close
to block/scsi_ioctl.c in the kernel source, but yes close in author
space:

---

From: linux-2.6.0-test11/Documentation/cdrom/cdrom-standard.tex
...
1997/12/28 ...
...
We therefore propose to use the flag $O_NONBLOCK$ to indicate
that the device is opened just for issuing $ioctl$
commands. Strictly, the meaning of $O_NONBLOCK$ is that opening and
subsequent calls to the device don't cause the calling process to
wait. We could interpret this as ``don't wait until someone has
inserted some valid data-\cdrom.'' Thus, our proposal of the
implementation for the $open()$ call for \cdrom s is:
...
\begin{itemize}
...
\item If no other flags are set than $O_RDONLY$, the device is opened
for data transfer, and the return value will be 0 only upon successful
initialization of the transfer. The call may even induce some actions
on the \cdrom, such as closing the tray.
...
\item If the option flag $O_NONBLOCK$ is set, opening will always be
successful, unless the whole device doesn't exist. The drive will take
no actions whatsoever.
...
\end{itemize}

---

Pat LaVarre