Re: O_NONBLOCK, read(), select(), NFS, Ext2, etc.

From: Alan Cox (alan@lxorguk.ukuu.org.uk)
Date: Fri Jan 12 2001 - 04:40:55 EST

> using the O_NONBLOCK flag, then read() and write() will always return
> immediately and not block the calling process. This does not appear to
> be true; but perhaps I am doing something wrong. If I open() a file (on
> 2.2.18) from a floppy or NFS mount (to test in a slow environment) with
> O_NONBLOCK|O_RDONLY, read() will still block. If I try to select() on
> the file descriptor, select() always returns 0.

The definition of immediate is not 'instant'. Otherwise no I/O system would
ever return anything but -EWOULDBLOCK. Its that it won't wait when there is
no data pending. On a floppy there is always data pending

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