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

[Michael Rothwell]

Alan Cox wrote:
> 
> > 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

How about using fcntl(), O_ASYNC and SIGIO? Or maybe a broader question:
what's the preferred/working way to do async file i/o on Linux?

-M