[lkml]   [2001]   [Jan]   [12]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
Messages in this thread
SubjectRe: O_NONBLOCK, read(), select(), NFS, Ext2, etc.
On Fri, Jan 12, 2001 at 09:40:55AM +0000, Alan Cox wrote:
> > 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

I have a long standing idea on modifying poll/read/write behavior on
regular files opened in O_NONBLOCK mode. How about the following scheme:

* poll returns POLLIN/POLLOUT on regular files only if the data are
in buffer cache/there is room for write().
* read returns EAGAIN if the data are not in buffer cache.
* write returns EAGAIN if there is no room (yet) to store the data.

All the operation should signal to IO subsystem that the data are
needed in cache/the room has to be freed.

To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to
Please read the FAQ at

 \ /
  Last update: 2005-03-22 13:28    [W:0.086 / U:0.596 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site