Messages in this thread | | | Date | Mon, 15 Feb 2010 09:50:22 -0800 (PST) | From | Davide Libenzi <> | Subject | Re: [patch/rfc] Make poll/select report error (POLLNVAL and EBADF) for unsupported files |
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On Mon, 15 Feb 2010, Eric Dumazet wrote:
> Le dimanche 14 février 2010 à 14:27 -0800, Davide Libenzi a écrit : > > Currently poll and select consider a non poll-supported file as one with > > full event mask set, instead of reporting proper error to the caller. > > This behavior can fool the caller of proper functionality being returned, > > while instead no valid event was processed/read from the device. > > This came out linked to this bug report: > > > > http://bugzilla.kernel.org/show_bug.cgi?id=15272 > > > > IMHO, it'd be more adequate to report proper error code, for files that do > > not support f_op->poll(), but then I am also not sure how much breakage > > can this bring to existing (already broken "in just the right way") > > applications. > > Untested, discussion-only, patch. > > > > > > Signed-off-by: Davide Libenzi <davidel@xmailserver.org> > > > > > > - Davide > > Hmm, according to POSIX : > > The poll() function shall support regular files, terminal and > pseudo-terminal devices, FIFOs, pipes, sockets ... > > Regular files shall always poll TRUE for reading and writing. > > > So unless I missed something, this patch could break some conformant > applications.
If that's POSIX, than the patch is no good. I missed the part on the regular files being always ready, which explaqins why the code is as it is right now.
> In particular, if an application is polling() on stdin (usually a tty), > and other 'files', what's happening if we do : > > cat replay_file | application > > Either it wont read stdin, or application exits without reading its > input.
That case would be fine, since that's a pipe. This will behave differently:
$ application < replay_file
Anyway, since POSIX states the above, the patch cannot apply.
- Davide
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