Re: [PATCH] tee: Add --pipe-check to allow instantly detecting closed outputs

[Carl Edquist]

On Fri, 9 Dec 2022, Carl Edquist wrote:

> On Fri, 9 Dec 2022, Arsen Arsenović wrote:
>
> > > ... Also, i suspect that the pipe_check option can be disabled if the 
> > > _input_ is a regular file (or block device), since (i think) these 
> > > always show up as ready for reading.  (This check would only need to 
> > > be done once for fd 0 at program start.)
> >
> > Yes, there's no point poll-driving those, since it'll be always 
> > readable, up to EOF, and never hesitate to bring more data.  It might 
> > just end up being a no-op if used in current form (but I haven't 
> > tried).
>
> Well currently if the input is a regular file, poll() immediately 
> returns POLLIN, along with any potential errors for the output.  But yes 
> the net effective behavior is the same as if the poll() call had been 
> skipped.

In a way i don't think it's so necessary (as it's just an optimization, 
and it's only relevant if the user calls tee with -P/--pipe-check despite 
stdin being a regular file or block device), but anyway my attached patch 
(0002-tee-skip-pipe-checks-if-input-is-always-ready-for-re.patch) adds 
logic to disable pipe_check mode in this case.  (Though in order not to 
change the SIGPIPE semantics, -P still implies -p.)


Carl

0001-tee-only-fstat-outputs-if-pipe_check-is-active.patch
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0002-tee-skip-pipe-checks-if-input-is-always-ready-for-re.patch
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