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Re: Bug#545422: coreutils: "tail -f -" fails

From: Jim Meyering
Subject: Re: Bug#545422: coreutils: "tail -f -" fails
Date: Tue, 22 Sep 2009 21:32:27 +0200

Giuseppe Scrivano wrote:
> have you considered this patch for inclusion?  I don't see a clearer way
> to avoid polling without inotify fd support.

>> This patch changes `tail' to handle stdin separately from inotify
>> events, similar to what we are already doing when a --pid is specified.

Hi Giuseppe,

Considering the amount of complexity it adds to already-dense code
(in spite of the fact that some is just due to indentation changes),
for so little gain (who will use tail -f on stdin and care whether tail
is sleep-based or inotify-based?), I'm reluctant to use it at all.

Is there a good reason to want to avoid the sleep-based code
in this corner case?

> Subject: [PATCH] tail: handle "-" properly
> * src/tail.c (tail_forever_inotify): Handle stdin (i.e., "-", but not
> /dev/stdin) separately from inotify.
> * tests/tail-2/wait: Ensure that when a stdin is watched, tail does not
> raise errors.

BTW, that log message is out of date.
tail -f handles "-" now, via the sleep-based implementation.

Summarizing what this patch does: it changes e.g., tail -f - F1 F2 F3
not to revert to the sleep-based implementation solely due
to the presence of an unnamed (stdin) file, "-".
Instead, the files F1, F2, F3 would still be tracked efficiently via
inotify, and stdin would be tracked via a select-based wait.

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