* [Bug 91931] New: fflush(3) is misleading about input streams
@ 2015-01-23 16:15 bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
[not found] ` <bug-91931-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/>
0 siblings, 1 reply; 5+ messages in thread
From: bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r @ 2015-01-23 16:15 UTC (permalink / raw)
To: linux-man-u79uwXL29TY76Z2rM5mHXA
https://bugzilla.kernel.org/show_bug.cgi?id=91931
Bug ID: 91931
Summary: fflush(3) is misleading about input streams
Product: Documentation
Version: unspecified
Hardware: All
OS: Linux
Status: NEW
Severity: normal
Priority: P1
Component: man-pages
Assignee: documentation_man-pages-ztI5WcYan/vQLgFONoPN62D2FQJk+8+b@public.gmane.org
Reporter: cubbi-+Aw+eGX9mmUAvxtiuMwx3w@public.gmane.org
Regression: No
Current fflush(3) claims that
"For input streams, fflush() discards any buffered data that has been fetched
from the underlying file, but has not been consumed by the application."
While technically true (assuming 'file' implies seekable device), this is
incomplete: flushing an input stream associated with a non-seekable device,
such as the terminal input, does nothing (the update to fp->_IO_read_end at
libio/fileops.c:872 does not happen due to ESPIPE from lseek)
There have been enough confused beginner posts to various internet forums
asking why flushing stdin doesn't work on Linux. I believe it is worth making
the man page more explicit. At the very least, it should begin that sentence
with "For input streams associated with seekable devices", or perhaps it should
mention the unfortunately popular use case fflush(stdin) explicitly.
On a very minor note, fflush(3) also claims that
"The standards do not specify the behavior for input streams"
This is no longer precisely correct; POSIX specifies behavior for seekable
input streams to move fileno's offset to match FILE's offset and undo all
ungetc's: http://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html
and glibc conforms to that (or tries to,
https://sourceware.org/bugzilla/show_bug.cgi?id=5994 is still open)
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^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug 91931] fflush(3) is misleading about input streams
[not found] ` <bug-91931-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/>
@ 2015-01-25 19:53 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-27 4:35 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r @ 2015-01-25 19:53 UTC (permalink / raw)
To: linux-man-u79uwXL29TY76Z2rM5mHXA
https://bugzilla.kernel.org/show_bug.cgi?id=91931
Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org
--- Comment #1 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
Thanks for the report. I think you are more or less right. One question though:
should the text not be in terms of "block buffered stream" rather than
"seekable device"?
Thanks,
Michael
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^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug 91931] fflush(3) is misleading about input streams
[not found] ` <bug-91931-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/>
2015-01-25 19:53 ` [Bug 91931] " bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
@ 2015-01-27 4:35 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-28 8:31 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-28 8:33 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
3 siblings, 0 replies; 5+ messages in thread
From: bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r @ 2015-01-27 4:35 UTC (permalink / raw)
To: linux-man-u79uwXL29TY76Z2rM5mHXA
https://bugzilla.kernel.org/show_bug.cgi?id=91931
--- Comment #2 from cubbi-+Aw+eGX9mmUAvxtiuMwx3w@public.gmane.org ---
I don't see how buffering strategy would be relevant: it calls lseek(2) the
same way whether the streams are setvbuf'd line-buffered or block-buffered.
POSIX wording is simply "the file is one capable of seeking"
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^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug 91931] fflush(3) is misleading about input streams
[not found] ` <bug-91931-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/>
2015-01-25 19:53 ` [Bug 91931] " bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-27 4:35 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
@ 2015-01-28 8:31 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-28 8:33 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
3 siblings, 0 replies; 5+ messages in thread
From: bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r @ 2015-01-28 8:31 UTC (permalink / raw)
To: linux-man-u79uwXL29TY76Z2rM5mHXA
https://bugzilla.kernel.org/show_bug.cgi?id=91931
--- Comment #3 from Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> ---
(In reply to cubbi from comment #0)
> On a very minor note, fflush(3) also claims that
> "The standards do not specify the behavior for input streams"
>
> This is no longer precisely correct; POSIX specifies behavior for seekable
> input streams to move fileno's offset to match FILE's offset and undo all
> ungetc's:
> http://pubs.opengroup.org/onlinepubs/9699919799/functions/fflush.html and
> glibc conforms to that (or tries to,
> https://sourceware.org/bugzilla/show_bug.cgi?id=5994 is still open)
Thanks. I modified the text to note that POSIX.1-2008 does add specification
for input streams.
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^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug 91931] fflush(3) is misleading about input streams
[not found] ` <bug-91931-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/>
` (2 preceding siblings ...)
2015-01-28 8:31 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
@ 2015-01-28 8:33 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
3 siblings, 0 replies; 5+ messages in thread
From: bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r @ 2015-01-28 8:33 UTC (permalink / raw)
To: linux-man-u79uwXL29TY76Z2rM5mHXA
https://bugzilla.kernel.org/show_bug.cgi?id=91931
Michael Kerrisk <mtk.manpages-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |RESOLVED
Resolution|--- |CODE_FIX
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2015-01-23 16:15 [Bug 91931] New: fflush(3) is misleading about input streams bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
[not found] ` <bug-91931-11311-3bo0kxnWaOQUvHkbgXJLS5sdmw4N0Rt+2LY78lusg7I@public.gmane.org/>
2015-01-25 19:53 ` [Bug 91931] " bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-27 4:35 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
2015-01-28 8:31 ` bugzilla-daemon-590EEB7GvNiWaY/ihj7yzEB+6BGkLq7r
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