Re: Man page bugs?

[Jens Axboe <jens.axboe-QHcLZuEGTsvQT0dZR+AlfA@public.gmane.org>]

On Thu, Jan 31 2008, Michael Kerrisk wrote:
> 
> 
> Jens Axboe wrote:
> > On Thu, Jan 31 2008, Michael Kerrisk wrote:
> >> Hi Cong,
> >>
> >> WANG Cong wrote:
> >>> Hi, Michael and list!
> >>>
> >>> I found two problems in the man pages. The first one should
> >>> be a bug. It is that the type of the 2nd and 4th arguments
> >>> of splice(2) is wrong. The current prototype of splice(2)
> >>> in current man page is:
> >>>
> >>>        long splice(int fd_in, off_t *off_in, int fd_out,
> >>>                    off_t *off_out, size_t len, unsigned int flags);
> >>>
> >>> However, they should be 'loff_t' instead of 'off_t'. If we
> >>> use 'off_t', gcc will generate a warning. Patch is in the end
> >>> of this email and it's against 2.76 release. ;)
> >> Thanks for spotting that.  Fixed as you suggest, for man-pages-2.77.
> >>
> >>> The second one is a bit confused. The example given in tee(2)
> >>> even can not run normally. I got this error:
> >>>
> >>> $ ./example bar.txt
> >>> tee: Invalid argument
> >>>
> >>> I looked at tee(2), it is said that:
> >>>
> >>> EINVAL fd_in  or  fd_out  does not refer to a pipe; or fd_in and fd_out
> >>>        refer to the same pipe.
> >>>
> >>> So the first two arguments of tee(2) in the example is wrong,
> >>> since neither STDIN_FILENO nor STDOUT_FILENO refers to a pipe.
> >>> But I am not so sure, because I am new to tee(2). ;) If you can
> >>> comfirm this is really a bug, I can send a patch to fix this too.
> >>>
> >>> I have checked the newest release of man pages and my kernel version
> >>> is 2.6.21-1.3194.fc7. Did I miss something obvious?
> >> I'm not sure.  Perhaps Jens, the implementer of tee(2) can provide a little
> >> help.  Jens, what's an example of a command line for running the example
> >> program in the tee.2 man page?
> > 
> > It's not a bug, it should be run as:
> > 
> > $  echo hello | ./example output_file | cat
> > 
> > so that both stdin and stdout are pipes, as described in the man page.
> > The man page is correct.
> 
> Hi jens,
> 
> Yes, I guessed you probably should run it like that.  And it does produce
> the expected output on stdout.  However, the command then blocks, and if
> one types control-C, the output_file is empty.  How should this program be
> terminated so that something does end up in the output_file?

See ktee.c from the splice sample repo, it works correctly:

axboe@carl:~/git/splice> echo hello | ./ktee outfile | cat
hello
axboe@carl:~/git/splice> cat outfile 
hello

I don't have the tee(2) man page here so can't verify, but try and
compare them!

-- 
Jens Axboe