Tail not reading to end of input

[smr xxxx]

I've done some debugging of tail.exe on XP (which works) and Vista
Enterprise SP1 (which doesn't), and so far have found two differences
when tailing output piped from another program:
  1. S_ISREG (stats.st_mode) returns 0 on XP, but 1 on Vista (I
haven't yet determined if this is an Enterprise-only or an SP1-only
issue)
  2. lseek() fails on XP, but succeeds on Vista.  The SEEK_CUR below
returns 0, and the SEEK_END consistently returns 4105 in my tests (for
output that should be much longer, so presumably it's looking at a
single buffer of data).
Combines, this means that on XP the following code in tail.c results
in pipe_lines being called (as expected), but on Vista file_lines is
being called.  Does any of this mean anything to anyone?

      /* Use file_lines only if FD refers to a regular file for
	 which lseek (... SEEK_END) works.  */
      if ( ! presume_input_pipe
	   && S_ISREG (stats.st_mode)
	   && (start_pos = lseek (fd, 0, SEEK_CUR)) != -1
	   && start_pos < (end_pos = lseek (fd, 0, SEEK_END)))
	{
                          file_lines(...);
                }
                else
                {
                          pipe_line(...);
                }


On Mon, Apr 14, 2008 at 10:56 AM, smr xxxx <smrxxxx@gmail.com> wrote:
> Hi, I've just rebuilt my machine and done a clean install of the
> latest Cygwin, and am having a problem with tail.  I'm wanting to know
> whether this is a known issue before digging deeper.  For other
> reasons, I've rebuilt my machine clean twice this weekend and have had
> this problem both times -- I also sourced the Cygwin files from two
> different mirrors.
>
> It's been a few months since I last installed Cygwin, and all I can
> think of that has changed since then is:
>  1. I have a newer version of Cygwin
>  2. I'm now on Vista Enterprise (was Vista Ultimate)
>  3. I'm now on an SP1 of Vista (was original RTM of Vista)
>
> When running a command such as "dir /s /a cygwin | tail -2" (from C:\)
> it displays:
>  03/04/2008  10:32 PM                35 7zr
>  07/19/2007  02:05 PM
> This last line is the 29th line of output.  Redirecting to a file
> shows that there are 7 spaces at the end of this last line, and the
> total output is 1028 bytes, or 1000 after running dos2unix.
>
> Moving C:\cygwin to C:\x\cygwin (to force some extra characters into
> the output of the above command, ie. the "x\") and rerunning shows
> that it again stops at precisely the same place (7 spaces after the
> time on the 29th line), but the output is now 1032 bytes, or 1004
> after running dos2unix, due to the extra characters.
>
> If I first redirect the output of the dir command to a file and tail
> that then all is well.  Even running "type filename | tail -2" works.
> Also, if I dos2unix the stream inplace (ie. "dir /s /a cygwin |
> dos2unix | tail -2") it works correctly.  Note that I installed with
> Unix file type (as always).
>
> I just tried the same on \Windows, and it stops on the 26th line at a
> position that seems to amount to 1124 bytes, or 1098 when dos2unix'd.
>
> I'm guessing that this is a bigger problem that just tail (I could be
> wrong), but "dir /s /a cygwin | wc -l" doesn't have any problems.
>
> Has anyone seen this before?
>

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