[Bug libc/14433] New: setvbuf _IOLBF doesn't honor size

["P at draigBrady dot com" <sourceware-bugzilla at sourceware dot org>]

http://sourceware.org/bugzilla/show_bug.cgi?id=14433

             Bug #: 14433
           Summary: setvbuf _IOLBF doesn't honor size
           Product: glibc
           Version: 2.14
            Status: NEW
          Severity: normal
          Priority: P2
         Component: libc
        AssignedTo: unassigned@sourceware.org
        ReportedBy: P@draigBrady.com
                CC: drepper.fsp@gmail.com
    Classification: Unclassified


POSIX says _IOLBF shall enable line buffering.
However there are two aspects to line buffering.

1. Atomic output of lines, so they're not split
2. Immediate output of lines.

Currently _IOLBF does both of the above.
I would like to propose a change so that if size is specified with _IOLBF,
then 2. is not done, and instead output is only done when the buffer is full.
This would allow programs to distinguish their requirements and improve
performance.

For example, the GNU coreutils checksum utilities would like
behavior 1 above, but not 2, so that output is generated efficiently,
when many small files are being processed.

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