Re: _IO_MTSAFE_IO

[Florian Weimer <fweimer at redhat dot com>]

On 04/29/2016 04:36 PM, Joseph Myers wrote:
> On Fri, 29 Apr 2016, Florian Weimer wrote:
>
> > Whether applications can use these macros is somewhat debatable, but as I
> > said, it happens within glibc as well.  There are repeated occurrences of this
>
> My view would be:
>
> * libio is not a public API for applications; only stdio is (and internals
> should be avoided in public headers where possible).  But ABI
> compatibility with old applications using libio may still be needed.

Yes, we need the ABI compatibility.  I believe some of the stdio macros 
need <libio.h> or something like it, too.

> * _IO_* symbols may be used internally in glibc for namespace reasons
> (where they are function aliases), or if there is another reason for using
> internals of another part of glibc.

Makes sense.

> > Curiously, _IO_flockfile and _IO_funlockfile are only defined in
> > libpthread.so, not in libc.so.  But these implementations are slightly
>
> They seem to be in the libc.abilist files to me....

Yes, I remembered incorrectly, I got a localplt failure during building. 
 So there currently aren't any _IO_flockfile references in libc.so, 
they are either expanded inline or they are elided.

I thought about the _IO_flockfile discrepancy some more.  I believe we 
should do the following:

(1) Replace _IO_flockfile references with a new internal function (say 
__flockfile_nouser).  This new function will perform the _IO_USER_LOCK 
check.

(2) Remove the symbols currently controlled by _IO_MTSAFE_IO from the 
API (header file at first, almost of _IO_* needs to be made compat-only, 
as you pointed out, but this is a different issue).

Florian