Proposal: Replace xstat (stat version dispatcher)

[Florian Weimer]

We currently have this (in <sys/stat.h>)

/* To allow the `struct stat' structure and the file type `mode_t'
   bits to vary without changing shared library major version number,
   the `stat' family of functions and `mknod' are in fact inline
   wrappers around calls to `xstat', `fxstat', `lxstat', and `xmknod',
   which all take a leading version-number argument designating the
   data structure and bits used.  <bits/stat.h> defines _STAT_VER with
   the version number corresponding to `struct stat' as defined in
   that file; and _MKNOD_VER with the version number corresponding to
   the S_IF* macros defined therein.  It is arranged that when not
   inlined these function are always statically linked; that way a
   dynamically-linked executable always encodes the version number
   corresponding to the data structures it uses, so the `x' functions
   in the shared library can adapt without needing to recompile all
   callers.  */

and (in io/stat.c):

/* This definition is only used if inlining fails for this function; see
   the last page of <sys/stat.h>.  The real work is done by the `x'
   function which is passed a version number argument.  We arrange in the
   makefile that when not inlined this function is always statically
   linked; that way a dynamically-linked executable always encodes the
   version number corresponding to the data structures it uses, so the `x'
   functions in the shared library can adapt without needing to recompile
   all callers.  */

Should we switch this over to symbol versioning, with definitions for
the stat, fstat, &c functions in libc.so.6?

Thanks,
Florian