On Oct  9 08:31, Eric Blake wrote:
> On 10/09/2014 07:24 AM, corinna@cygwin.com wrote:
> 
> > Log message:
> > 	* fhandler_proc.cc (fhandler_proc::readdir): Set dirent d_type.
> > 	* fhandler_process.cc (fhandler_process::readdir): Ditto.
> > 	* fhandler_procnet.cc (fhandler_procnet::readdir): Ditto.
> > 	* fhandler_procsys.cc (fhandler_procsys::readdir): Ditto.
> > 	* fhandler_procsysvipc.cc (fhandler_procsysvipc::readdir): Ditto.
> > 	*  fhandler_virtual.h (virt_ftype_to_dtype): Define new inline function
> > 	to generate dirent d_type from virtual_ftype_t.
> 
> Most of these look okay; but I have a problem with fhandler_procsys.cc:
> 
> > @@ -357,10 +358,17 @@
> >  	res = ENMFILE;
> >        else
> >  	{
> > +	  struct stat st;
> > +	  char *file = tp.c_get ();
> > +
> >  	  sys_wcstombs (de->d_name, NAME_MAX + 1, f.dbi.ObjectName.Buffer,
> >  			f.dbi.ObjectName.Length / sizeof (WCHAR));
> >  	  de->d_ino = hash_path_name (get_ino (), de->d_name);
> > -	  de->d_type = 0;
> > +	  stpcpy (stpcpy (stpcpy (file, get_name ()), "/"), de->d_name);
> > +	  if (!lstat64 (file, &st))
> > +	    de->d_type = IFTODT (st.st_mode);
> > +	  else
> > +	    de->d_type = DT_UNKNOWN;
> 
> The whole point of d_type is for optimization, to tell a process when it
> can avoid the overhead of an lstat() because the system was able to
> obtain the information in a cheaper manner.  But if you have to resort
> to an lstat() to get the information, then you are wasting cycles on the
> case of a user that doesn't care about d_type.  I'd rather we always
> return DT_UNKNOWN if the only way we'd get a better type is by calling
> lstat().

I see.  The idea here was to try and, at least on my machine, it
was still *very* fast, likely because the whole thing occurs only
in globally allocated memory and there's no disk access or paging
involved.

The question is, what exactly do we lose?  /proc/sys isn't often
accessed at all (I guess) and what could be gained?  Yaakov asked
for setting d_type under /proc, so he might enlighten us which
tools make heavy use of the stuff, so the net gain is > 0...


Corinna

-- 
Corinna Vinschen                  Please, send mails regarding Cygwin to
Cygwin Maintainer                 cygwin AT cygwin DOT com
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