From: Corinna Vinschen <corinna-cygwin@cygwin.com>
To: cygwin-developers@cygwin.com
Subject: Re: src/winsup/cygwin ChangeLog fhandler_proc.cc f ...
Date: Thu, 09 Oct 2014 14:51:00 -0000 [thread overview]
Message-ID: <20141009145128.GA25442@calimero.vinschen.de> (raw)
In-Reply-To: <54369C4E.2030708@redhat.com>
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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
Red Hat
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next prev parent reply other threads:[~2014-10-09 14:51 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20141009132437.7650.qmail@sourceware.org>
2014-10-09 14:31 ` Eric Blake
2014-10-09 14:51 ` Corinna Vinschen [this message]
2014-10-09 15:07 ` Eric Blake
2014-10-09 16:22 ` Corinna Vinschen
2014-10-09 17:47 ` Corinna Vinschen
2014-10-09 18:07 ` Eric Blake
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