From: Corinna Vinschen <corinna-cygwin@cygwin.com>
Subject: Re: New platform independent problem
Date: Fri, 20 Jan 2006 15:14:12 +0100 [thread overview]
Message-ID: <20060120141412.GA11284@calimero.vinschen.de> (raw)
In-Reply-To: <43D0ECA5.3030506@byu.net>
[Resent to add emacs-devel and Eli on the "To:" list]
On Jan 20 06:59, Eric Blake wrote:
> According to Corinna Vinschen on 1/20/2006 5:25 AM:
> > I'm also having a problem right now building rcp and scp due to the
> > missing d_ino. OTOH, the d_ino member is not required by POSIX, but
> > only in X/Open compliant OSes, see
> >
> > http://www.opengroup.org/onlinepubs/009695399/basedefs/dirent.h.html
> > http://www.opengroup.org/onlinepubs/009695399/basedefs/xbd_chap02.html#tag_02_01_04
> >
> > So, portable applications shouldn't rely on d_ino.
>
> Is there a compromise here? Many applications that look at d_ino also
> check whether the d_ino member is 0, in which case they fall back on
> st_ino. For example, coreutils's pwd.c contains:
>
> #define NOT_AN_INODE_NUMBER 0
> #ifdef D_INO_IN_DIRENT
> # define D_INO(dp)((dp)->d_ino)
> #else
> /* Some systems don't have inodes, so fake them to avoid lots of ifdefs. */
> # define D_INO(dp) NOT_AN_INODE_NUMBER
> #endif
>
> Then later on, it can blindly do:
>
> ino_t ino = D_INO(dp);
> if (ino == NOT_AN_INODE_NUMBER)
> {
> if (lstat (dp->d_name, &ent_sb) < 0)
> continue; /* Skip any entry we can't stat. */
> ino = ent_sb.st_ino;
> }
Well, other applications like rcp and scp just use d_ino to check for 0
and to ignore it entirely then, like this:
while (readdir)
{
if (d_ino == 0)
continue;
[...action...]
}
This means, if d_ino is 0, it breaks scp and rcp and some other
applications. If it's always some arbitrary non-zero value, it breaks
pwd from coreutils and some other applications. If it's available and
doesn't match st_ino, it breaks another set of applications. If it's
not available at all, it breaks all applications asking for d_ino in any
way.
> Cygwin would then set it to 0 on WinNT and 2k (where it is
> prohibitively expensive to determine a real value), set it to the hash on
> Win9x and ME (since st_ino is also the hash on those platforms), and set
> it to the actual st_ino value on WinXP and beyond (since the API exists).
That would be a better solution, though it would still not be ok to set
it to 0 on NT4 and 2K. Maybe we should think about another way to
generate a hash value and use it on all platforms. I'm just at a loss
right now, to come up with another hash generation method, which would
allow to get the same inode number for hardlinks :-(
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
next prev parent reply other threads:[~2006-01-20 14:14 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-01-20 5:47 New platform independent problem djh
2006-01-20 11:08 ` Eli Zaretskii
2006-01-20 12:25 ` Corinna Vinschen
2006-01-20 13:59 ` Eric Blake
2006-01-20 14:14 ` Corinna Vinschen [this message]
2006-01-20 13:29 ` Igor Peshansky
2006-01-20 13:56 ` Eli Zaretskii
2006-01-20 14:18 ` Eric Blake
2006-01-20 16:48 ` Eli Zaretskii
2006-01-20 21:24 ` Andreas Schwab
2006-01-20 14:21 ` Corinna Vinschen
2006-01-27 20:45 ` Eli Zaretskii
2006-02-23 9:20 ` djh
-- strict thread matches above, loose matches on Subject: below --
2006-01-20 17:01 Eric Blake
2006-01-20 17:22 ` Eli Zaretskii
2006-01-28 14:18 ` Corinna Vinschen
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