Date: Thu, 26 Mar 1998 10:48:46 +1100 From: Bruce Evans <bde@zeta.org.au> To: freebsd-bugs@hub.freebsd.org, syssgm@dtir.qld.gov.au Subject: Re: bin/6124: Getting md5 to reset access times. Message-ID: <199803252348.KAA30982@godzilla.zeta.org.au>
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> > If you are using md5 to checksum a load of files you probably
> > don't want all the access times changed. This is a small patch
> > which adds a "-r" flag which resets the access times to what
> > they were before the file was checksumed.
>
> The updated manual page should point out that resetting the access time
> updates the inode change time.
This is fundamental - all POSIX syscalls that change the inode update
the inode change time. This is well documented in the POSIX.1 and should
be documented in the section 2 man pages. utime.2 doesn't even mention
the inode change time. Sigh.
> For me the inode change time is much
> more interesting than the access time since dump checks ctime as well as
> mtime to determine if a file has changed, and since hackers leave more
> interesting footprints in ctime stamps than atime stamps.
I think it's more important for almost everything. The ctime should
be used by backup programs. It is the only indication that the inode
has changed. Gnu tar has a --atime-preserve option, but it is almost
useless since using it clobbers the inode change times. I think the
mtree option would be even more useless, since it is more important to
have exlusive access to the file systems for security-related things
than for tar backups and when you have exclusive access you can mount
the file systems -noatime.
> Regardless, the utime and utimes manual pages need some updating, which
> I'm happy to do once the proper behaviour is defined.
>
> >+ if( times_ok ) {
> >+ TIMESPEC_TO_TIMEVAL(&tv[0], &sb.st_atimespec);
> >+ TIMESPEC_TO_TIMEVAL(&tv[1], &sb.st_mtimespec);
> >+
> >+ utimes(argv[optind],tv);
> >+ }
>
> This interesting use of TIMESPEC_TO_TIMEVAL may be of value in the future,
> but ffs_update() only uses the tv_sec portion, and throws the rest away.
Some file systems actually use the tv_usec or tv_nsec portion. utime.2
says that utime(2) is obsoleted by utimes(2). The reverse is closer to
being true (the POSIX utime() is better than the old one). utimes()
is useless since it can't preserve tv_nsec and the most important file
system throws away even the tv_usec portion. Programs that attempt to
preserve timestamps might as well use utime() to be standard and honestly
broken.
Bruce
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