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Re: touch

From: ctrn3e8
Subject: Re: touch
Date: Tue, 29 Dec 2009 11:58:56 -0700
User-agent: Mozilla/5.0 (X11; U; Linux x86_64; en-US; rv: Gecko/20091215 Shredder/3.0

On 12/28/2009 07:10 AM, Eric Blake wrote:
Hash: SHA1

According to ctrn3e8 on 12/20/2009 10:04 PM:
    touch -m no longer seems to modify the file modification date.  Archlinux,
    coreutils-8.2 (package coreutils-8.2-1-i686).  Works if use coreutils-7.6.

What kernel version on which architecture (uname -a)?  Can you send an
strace?  We recently fixed a bug with kernel 2.6.32 failing to change
ctime when you use 'touch -a'; I wonder if there is another kernel bug we
need to be aware of.

execve("/bin/touch", ["touch", "-m", "startTimidity"], [/* 56 vars */]) = 0
utimensat(0, NULL, {UTIME_OMIT, UTIME_NOW}, 0) = 0
It now appears from lkml traffic that this issue has been fixed for most
file systems in concert with kernel 2.6.32 or newer, if you are running a
bleeding-edge ntfs-3g file system.  However, gnulib should keep a
workaround for the next couple years or so, until we can be reasonably
sure that it is easier to tell people to update their file systems than to
keep the workaround that (slightly) penalizes working file systems (the
lkml list pointed out that our most common use of the utimensat syscall is
via the futimens interface, where the kernel already has the file metadata
in cache because of the open() and/or fstat()).

But I still need a couple more pieces of information, before I know
whether the workaround requires a gettime() or whether it is cheaper and
only requires fstat().  We have proven the bug you reported against
ntfs-3g occurs with UTIME_OMIT/UTIME_NOW.  Does your unpatched ntfs-3g
file system also exhibit the bug with UTIME_OMIT/valid (test this by using
'touch --ref file1 -m file2', and report whether file2 changed mtime and
ctime).  Also, does the bug occur with valid/UTIME_NOW (this is harder to
test; touch does not expose that interface.  I'm not even sure that the
gnulib test exercised this; but you could at least report the results of
'make -k check' from your coreutils source directory, if you have built
from source.  If you need help writing a simple C program that tests this,
let me know).

- --
Don't work too hard, make some time for fun as well!

Eric Blake             address@hidden
Version: GnuPG v1.4.9 (Cygwin)
Comment: Public key at home.comcast.net/~ericblake/eblake.gpg
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org/


Re: touch --ref file1 -m file2   or touch -m file1 --ref file2
Does not work on ntfs-3g.  See attached

valid/UTIME_NOW , make -k stuff
I did not build coreutils from source.  I have been using the Archlinux 
packages which are pre-built binaries.  I can build and make install from 
source, but if I do that I probably prefer to set up a 'sandbox', just to be 
safe..I know I can use make --uninstall to revert....but really don't want to 
get crazy if something goes wrong trying to removing all the little pieces left 
splattered around. It's probably a couple of hours to set up a sandbox, so if 
you really need it, just let me know and I will see what I can come up with.   
Also would need how to get 'valid' ..I asumme coding something like 
utimensat(0, NULL, { {1262110412, 0},UTIME_OMIT}, 0) = 0  would work.

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