[Duplicity-talk] Re: Preventing access time modification?

[Axel Beckert]

Hi Sam,

On Tue, Jun 12, 2007 at 04:32:44PM +0100, Sam Morris wrote:
> [Sent with private mail because my posts to the ML aren't getting
> through for some reason]

So I (nearly) fullquote back to the list. :-)

[How to avoid modifiying the access time]
> The 'open' system call can accept the O_NOATIME flag.

I already heard about embedded systems which don't use access time at
all, but I didn't know that you just need a flag to open(2).

> From glibc's docs:
>          -- Macro: int O_NOATIME
>              If this bit is set, `read' will not update the access
>              time of the file. *Note File Times::. This is used by
>              programs that do backups, so that backing a file up
>              does not count as reading it. Only the owner of the
>              file or the superuser may use this bit.

Isn't that exactly what duplicity needs? :-)

> and from manpages:
> 
>         O_NOATIME
>                (Since Linux 2.6.8)

Ok, that explains why I haven't heard about it yet. The feature is not
that old. Funny, somehow.

>                Do not update the file last access time (st_atime in
>                the inode) when the file is read(2). This flag is
>                intended for use by indexing or backup programs,
>                where its use can significantly reduce the amount of
>                disk activity. This flag may not be effective on all
>                filesystems. One example is NFS, where the server
>                maintains the access time.
>         
> so whether you must be the file owner (or root) to use it may be
> dependant on the operating system in question.

And I wonder if it works on elder glibc respectively since when glibc
supports this feature.

> IMO duplicity should have an option that turns this on by default
> for the whole backup.

Full Ack! That's much easier than my conception of setting it back. An
much more performant. Even more performant than the current way. :-)

Thanks for your advice!

                Regards, Axel
-- 
Axel Beckert - address@hidden, address@hidden - http://noone.org/abe/