Re: chmod --cheap option

[Pádraig Brady]

On 25/05/16 07:31, Hrubák, András wrote:
> Hi Eric and Coreutils Members,
>
> I know about the risk of race condition. It would be just an option.
> If you tell about
> it in usage help, users will be notified about the risks and decide
> according to it.
> There are several usecases when this race condition is acceptable.
> Without this internal logic in chmod, scripters must write their own
> logic in upper level (eg. shell script: compute numeric mode from
> symbolic mode notation -> stat the file -> test the current mode
> against the old one -> call chmod conditionally, etc.), which means
> bigger probability of race condition.
> So I would state the risks of this option in help text, explaining the
> meaning of '--cheap', and of course make it NOT default.
> You can find the patch in attachment.

I think your use case here is to call fchmod()
but only update the ctime if needed?
That really can only be done without races within the kernel.
It would be dangerous to provide racy functionality otherwise,
as you could never implement anything robust with it,
or worse some might expect their implementation to be robust,
and encounter tricky race conditions later.

thanks,
Pádraig