Re: Pre-unblock: dash 0.5.5.1-7.3

[Jonathan Nieder <jrnieder@gmail.com>]

Adam D. Barratt wrote:

> diff -u dash-0.5.5.1/debian/dash.preinst dash-0.5.5.1/debian/dash.preinst
> --- dash-0.5.5.1/debian/dash.preinst
> +++ dash-0.5.5.1/debian/dash.preinst
> @@ -1,4 +1,4 @@
> -#!/bin/sh
> +#!/bin/bash
>  set -e
>  
>  divert() {
> @@ -6,16 +6,19 @@
>  	ltarget=$2
>  	div=$(dpkg-divert --list $dfile)
>  	distrib=${3:-$dfile.distrib}
> +	temp=$dfile.tmp
>  	if [ -z "$div" ]; then
> -		dpkg-divert --package dash --divert $distrib --add $dfile
>  		# This differs from dpkg-divert's --rename because we
>  		# first make a copy of $dfile (the file being diverted)
>  		# in $distrib. Then, a symlink to $ltarget is forcibly created
> -		# from $dfile.
> +		# from $dfile; this is performed in two stages with an
> +		# intermediate temporary file as ln -sf is not idempotent.

The word I was thinking of before is atomic.  ln -sf is not atomic.

>  		# dpkg-divert's --rename direct equivalent would be:
>  		# mv $dfile $distrib -- but we could end up without a symlink
>  		cp -dp $dfile $distrib
> -		ln -sf $ltarget $dfile
> +		ln -sf $ltarget $temp
> +		mv -f $temp $dfile
> +		dpkg-divert --package dash --divert $distrib --add $dfile

If preinst is interrupted after the mv but before the dpkg-divert,
then /bin/sh will point to dash but it will not be diverted yet, so if
bash were installed before preinst gets a chance to run again, /bin/sh
would be overwritten.  That seems fine to me, expected even.

Thanks, this looks good.

Jonathan