[LEDE-DEV] [PATCH] base-files: do not backup unchanged files

[Luiz Angelo Daros de Luca]

>> After applied, the list of files in backup in a fresh installation change from:
>> to:
>>
>> root at LEDE:~# sysupgrade  -l
>> /etc/config/dhcp
>> /etc/config/firewall
>> /etc/config/network
>> /etc/config/system
>> /etc/dropbear/dropbear_rsa_host_key
>>
>
> Hi,
>
> when I set up  new devices I usually do an export of the initial configuration to track
> the changes I made externally in a git repo.
> With this patch I would just get the five files mentioned above, thus an incomplete config and would not
> be able to track my config changes.

Hi,

Yes, a diff between two backups will not show actually what has changed as modified files will appear as new.

However, maybe a configuration backup is not the best way to keep track of changes on configuration files.
The list of "configuration file" can change as long as their configuration are not listed in /lib/upgrade/keep.d.
Backup consists of files listed in /etc/sysupgrade.conf, /lib/upgrade/keep.d and changed config files (tracked by opkg).
For example, /etc/firewall.user will not appear in backup if not modified (or opkg is missing) because it is not mentioned in
/lib/upgrade/keep.d. There are many more examples. Try yourself:

# find $(cat /lib/upgrade/keep.d/*) -type f -o type l 2>/dev/null | sort -u >/tmp/a.txt
# cat /usr/lib/opkg/info/*.conffiles | sort -u>/tmp/b.txt
# diff -u /tmp/a.txt /tmp/b.txt  | grep +

So, even today, it is already expected that a backup after fresh installation to have less files than a backup
after some packages where installed. I just made the difference bigger.

BTW, the backup is broken whenever opkg is missing, as those files will never get into backup. I don't know if it's worth it to try
to fix backup without opkg.

I could add a new option for sysupgrade in order to keep all files listed, even those untouched, in order to get the old behaviour.
However, in order to use it, you'll need to call it using a terminal. In this case, you could also retrieve those files using ssh+tar, or rsync if avaiable.
Anyway, this option would only make sense if I grab also all config files mentioned in any installed package, even those untouched.

I'm trying to make OpenWrt/LEDE upgrade process closer to what we get in a normal Linux distribution. The inclusion of only
modified files is a trick to reproduce the same logic rpm/deb uses for configuration updates (replace what wasn't touched,
keep what was modified). The current behaviour is already breaking installations by, at least, propagating outdated /etc/profile.
I'm trying to fix backup/upgrade process from now on, even if it could "break" the use of backup for things not related to restore/upgrade.
IMHO, it pays off.

I already have a patch v2 ready https://github.com/luizluca/source/tree/better-backups_skip-unchanged.
I'm just waiting because it is now based on the submitted "[PATCH] base-files: fix sysupgrade -b/-l when -c is used".
Or maybe I should just send already v2 including both.

Luiz