On 2021-09-21 13:19, Florian Eckert wrote:
>
> I have written a small shell script, to track write access to the
> '/etc/config' directory.
> For this task I am using the inotify-tool package [1].
> I am using the inotifywait tool to add the watchers [2] with a small
> shell script and log them to the syslog.
>
> If I change a 'uci' option with the the 'uci' commands, then I get
> create and write events for a temporary file in the '/etc/config/'
> directory.
> I didn't expect it to be like this.
>
> For example, if I now change a file using the 'uci' command, a tmp file
> is created under '/etc/config'.
> Is this correct? Or do we have a problem there.
> I have always thought that for embedded systems with flashes it is
> important to make as few write accesses as possible.
>
> Shell commands to change uci config:
>
> root@st-dev-07 ~ # uci set system.led_Power.trigger=none
> root@st-dev-07 ~ # uci commit system
>
> Log output of my Script:
>
> Tue Sep 21 12:50:38 2021 daemon.info loginotify[17375]:
> {"directory":"/etc/config/","file":".system.uci-fEGgbp","event":"CREATE","time":"09/21/21
>
> 12:50:38"}
> Tue Sep 21 12:50:38 2021 daemon.info loginotify[17375]:
> {"directory":"/etc/config/","file":".system.uci-fEGgbp","event":"MODIFY","time":"09/21/21
>
> 12:50:38"}
> Tue Sep 21 12:50:38 2021 daemon.info loginotify[17375]:
> {"directory":"/etc/config/","file":".system.uci-fEGgbp","event":"MODIFY","time":"09/21/21
>
> 12:50:38"}
> Tue Sep 21 12:50:38 2021 daemon.info loginotify[17375]:
> {"directory":"/etc/config/","file":".system.uci-fEGgbp","event":"CLOSE_WRITE,CLOSE","time":"09/21/21
>
> 12:50:38"}
> Tue Sep 21 12:50:38 2021 daemon.info loginotify[17375]:
> {"directory":"/etc/config/","file":"system","event":"CLOSE_WRITE,CLOSE","time":"09/21/21
>
> 12:50:38"}
> Tue Sep 21 12:50:38 2021 daemon.info loginotify[17375]:
> {"directory":"/etc/config/","file":".system.uci-fEGgbp","event":"ATTRIB","time":"09/21/21
>
> 12:50:38"}
>
> I am bothered about the file '.system.uci-fEGgbp'?
The extra temporary file in /etc/config is intentional. uci is simply
using a common pattern in order to make rewriting config files atomic
and avoid leaving behind empty or incomplete files in case of a system
crash during commit.
The new file is written under a temporary name, and after a fsync, it is
renamed to the final filename. This only works if the temporary file and
the config file are on the same filesystem, that's why the temp file is
put in /etc/config as well.
- Felix
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