[augeas-devel] Saving changed tree to file does not work but no error message

Fri Jan 15 21:03:29 UTC 2016

Dear Raphaël,

thanks for your reply and your patience.
Unfortunately I couldn’t solve my problem yet; thus, I will provide here further information.

If I use augtool, I can change the value of the node and also save the changes to the config file. So, this works fine.
I created a shell script (in the folder src) which executes all the individual commands.
Here the output of the shell script:
=========================================START
pi at raspberrypi ~/AugeasDemoC $ sudo sh ./src/equivalentAugtoolCommands.sh 
/augeas/load
/augeas/load/Interfaces
/augeas/load/Interfaces/lens = "Interfaces.lns"
/augeas/load/Interfaces/incl = "/home/pi/AugeasDemoC/network/interfaces"
Saved 1 file(s)
/augeas/events/saved = "/files/home/pi/AugeasDemoC/network/interfaces“
=========================================END

In contrast, the C++ program does not save the changed node value back to the file. However, the program does not give any error message.
Here the output of the program:

=========================================START
pi at raspberrypi ~/AugeasDemoC $ ./augeasDemo 
Execution path is: /home/pi/AugeasDemoC/network/interfaces/

Here we start the initialization.
Set lens: 0
Set incl: 0
Load augeas: 0
Number of errors: 0

Here we start searching for a specific node.
Number of matches: 3
The following paths have been found:
/files/home/pi/AugeasDemoC/network/interfaces/iface[1]
/files/home/pi/AugeasDemoC/network/interfaces/iface[2]
/files/home/pi/AugeasDemoC/network/interfaces/iface[3]
Interface number of wlan0: 3

Here we start changing the value of the node.
Set value: 0
Augeas version: 1.4.0
The value read from node: dhcp	<<<<——— That means the value has been changed.

Here we start saving changes back to files.
Save mode set: 0
File saved: 0
Number of stored files: 0
Number of errors: 0
Return: 0
=========================================END

All the code can be found here: https://github.com/cmolitor/AugeasDemoC/tree/simple

I really have no idea what I am doing wrong and I am really grateful for suggestions and help.
Excuse also my not so nice programming style as I am not a professional programmer. Suggestions are welcome as well. I will have a look at the xpath in the next steps.

Cheers,
Christoph

Am 11.01.2016 um 09:38 schrieb Raphaël Pinson <raphael.pinson at camptocamp.com>:

> Hello Christoph,
> 
> 
> 
> On Sun, Jan 10, 2016 at 6:09 PM, Christoph Molitor <christoph.molitor at googlemail.com> wrote:
> Hello Raphaël,
> 
> thanks for your reply and your suggestions.
> I added some code to read the error messages. 
> When I execute the code there are no error messages but still the changes made to the value of one node are not saved back to the configuration file.
> The latest source code can be found here:
> https://github.com/cmolitor/AugeasDemoC/blob/simple/src/main.cpp
> 
> 
> You need to really look into how to use XPath in Augeas. You can remove pretty much all of https://github.com/cmolitor/AugeasDemoC/blob/simple/src/main.cpp#L93-L111 (and probably more) by using proper XPath expressions instead of manually parsing the tree node by node.
> 
> 
> Also, Augeas 1.0.0 introduced aug_transform, which is easier/better than manually manipulating nodes in /augeas/load.
> 
>  
> 
> I also went through all the steps using augtool and added the commands as comments to the source code.
> If I execute the commands in augtool the changes are saved to the configuration file.
> 
> In general, I can load the configuration file, change the value, check that the value has been really changed by reading it again. Calling aug_save() does not give an error message but still the changes are not saved to the file.
> 
> 
> And what is the output of your code then?
> 
>  
> I tried this with augeas version 1.2 and 1.4.
> 
> It would be great if I could get further advice how to proceed or a hint what I am doing wrong.
> 
> I will also have a look at netcf but could not find a detailed documentation yet.
> 
> 
> netcf has been used for a few years in libvirt. See https://github.com/saaros/libvirt/blob/master/src/interface/interface_backend_netcf.c for example.
> 
> 
> 
> Cheers,
> 
> Raphaël
> 
> 
>  
> Am 04.01.2016 um 09:44 schrieb Raphaël Pinson <raphael.pinson at camptocamp.com>:
> 
>> Hello Christoph and happy new year to you too!
>> 
>> 
>> Your code doesn't check for errors (either parsing or saving errors). You could add checks (looking for `/augeas//error` nodes) just after your call to aug_load (for parsing errors) and to aug_save (for saving errors).
>> 
>> One way to debug your code would also be to try it with augtool, which would be easier to debug.
>> 
>> Also, are you aware of the netcf project, which provides a higher API on top of Augeas to access and modify /etc/network/interfaces?
>> 
>> 
>> 
>> Cheers,
>> 
>> Raphaël
>> 
>> 
>> 
>> 
>> 
>> On Fri, Jan 1, 2016 at 5:05 PM, Christoph Molitor <christoph.molitor at googlemail.com> wrote:
>> Dear all,
>> 
>> first of all a happy new year to everyone.
>> 
>> I am trying to use the augeas C API to apply changes to the "/etc/network/interfaces" file.
>> So far I was able to apply changes to the tree. However, I am not able to save the changes back to the file.
>> First, I thought it is a problem with the permissions. However, I copied the interfaces file to a different folder and it still does not work.
>> Using the command line tool augtool, I am able to make the changes and save them to the file.
>> 
>> I uploaded an (almost) minimal version of my program to:
>> https://github.com/cmolitor/AugeasDemoC
>> 
>> The repository includes an example „interfaces“.
>> I am working on a Raspberry Pi with Raspbian Jessie.
>> It would be great if someone could give me a hint what I am doing work and where the problem might come from.
>> 
>> Thanks for your support!
>> 
>> Christoph
>> 
>> _______________________________________________
>> augeas-devel mailing list
>> augeas-devel at redhat.com
>> https://www.redhat.com/mailman/listinfo/augeas-devel
>> 
>> 
>> 
>> -- 
>> Raphaël Pinson
>> Infrastructure Developer & Training Leader
>> +33 458 482 013
>> 
>> Camptocamp France
>> Savoie Technolac
>> BP 352
>> 48, avenue du Lac du Bourget
>> 73372 Le Bourget du Lac, Cedex
>> www.camptocamp.com
> 
> 
> 
> 
> -- 
> Raphaël Pinson
> Infrastructure Developer & Training Leader
> +33 458 482 013
> 
> Camptocamp France
> Savoie Technolac
> BP 352
> 48, avenue du Lac du Bourget
> 73372 Le Bourget du Lac, Cedex
> www.camptocamp.com

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