Is there some doc or some example of libbtrfs ?

Is there some doc or some example of libbtrfs ?

[Pierre Couderc]

Ho do I get programmatically the list of the snapshots of a volume in C/C++?

I can analyse the output of "btrfs li sh", but is there an easier way ?

I have found no doc or example...

Thanks

PC

Re: Is there some doc or some example of libbtrfs ?

[Nikolay Borisov]

On 7.08.20 г. 12:36 ч., Pierre Couderc wrote:
> Ho do I get programmatically the list of the snapshots of a volume in
> C/C++?
> 
> I can analyse the output of "btrfs li sh", but is there an easier way ?
> 
> I have found no doc or example...

Well, the example is in the source code of btrfs-progs, namely :

btrfs_list_subvols_print
 list_subvol_search

TLDR You'd have to use the TREE_SEARCH ioctl which allows you to get
data from btrfs' various trees. In order to figure out what data to pass
to  the ioctl you'd have to familiarize yourself with the internal
structure of btrfs trees to know which items represent a snapshot and
which proper subvolumes. You should check the "ROOT ITEM" description at
https://github.com/btrfs/btrfs-dev-docs/blob/master/tree-items.txt to
see when a root item is a snapshot and not a subvolume.

> 
> Thanks
> 
> PC
> 

Re: Is there some doc or some example of libbtrfs ?

[Pierre Couderc]

On 8/7/20 12:17 PM, Nikolay Borisov wrote:
>
> On 7.08.20 г. 12:36 ч., Pierre Couderc wrote:
>> Ho do I get programmatically the list of the snapshots of a volume in
>> C/C++?
>>
>>
>> Well, the example is in the source code of btrfs-progs, namely :
>>
>> btrfs_list_subvols_print
>>   list_subvol_search
>>
>> TLDR You'd have to use the TREE_SEARCH ioctl which allows you to get
>> data from btrfs' various trees. In order to figure out what data to pass
>> to  the ioctl you'd have to familiarize yourself with the internal
>> structure of btrfs trees to know which items represent a snapshot and
>> which proper subvolumes. You should check the "ROOT ITEM" description at
>> https://github.com/btrfs/btrfs-dev-docs/blob/master/tree-items.txt to
>> see when a root item is a snapshot and not a subvolume.
>>
Thank you, you are the light in the dark..

I start on that.

PC

Re: Is there some doc or some example of libbtrfs ?

[Pierre Couderc]

On 8/7/20 12:17 PM, Nikolay Borisov wrote:
>
> On 7.08.20 г. 12:36 ч., Pierre Couderc wrote:
>> Ho do I get programmatically btrfs xxxxx....?
>>
> Well, the example is in the source code of btrfs-progs, namely :
>
> btrfs_list_subvols_print
>   list_subvol_search
>
> TLDR You'd have to use the TREE_SEARCH ioctl which allows you to get
> data from btrfs' various trees. In order to figure out what data to pass
> to  the ioctl you'd have to familiarize yourself with the internal
> structure of btrfs trees to know which items represent a snapshot and
> which proper subvolumes. You should check the "ROOT ITEM" description at
> https://github.com/btrfs/btrfs-dev-docs/blob/master/tree-items.txt to
> see when a root item is a snapshot and not a subvolume.
>
A small tip for the next one :

To understand how and where some function is called (here 
btrfs_list_subvols_print), grep in in "cmds" subdirectory (here 
logically subvolume.c).

Re: Is there some doc or some example of libbtrfs ?

[David Sterba]

On Fri, Aug 07, 2020 at 11:36:10AM +0200, Pierre Couderc wrote:
> Ho do I get programmatically the list of the snapshots of a volume in C/C++?
> 
> I can analyse the output of "btrfs li sh", but is there an easier way ?
> 
> I have found no doc or example...

Please don't use libbtrfs, that's going to be removed in the future.
There's a proper library libbtrfsutil. See
btrfs_util_create_subvolume_iterator.

Re: Is there some doc or some example of libbtrfs ?

[Pierre Couderc]

On 8/10/20 5:13 PM, David Sterba wrote:
> On Fri, Aug 07, 2020 at 11:36:10AM +0200, Pierre Couderc wrote:
>> Ho do I get programmatically the list of the snapshots of a volume in C/C++?
>>
>> I can analyse the output of "btrfs li sh", but is there an easier way ?
>>
>> I have found no doc or example...
> Please don't use libbtrfs, that's going to be removed in the future.
> There's a proper library libbtrfsutil. See
> btrfs_util_create_subvolume_iterator.

ok I note that. Thnak you.