[linux-lvm] Can't get merge in background using blockdev api to work

[Vojtech Trefny]

Hi, libblockdev maintainer here, libblockdev is a separate project from LVM
so it's better to ask on our GitHub[1], but I'm reading this ML too so I
can answer here.

I did a quick test and the background merge works for me, so I think the
problem is somewhere in LVM or with your setup, not in libblockdev -- all
we do is run the "lvm lvconvert --merge <vg>/<snap> --background" command
so there isn't a big room for a bug in our code (but I'm not saying there
isn't one). I've modified your code a little bit[2], can you try running it
again? I've just added logging so we can see what we actually tell LVM to
run and also enabled LVM logging and saved the log to /tmp/lvm.log.

[1] https://github.com/storaged-project/libblockdev
[2] https://gist.github.com/vojtechtrefny/7f379596958a0c4cd4c287c3f7a7dddd

On Mon, Jan 3, 2022 at 9:06 AM Tomas Dalebjörk <tomas.dalebjork at gmail.com>
wrote:

> Hi,
>
> I am trying to start a merge to the previous snapshot to be started with
> the "-b" flag (background). But it seems to be that the merging has not
> started in the background at all.
>
>         BDExtraArg      lv_arg = {"--background",""};
>         const BDExtraArg        *extra_args[2] = {&lv_arg, NULL};
>
>         BDPluginSpec lvm_plugin = {BD_PLUGIN_LVM, "libbd_lvm.so.2"};
>         BDPluginSpec *plugins[] = {&lvm_plugin,NULL};
>
>         bd_switch_init_checks (FALSE, &error);
>         bd_ensure_init (plugins, NULL, &error);
>         bd_lvm_lvsnapshotmerge(vg_name,lv_snap,extra_args,&error);
>
> Couldn't find any details about how to do this using the libblockdev api,
> but according to the documentation, it should be possible to add the same
> flags as for the normal LVM commands.
>
> Could you please give me a hint of what I am doing wrong?
>
> Regards Tomas
>
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