libvirt users - Oct 2020 - Re: Building libvirt library without libvirtd or virsh

On Thu, Oct 08, 2020 at 09:38:22AM +0200, Martin Kletzander
wrote:
> On Wed, Oct 07, 2020 at 04:50:26PM -0700, Román González wrote:
> > Hello there,
> > 
> > I'm trying to play with musl and libvirt to see if I'm able to
build a
> > libvirt client binary without dynamic lib dependencies. I have two
> > questions:
> > 
> > 1) to your knowledge, is this exercise futile?
> > 
> > 2) Do you know if there is a way to *only* compile the library bits?
> > 
> > I want to reduce the number of dependencies in the build, and only
> > construct the libvirt libraries, not libvirtd nor virsh.
> > 
> 
> You can disable building the daemon with -Ddriver_libvirtd=disabled (if I
am
> reading the code correctly).  I do not think there is something similar for
the
> clients, but I might be wrong.  Pavel (Cc'd) would definitely know or
at least
> be able to find it out more easily.  If it is not possible now then it
should
> not be that difficult to add such option, I think.
Correct, using that option you can disable libvirtd which should reduce
some dependencies but there is no option to disable virsh. We can
possibly introduce an option to disable libvirt clients but that would
save you only readline as a dependency which you can disable by using
-Dreadline=disabled .

If you want to do a minimal build of libvirt you can run meson with
--auto-features=disabled which will disable most of the features and you
can explicitly enable only the things that you want to use (this is what
most distributions are doing when building packages). I just noticed
that there are some build options where this doesn't work so I'll post
patches to fix them.

The last part I have to ask what do you mean by "without dynamic lib
dependencies"? If you mean that libvirt.so should be statically linked
that is not currently possible. We would have to add option to make it
possible and update all dependency() and find_library() calls in all
meson.build files to look only for static libraries.

In addition I think we should add build options which would allow users
to disable tests, documentation, examples and other bits that end-users
don't have to use.

Pavel

>
> If you want to do a minimal build of libvirt you can run meson with
> --auto-features=disabled which will disable most of the features and you
> can explicitly enable only the things that you want to use (this is what
> most distributions are doing when building packages). I just noticed
> that there are some build options where this doesn't work so I'll
post
> patches to fix them.

When you happen to do this, can you share a link where I can download the
patches?

The last part I have to ask what do you mean by "without dynamic
lib
> dependencies"? If you mean that libvirt.so should be statically linked
> that is not currently possible. We would have to add option to make it
> possible and update all dependency() and find_library() calls in all
> meson.build files to look only for static libraries.
>
Uh, I wonder what the meson option

default_library         shared
>                        [shared, static, both]
>
is for?

In addition I think we should add build options which would allow
users
> to disable tests, documentation, examples and other bits that end-users
> don't have to use.
>
That makes sense.

Thank you Martin and Pavel for replying back so quickly. I'll try to do the
compilation with the auto features disabled and  see how long I can  go
from there, this is probably going to be a whack-a-mole game

On Thu, Oct 8, 2020 at 3:18 AM Pavel Hrdina <phrdina@redhat.com> wrote:
> On Thu, Oct 08, 2020 at 09:38:22AM +0200, Martin Kletzander wrote:
> > On Wed, Oct 07, 2020 at 04:50:26PM -0700, Román González wrote:
> > > Hello there,
> > >
> > > I'm trying to play with musl and libvirt to see if I'm
able to build a
> > > libvirt client binary without dynamic lib dependencies. I have
two
> > > questions:
> > >
> > > 1) to your knowledge, is this exercise futile?
> > >
> > > 2) Do you know if there is a way to *only* compile the library
bits?
> > >
> > > I want to reduce the number of dependencies in the build, and
only
> > > construct the libvirt libraries, not libvirtd nor virsh.
> > >
> >
> > You can disable building the daemon with -Ddriver_libvirtd=disabled
(if
> I am
> > reading the code correctly).  I do not think there is something
similar
> for the
> > clients, but I might be wrong.  Pavel (Cc'd) would definitely know
or at
> least
> > be able to find it out more easily.  If it is not possible now then it
> should
> > not be that difficult to add such option, I think.
>
> Correct, using that option you can disable libvirtd which should reduce
> some dependencies but there is no option to disable virsh. We can
> possibly introduce an option to disable libvirt clients but that would
> save you only readline as a dependency which you can disable by using
> -Dreadline=disabled .
>
> If you want to do a minimal build of libvirt you can run meson with
> --auto-features=disabled which will disable most of the features and you
> can explicitly enable only the things that you want to use (this is what
> most distributions are doing when building packages). I just noticed
> that there are some build options where this doesn't work so I'll
post
> patches to fix them.
>
> The last part I have to ask what do you mean by "without dynamic lib
> dependencies"? If you mean that libvirt.so should be statically linked
> that is not currently possible. We would have to add option to make it
> possible and update all dependency() and find_library() calls in all
> meson.build files to look only for static libraries.
>
> In addition I think we should add build options which would allow users
> to disable tests, documentation, examples and other bits that end-users
> don't have to use.
>
> Pavel
>

On Thu, Oct 08, 2020 at 11:18:08AM -0700, Román González
wrote:
> >
> > If you want to do a minimal build of libvirt you can run meson with
> > --auto-features=disabled which will disable most of the features and
you
> > can explicitly enable only the things that you want to use (this is
what
> > most distributions are doing when building packages). I just noticed
> > that there are some build options where this doesn't work so
I'll post
> > patches to fix them.
> 
> 
> When you happen to do this, can you share a link where I can download the
> patches?
They are now pushed to master branch.
> The last part I have to ask what do you mean by "without dynamic lib
> > dependencies"? If you mean that libvirt.so should be statically
linked
> > that is not currently possible. We would have to add option to make it
> > possible and update all dependency() and find_library() calls in all
> > meson.build files to look only for static libraries.
> >
> 
> Uh, I wonder what the meson option
> 
> default_library         shared
> >                        [shared, static, both]
> >
> 
> is for?
You can read more about it here [1] but basically it applies to
libraries build within the project. In libvirt all internal libraries
are build as static.
> In addition I think we should add build options which would allow users
> > to disable tests, documentation, examples and other bits that
end-users
> > don't have to use.
> >
> 
> That makes sense.
I did not introduce option to disable examples because that is probably
pointless but there are already pushed new options for documentation and
tests.
> > If you want to do a minimal build of libvirt you can run meson with
> > --auto-features=disabled which will disable most of the features and
you
> > can explicitly enable only the things that you want to use (this is
what
> > most distributions are doing when building packages). I just noticed
I need to correct myself as this statement was not true. RPM packages
use --auto-features=enabled by default.

Pavel

[1] <https://mesonbuild.com/Reference-manual.html#library>