Re: [PATCH] modules: CONFIG_MODULE_COMPRESS: add hint that userspace support may easily be missing.

Andreas Mohr
2015-06-04T19:53:38Z

On Wed, Jun 03, 2015 at 11:31:20PM -0300, Lucas De Marchi wrote:
> On Wed, Jun 3, 2015 at 10:30 PM, Rusty Russell <rusty@rustcorp.com.au> wrote:
> > diff --git a/init/Kconfig b/init/Kconfig
> > index 968a001790af..5422c44be5f0 100644
> > --- a/init/Kconfig
> > +++ b/init/Kconfig
> > @@ -1948,26 +1948,22 @@ config MODULE_COMPRESS
> > bool "Compress modules on installation"
> > depends on MODULES
> > help
> > - This option compresses the kernel modules when 'make
> > - modules_install' is run.
> >
> > - The modules will be compressed either using gzip or xz depend on the
> > - choice made in "Compression algorithm".
> > + Compresses kernel modules when 'make modules_install' is run; gzip or
> > + xz depending on "Compression algorithm" below.
> >
> > - module-init-tools has support for gzip format while kmod handle gzip
> > - and xz compressed modules.
> > + module-init-tools supports gzip, and kmod can be configured to handle
> > + gzip and xz (but doesn't by default, at least as of version 18!).
>
> This is pretty much misleading. There's no such a default option. It's
> like saying kernel doesn't support feature X, Y or Z by default
> because make defconfig doesn't turn them on.
>
> The option is there since the beginning for the distros to adapt to their needs.

Hmm? Perhaps I'm misunderstanding something in this discussion,
but Debian kmod-20 (kmod_20.orig.tar.xz - BTW side note:
noted the .xz file rather than .gz? ;))
configure.ac contains:

AC_ARG_WITH([xz],
AS_HELP_STRING([--with-xz], [handle Xz-compressed modules
@<:@default=disabled@:>@]),
[], [with_xz=no])
AS_IF([test "x$with_xz" != "xno"], [
PKG_CHECK_MODULES([liblzma], [liblzma >= 4.99])
AC_DEFINE([ENABLE_XZ], [1], [Enable Xz for modules.])
], [
AC_MSG_NOTICE([Xz support not requested])
])

AC_ARG_WITH([zlib],
AS_HELP_STRING([--with-zlib], [handle gzipped modules
@<:@default=disabled@:>@]),
[], [with_zlib=no])

So it clearly seems there *is* a specific
(hard-coded, as opposed to system introspection) default
(i.e., the usual way of getting defaults, namely to simply not specify
--with-something configure options),
and that is (drumroll...) "disabled".

Andreas