Re: zstd compressed kernels

[Jan Beulich <jbeulich@xxxxxxxx>]

On 20.01.2021 00:10, Michael Young wrote:
> I have been trying the "[PATCH v2 1/5] libxenguest: support zstd 
> compressed kernel" patch, and (assuming I haven't broken anything trying 
> to migrate it to 4.14) it fails with
> 
> onfigure: error: Package requirements (libzstd) were not met:
> 
> Package 'libzstd', required by 'virtual:world', not found
> 
> Consider adjusting the PKG_CONFIG_PATH environment variable if you
> installed software in a non-standard prefix.
> 
> Alternatively, you may set the environment variables libzstd_CFLAGS
> and libzstd_LIBS to avoid the need to call pkg-config.
> See the pkg-config man page for more details.
> configure: error: ./configure failed for tools
> 
> I didn't give it any zstd packages so I would expect this test to fail, 

Hmm, maybe I either misunderstood the purpose of
PKG_CHECK_MODULES(), or didn't use it correctly. The goal clearly
is for there to be no failure, but simply a libxenguest without
zstd decompression support. But I will admit I didn't try
configuring on a system without libzstd; apparently I should have.

I specifically didn't want to use AC_CHECK_HEADER() / AC_CHECK_LIB()
since pkg-config is - aiui - to help abstract the need to know where
exactly to look for headers and libraries of a particular package,
and libzstd comes with a libzstd.pc "out of the box". Cc-ing the
tools maintainers in the hope they may know right away what my
mistake here is.

> but I would have expected the build to continue and attempt to use the 
> zstd code in the xen tree instead.

No, this - very specifically - is not the intention. This also isn't
how things work for the other compression methods. The hypervisor
code gets reused only for the stubdom build.

Jan