Libguestfs - Apr 2020 - Re: [PATCH nbdkit 1/2] server: Add pkg-config file to compile against locally compiled nbdkit.

Version 1 was here:
https://www.redhat.com/archives/libguestfs/2020-April/thread.html#00160

Version 2 side-steps the objections to the first patch by using a
well-formed alternate nbdkit.pc file and running ordinary pkg-config
against it, so any parsing of --cflags etc will be done by pkg-config.

The first patch is essentially the same idea as:

https://github.com/libguestfs/libnbd/commit/dc87a1a6d6918ac5477e1d6b225998ff7fedc86e

(which follows on from similar tricks in libguestfs and libvirt).

Rich.

In most cases it is incorrect to use this - pay attention to the note
at the top of the newly added file.
---
 .gitignore                |  1 +
 configure.ac              |  1 +
 server/local/nbdkit.pc.in | 45 +++++++++++++++++++++++++++++++++++++++
 3 files changed, 47 insertions(+)

diff --git a/.gitignore b/.gitignore
index 4f6fcf1b..8c701295 100644
--- a/.gitignore
+++ b/.gitignore
@@ -83,6 +83,7 @@ plugins/*/*.3
 /plugins/tar/nbdkit-tar-plugin
 /plugins/tmpdisk/default-command.c
 /podwrapper.pl
+/server/local/nbdkit.pc
 /server/nbdkit
 /server/nbdkit.pc
 /server/synopsis.c
diff --git a/configure.ac b/configure.ac
index b71d9d8c..17d8d676 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1088,6 +1088,7 @@ AC_CONFIG_FILES([Makefile
                  filters/truncate/Makefile
                  filters/xz/Makefile
                  fuzzing/Makefile
+                 server/local/nbdkit.pc
                  server/Makefile
                  server/nbdkit.pc
                  tests/functions.sh
diff --git a/server/local/nbdkit.pc.in b/server/local/nbdkit.pc.in
new file mode 100644
index 00000000..96c33d2f
--- /dev/null
+++ b/server/local/nbdkit.pc.in
@@ -0,0 +1,45 @@
+# nbdkit
+# Copyright (C) 2013-2020 Red Hat Inc.
+#
+# Redistribution and use in source and binary forms, with or without
+# modification, are permitted provided that the following conditions are
+# met:
+#
+# * Redistributions of source code must retain the above copyright
+# notice, this list of conditions and the following disclaimer.
+#
+# * Redistributions in binary form must reproduce the above copyright
+# notice, this list of conditions and the following disclaimer in the
+# documentation and/or other materials provided with the distribution.
+#
+# * Neither the name of Red Hat nor the names of its contributors may be
+# used to endorse or promote products derived from this software without
+# specific prior written permission.
+#
+# THIS SOFTWARE IS PROVIDED BY RED HAT AND CONTRIBUTORS ''AS
IS'' AND
+# ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
+# THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A
+# PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL RED HAT OR
+# CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+# SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+# LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
+# USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
+# ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
+# OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
+# OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+# SUCH DAMAGE.
+
+# This alternate pkg-config file may be used to compile plugins
+# against a locally compiled (but not installed) nbdkit.  Note you
+# probably should *not* use this in most cases, since your plugin will
+# may end up containing hard paths to the local nbdkit sources.
+
+prefix=@abs_top_builddir@
+exec_prefix=@abs_top_builddir@
+
+Name: @PACKAGE_NAME@
+Version: @PACKAGE_VERSION@
+Description: A toolkit for creating NBD servers
+Requires:
+Cflags: -I@abs_top_srcdir@/include -I@abs_top_builddir@/include
+Libs:
-- 
2.18.2

When compiling when an older nbdkit is installed, the build would fail
because certain symbols such as .get_ready were not defined:

  ../../src/libguestfs.org/nbdkit/nbdkit.go:541:8: plugin.get_ready undefined
(type _Ctype_struct_nbdkit_plugin has no field or method get_ready)

This happens because we were using the installed <nbdkit-plugin.h>
rather than the local copy.

We don't want to modify the *.go files themselves as they might be
copied into other projects.  Instead we can set PKG_CONFIG_PATH to
point to the local nbdkit.pc which will return the correct CFLAGS.

Fixes: commit 1ff44288ae1cf95428283e252edd9474c3fe3b55
Thanks: Dan Berrangé, Eric Blake
---
 plugins/golang/Makefile.am | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/plugins/golang/Makefile.am b/plugins/golang/Makefile.am
index f189184c..d8d19b7a 100644
--- a/plugins/golang/Makefile.am
+++ b/plugins/golang/Makefile.am
@@ -66,18 +66,21 @@ noinst_DATA = \
 examples/dump-plugin/nbdkit-godump-plugin.so: \
 	    $(plugin_sources) examples/dump-plugin/dumpplugin.go
 	cd examples/dump-plugin && \
+	PKG_CONFIG_PATH="$(abs_builddir)/server/local" \
 	GOPATH="$(abs_builddir)" \
 	$(GOLANG) build -o nbdkit-godump-plugin.so -buildmode=c-shared
 
 examples/minimal/nbdkit-gominimal-plugin.so: \
 	    $(plugin_sources) examples/minimal/minimal.go
 	cd examples/minimal && \
+	PKG_CONFIG_PATH="$(abs_builddir)/server/local" \
 	GOPATH="$(abs_builddir)" \
 	$(GOLANG) build -o nbdkit-gominimal-plugin.so -buildmode=c-shared
 
 examples/ramdisk/nbdkit-goramdisk-plugin.so: \
 	    $(plugin_sources) examples/ramdisk/ramdisk.go
 	cd examples/ramdisk && \
+	PKG_CONFIG_PATH="$(abs_builddir)/server/local" \
 	GOPATH="$(abs_builddir)" \
 	$(GOLANG) build -o nbdkit-goramdisk-plugin.so -buildmode=c-shared
 
@@ -87,6 +90,7 @@ check_DATA = test/nbdkit-gotest-plugin.so
 
 test/nbdkit-gotest-plugin.so: $(plugin_sources) test/test.go
 	cd test && \
+	PKG_CONFIG_PATH="$(abs_builddir)/server/local" \
 	GOPATH="$(abs_builddir)" \
 	$(GOLANG) build -o nbdkit-gotest-plugin.so -buildmode=c-shared
 
-- 
2.18.2

On Thu, Apr 23, 2020 at 07:04:13PM +0100, Richard W.M. Jones
wrote:
> Version 1 was here:
> https://www.redhat.com/archives/libguestfs/2020-April/thread.html#00160
> 
> Version 2 side-steps the objections to the first patch by using a
> well-formed alternate nbdkit.pc file and running ordinary pkg-config
> against it, so any parsing of --cflags etc will be done by pkg-config.
> 
> The first patch is essentially the same idea as:
> 
>
https://github.com/libguestfs/libnbd/commit/dc87a1a6d6918ac5477e1d6b225998ff7fedc86e
> 
> (which follows on from similar tricks in libguestfs and libvirt).
For both patches

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>

Regards,
Daniel
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On Thu, Apr 23, 2020 at 07:04:14PM +0100, Richard W.M. Jones
wrote:
> +# probably should *not* use this in most cases, since your plugin will
> +# may end up containing hard paths to the local nbdkit sources.
"will may" -> "may" in my local copy.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
Read my programming and virtualization blog: http://rwmj.wordpress.com
virt-p2v converts physical machines to virtual machines.  Boot with a
live CD or over the network (PXE) and turn machines into KVM guests.
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On 4/23/20 1:04 PM, Richard W.M. Jones wrote:
> When compiling when an older nbdkit is installed, the build would fail
> because certain symbols such as .get_ready were not defined:
> 
>    ../../src/libguestfs.org/nbdkit/nbdkit.go:541:8: plugin.get_ready
undefined (type _Ctype_struct_nbdkit_plugin has no field or method get_ready)
> 
> This happens because we were using the installed <nbdkit-plugin.h>
> rather than the local copy.
> 
> We don't want to modify the *.go files themselves as they might be
> copied into other projects.  Instead we can set PKG_CONFIG_PATH to
> point to the local nbdkit.pc which will return the correct CFLAGS.
> 
> Fixes: commit 1ff44288ae1cf95428283e252edd9474c3fe3b55
> Thanks: Dan Berrangé, Eric Blake
> ---
>   plugins/golang/Makefile.am | 4 ++++
>   1 file changed, 4 insertions(+)
> 
> diff --git a/plugins/golang/Makefile.am b/plugins/golang/Makefile.am
> index f189184c..d8d19b7a 100644
> --- a/plugins/golang/Makefile.am
> +++ b/plugins/golang/Makefile.am
> @@ -66,18 +66,21 @@ noinst_DATA = \
>   examples/dump-plugin/nbdkit-godump-plugin.so: \
>   	    $(plugin_sources) examples/dump-plugin/dumpplugin.go
>   	cd examples/dump-plugin && \
> +	PKG_CONFIG_PATH="$(abs_builddir)/server/local" \
Shouldn't this be more like:

PKG_CONFIG_PATH="$(abs_builddir)/server/local$${PKG_CONFIG_PATH:-:$$PKG_CONFIG_PATH}"

so as to preserve any inherited override locations for other .pc files 
that might also be needed by cgo?

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org