Libguestfs - Mar 2020 - Re: [PATCH libguestfs 1/2] build: Allow C programs using libguestfs to be compiled against build dir.

These changes allow virt-v2v to be compiled against the build
directory of a non-installed libguestfs.

Note that some small changes are also required to common and virt-v2v
itself.  I will post those separately.

Rich.

We use a similar trick to libvirt to allow external C programs that
use libguestfs to be compiled against the built (but not installed)
libguestfs with:

  ../libguestfs/run ./configure
  make

What actually happens is we have a second pkg-config file
(lib/local/libguestfs.pc) which points to the locally built
libguestfs.  The ./run script sets up PKG_CONFIG_PATH to point to this
directory.  Assuming that ./configure is using pkg-config/pkgconf and
not some other half-baked solution it will pick up the libguestfs.pc
file from here which will set CFLAGS and LIBS appropriately.
---
 .gitignore                 |  1 +
 configure.ac               |  1 +
 lib/Makefile.am            |  1 +
 lib/local/libguestfs.pc.in | 36 ++++++++++++++++++++++++++++++++++++
 run.in                     |  5 +++++
 5 files changed, 44 insertions(+)

diff --git a/.gitignore b/.gitignore
index 1abb1c8b7..1ebc5421f 100644
--- a/.gitignore
+++ b/.gitignore
@@ -337,6 +337,7 @@ Makefile.in
 /lib/libguestfs.syms
 /lib/.libs/libguestfs.so
 /lib/libvirt-is-version
+/lib/local/libguestfs.pc
 /lib/stamp-guestfs.pod
 /lib/structs-compare.c
 /lib/structs-copy.c
diff --git a/configure.ac b/configure.ac
index 3a4d6c931..3971d30f6 100644
--- a/configure.ac
+++ b/configure.ac
@@ -276,6 +276,7 @@ AC_CONFIG_FILES([Makefile
                  java/examples/Makefile
                  lib/Makefile
                  lib/libguestfs.pc
+                 lib/local/libguestfs.pc
                  lua/Makefile
                  lua/examples/Makefile
                  make-fs/Makefile
diff --git a/lib/Makefile.am b/lib/Makefile.am
index e5df96fe2..4fef46826 100644
--- a/lib/Makefile.am
+++ b/lib/Makefile.am
@@ -47,6 +47,7 @@ EXTRA_DIST = \
 	$(BUILT_SOURCES) \
 	MAX_PROC_NR \
 	libguestfs.pc.in \
+	local/libguestfs.pc.in \
 	guestfs.pod
 
 include_HEADERS = guestfs.h
diff --git a/lib/local/libguestfs.pc.in b/lib/local/libguestfs.pc.in
new file mode 100644
index 000000000..b736cd671
--- /dev/null
+++ b/lib/local/libguestfs.pc.in
@@ -0,0 +1,36 @@
+# @configure_input@
+# Copyright (C) 2020 Red Hat Inc.
+#
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program; if not, write to the Free Software
+# Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+
+
+# Dummy pkg-config file which is used to allow out of tree packages to
+# be configured against the libguestfs tree without libguestfs needing
+# to be installed.
+#
+# Note if you are using the ./run script then you don't need to worry
+# about this because the script sets PKG_CONFIG_PATH correctly.
+
+prefix=@abs_top_builddir@
+exec_prefix=@abs_top_builddir@
+libdir=@abs_top_builddir@/lib/.libs
+includedir=@abs_top_srcdir@/lib
+
+Name: libguestfs
+Version: @VERSION@
+Description: libguestfs library for accessing and modifying VM images
+Requires:
+Cflags: -I${includedir}
+Libs: -L${libdir} -lguestfs @LIBS@
diff --git a/run.in b/run.in
index c734612fc..6896d5a2c 100755
--- a/run.in
+++ b/run.in
@@ -223,6 +223,11 @@ export G_DEBUG=gc-friendly
 random_val="$(@AWK@ 'BEGIN{srand(); print 1+int(255*rand())}' <
/dev/null)"
 export MALLOC_PERTURB_=$random_val
 
+# Allow dependent packages like virt-v2v to be compiled against
+# local libguestfs.
+prepend PKG_CONFIG_PATH "$b/lib/local"
+export PKG_CONFIG_PATH
+
 # Do we have libtool?  If we have it then we can use it to make
 # running valgrind simpler.  However don't depend on it.
 if libtool --help >/dev/null 2>&1; then
-- 
2.24.1

You have to use:
  ../libguestfs/run ./configure
  ../libguestfs/run make

Use of the second ../libguestfs/run against make is unfortunate but I
believe it's unavoidable due to the way that ocamlfind works.
---
 .gitignore        |  1 +
 ocaml/Makefile.am | 19 ++++++++++++++++++-
 run.in            |  2 ++
 3 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/.gitignore b/.gitignore
index 1ebc5421f..cdc90453c 100644
--- a/.gitignore
+++ b/.gitignore
@@ -379,6 +379,7 @@ Makefile.in
 /ocaml/examples/guestfs-ocaml.3
 /ocaml/examples/inspect_vm
 /ocaml/examples/stamp-guestfs-ocaml.pod
+/ocaml/guestfs
 /ocaml/guestfs-c-actions.c
 /ocaml/guestfs-c-errnos.c
 /ocaml/guestfs.ml
diff --git a/ocaml/Makefile.am b/ocaml/Makefile.am
index c85efee64..c02246270 100644
--- a/ocaml/Makefile.am
+++ b/ocaml/Makefile.am
@@ -197,4 +197,21 @@ install-data-hook:
 
 CLEANFILES += $(noinst_DATA) $(check_DATA)
 
-endif
+# This "tricks" ocamlfind into allowing us to compile other OCaml
+# programs against a locally compiled copy of the libguestfs sources.
+# ocamlfind needs to see a directory called ‘guestfs’ which contains
+# ‘META’.  The current directory is called ‘ocaml’, but if we make
+# this symlink then we can create the required directory structure.
+#
+# Note if you just want to use this, make sure you use
+# ‘../libguestfs/run make’ in your other program and everything should
+# just work.
+CLEANFILES += guestfs
+
+all-local: guestfs
+
+guestfs:
+	rm -f $@
+	ln -sf . $@
+
+endif HAVE_OCAML
diff --git a/run.in b/run.in
index 6896d5a2c..90552fb04 100755
--- a/run.in
+++ b/run.in
@@ -227,6 +227,8 @@ export MALLOC_PERTURB_=$random_val
 # local libguestfs.
 prepend PKG_CONFIG_PATH "$b/lib/local"
 export PKG_CONFIG_PATH
+prepend OCAMLPATH "$b/ocaml"
+export OCAMLPATH
 
 # Do we have libtool?  If we have it then we can use it to make
 # running valgrind simpler.  However don't depend on it.
-- 
2.24.1

On 3/10/20 10:05 AM, Richard W.M. Jones wrote:
> We use a similar trick to libvirt to allow external C programs that
> use libguestfs to be compiled against the built (but not installed)
> libguestfs with:
> 
>    ../libguestfs/run ./configure
>    make
> 
> What actually happens is we have a second pkg-config file
> (lib/local/libguestfs.pc) which points to the locally built
> libguestfs.  The ./run script sets up PKG_CONFIG_PATH to point to this
> directory.  Assuming that ./configure is using pkg-config/pkgconf and
> not some other half-baked solution it will pick up the libguestfs.pc
> file from here which will set CFLAGS and LIBS appropriately.
> ---
>   .gitignore                 |  1 +
>   configure.ac               |  1 +
>   lib/Makefile.am            |  1 +
>   lib/local/libguestfs.pc.in | 36 ++++++++++++++++++++++++++++++++++++
>   run.in                     |  5 +++++
>   5 files changed, 44 insertions(+)
> 
I like it. Should we do the same for libnbd's run script?

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

On 3/10/20 10:05 AM, Richard W.M. Jones wrote:
> You have to use:
>    ../libguestfs/run ./configure
>    ../libguestfs/run make
> 
> Use of the second ../libguestfs/run against make is unfortunate but I
> believe it's unavoidable due to the way that ocamlfind works.
Or even:

../libguestfs/run sh -c './configure && make'

But yes, the need to set the environment multiple times makes sense, 
even if it is unfortunate that 'make' is unable to rely solely on what 
was learned at configure-time.
> ---
>   .gitignore        |  1 +
>   ocaml/Makefile.am | 19 ++++++++++++++++++-
>   run.in            |  2 ++
>   3 files changed, 21 insertions(+), 1 deletion(-)
> 
-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org

On Tuesday, 10 March 2020 16:05:18 CET Richard W.M. Jones
wrote:
> We use a similar trick to libvirt to allow external C programs that
> use libguestfs to be compiled against the built (but not installed)
> libguestfs with:
> 
>   ../libguestfs/run ./configure
>   make
Or even more easily, covering also the OCaml usage:

  $ /path/to/libguestfs/run bash -i
  $ ./configure
  $ make
  $ [etc]
> What actually happens is we have a second pkg-config file
> (lib/local/libguestfs.pc) which points to the locally built
> libguestfs.  The ./run script sets up PKG_CONFIG_PATH to point to this
> directory.  Assuming that ./configure is using pkg-config/pkgconf and
> not some other half-baked solution it will pick up the libguestfs.pc
> file from here which will set CFLAGS and LIBS appropriately.
> ---
Seems OK, just one thing:
> +Name: libguestfs
> +Version: @VERSION@
> +Description: libguestfs library for accessing and modifying VM images
> +Requires:
> +Cflags: -I${includedir}
> +Libs: -L${libdir} -lguestfs @LIBS@
Not sure where this $LIBS variable comes from, as it is empty (even the
installed libguestfs.pc has this).

I'd drop it from this patch, and I will send a patch for the installed
libguestfs.pc.in.

-- 
Pino Toscano

On Tuesday, 10 March 2020 16:05:19 CET Richard W.M. Jones
wrote:
> You have to use:
>   ../libguestfs/run ./configure
>   ../libguestfs/run make
> 
> Use of the second ../libguestfs/run against make is unfortunate but I
> believe it's unavoidable due to the way that ocamlfind works.
Or a simplier:

  $ /path/to/libguestfs/run bash -i
  $ ./configure
  $ make
  $ [etc]
> ---
>  .gitignore        |  1 +
>  ocaml/Makefile.am | 19 ++++++++++++++++++-
>  run.in            |  2 ++
>  3 files changed, 21 insertions(+), 1 deletion(-)
> 
> diff --git a/.gitignore b/.gitignore
> index 1ebc5421f..cdc90453c 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -379,6 +379,7 @@ Makefile.in
>  /ocaml/examples/guestfs-ocaml.3
>  /ocaml/examples/inspect_vm
>  /ocaml/examples/stamp-guestfs-ocaml.pod
> +/ocaml/guestfs
>  /ocaml/guestfs-c-actions.c
>  /ocaml/guestfs-c-errnos.c
>  /ocaml/guestfs.ml
> diff --git a/ocaml/Makefile.am b/ocaml/Makefile.am
> index c85efee64..c02246270 100644
> --- a/ocaml/Makefile.am
> +++ b/ocaml/Makefile.am
> @@ -197,4 +197,21 @@ install-data-hook:
>  
>  CLEANFILES += $(noinst_DATA) $(check_DATA)
>  
> -endif
> +# This "tricks" ocamlfind into allowing us to compile other
OCaml
> +# programs against a locally compiled copy of the libguestfs sources.
> +# ocamlfind needs to see a directory called ‘guestfs’ which contains
> +# ‘META’.  The current directory is called ‘ocaml’, but if we make
> +# this symlink then we can create the required directory structure.
> +#
> +# Note if you just want to use this, make sure you use
> +# ‘../libguestfs/run make’ in your other program and everything should
> +# just work.
> +CLEANFILES += guestfs
> +
> +all-local: guestfs
> +
> +guestfs:
> +	rm -f $@
> +	ln -sf . $@
The '.' might be better replaced by $(srcdir) instead, although it will
only matter when building libguestfs with builddir!=srcdir, and then
anything against that uninstalled libguestfs.

The rest LGTM.

-- 
Pino Toscano