Libguestfs - Oct 2021 - [PATCH 0/3] clean up Yara (version) dependency

Libguestfs now depends (optionally) on Yara >= 4.0.0. Make this explicit
in the build configuration and the build documentation.

Thanks,
Laszlo

Laszlo Ersek (3):
  build: fix the pkg-config identifier of the (optional) Yara library
  build: eliminate the AC_CHECK_LIB / AC_CHECK_HEADER tests for Yara
  build, docs: spell out minimum version (4.0.0) for the (optional) Yara
    lib

 docs/guestfs-building.pod |  2 +-
 m4/guestfs-daemon.m4      | 11 ++---------
 2 files changed, 3 insertions(+), 10 deletions(-)


base-commit: e597fc5317e018c259c75eb475cf6668e07236d1
-- 
2.19.1.3.g30247aa5d201

The upstream Yara project has always provided its "libyara/yara.pc.in"
file with "Name: yara" -- ever since its introduction in commit
334bd1a671ca ("Add support for pkg-config", 2015-01-08).

In spite of this, when the (optional) Yara dependency was added to
libguestfs in commit 2e24129da376 ("appliance: add yara dependency",
2017-05-02), PKG_CHECK_MODULES was invoked with [libyara] as
list-of-modules.

(That was clearly a bug. I'm unsure what Debian calls their Yara
pkg-config module, but calling it anything else than "yara" would be a
distribution bug: upstream projects provide pkg-config files specifically
so that dependent projects can find their dependencies *regardless of
distribution*.)

As a consequence, on Fedora today, the PKG_CHECK_MODULES macro always
fails, and only the AC_CHECK_LIB / AC_CHECK_HEADER branch finds Yara.

In a subsequent patch, we'll want to add a version requirement to the
PKG_CHECK_MODULES macro invocation, so at first, fix the pkg-config
identifier of Yara.

Fixes: 2e24129da37656706b5a1d3b6bc83d4c089740bb
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 m4/guestfs-daemon.m4 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/m4/guestfs-daemon.m4 b/m4/guestfs-daemon.m4
index 1728249a5fb7..0790f8848249 100644
--- a/m4/guestfs-daemon.m4
+++ b/m4/guestfs-daemon.m4
@@ -134,7 +134,7 @@ AC_CHECK_LIB([tsk],[tsk_version_print],[
 ],[AC_MSG_WARN([The Sleuth Kit library (libtsk) not found])])
 
 dnl yara library (optional)
-PKG_CHECK_MODULES([YARA], [libyara],[
+PKG_CHECK_MODULES([YARA], [yara],[
     AC_SUBST([YARA_CFLAGS])
     AC_SUBST([YARA_LIBS])
     AC_DEFINE([HAVE_YARA],[1],[yara library found at compile time.])
-- 
2.19.1.3.g30247aa5d201

Eliminate the AC_CHECK_LIB / AC_CHECK_HEADER tests for Yara, for the
following reasons:

- Upstream Yara has provided a pkg-config file since 2015, so the
  (now-fixed) pkg-config check should always find it, without the
  AC_CHECK_LIB / AC_CHECK_HEADER fallback branch.

- In a subsequent patch, we'll want to test for the incompatible Yara API
  changes described at
 
<https://github.com/VirusTotal/yara/wiki/Backward-incompatible-changes-in-YARA-4.0-API>.

  That's easy to do with pkg-config, but impossible with AC_CHECK_*,
  without a custom test. Namely, both AC_CHECK_DECLS and AC_CHECK_TYPES
  appear unable to check the parameter list of a function pointer typedef
  (namely YR_CALLBACK_FUNC and YR_COMPILER_CALLBACK_FUNC). And writing a
  dedicated test for this is overkill.

Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 m4/guestfs-daemon.m4 | 9 +--------
 1 file changed, 1 insertion(+), 8 deletions(-)

diff --git a/m4/guestfs-daemon.m4 b/m4/guestfs-daemon.m4
index 0790f8848249..316a811d30a9 100644
--- a/m4/guestfs-daemon.m4
+++ b/m4/guestfs-daemon.m4
@@ -138,11 +138,4 @@ PKG_CHECK_MODULES([YARA], [yara],[
     AC_SUBST([YARA_CFLAGS])
     AC_SUBST([YARA_LIBS])
     AC_DEFINE([HAVE_YARA],[1],[yara library found at compile time.])
-],[
-    AC_CHECK_LIB([yara],[yr_initialize],[
-        AC_CHECK_HEADER([yara.h],[
-            AC_SUBST([YARA_LIBS], [-lyara])
-            AC_DEFINE([HAVE_YARA], [1], [Define to 1 if Yara library is
available.])
-        ], [])
-    ],[AC_MSG_WARN([Yara library not found])])
-])
+],[AC_MSG_WARN([Yara library not found])])
-- 
2.19.1.3.g30247aa5d201

Commit e597fc5317e0 ("daemon/yara: fix undefined behavior due to Yara 4.0
API changes", 2021-10-12) prevents the daemon from using such a Yara
version that precedes 4.0.0.

If only yara < 4 is found, treat the library as absent, rather than
attempting and failing to compile the yara module of the daemon. Note the
version requirement in the documentation too.

Suggested-by: Eric Blake <eblake at redhat.com>
Suggested-by: Richard W.M. Jones <rjones at redhat.com>
Signed-off-by: Laszlo Ersek <lersek at redhat.com>
---
 docs/guestfs-building.pod | 2 +-
 m4/guestfs-daemon.m4      | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/docs/guestfs-building.pod b/docs/guestfs-building.pod
index 1f872700e367..803b89fd5ea6 100644
--- a/docs/guestfs-building.pod
+++ b/docs/guestfs-building.pod
@@ -387,7 +387,7 @@ Optional.  For tab-completion of commands in bash.
 
 Optional.  Library for filesystem forensics analysis.
 
-=item yara
+=item yara E<ge> 4.0.0
 
 Optional.  Tool for categorizing files based on their content.
 
diff --git a/m4/guestfs-daemon.m4 b/m4/guestfs-daemon.m4
index 316a811d30a9..4dec4fa67995 100644
--- a/m4/guestfs-daemon.m4
+++ b/m4/guestfs-daemon.m4
@@ -134,7 +134,7 @@ AC_CHECK_LIB([tsk],[tsk_version_print],[
 ],[AC_MSG_WARN([The Sleuth Kit library (libtsk) not found])])
 
 dnl yara library (optional)
-PKG_CHECK_MODULES([YARA], [yara],[
+PKG_CHECK_MODULES([YARA], [yara >= 4.0.0],[
     AC_SUBST([YARA_CFLAGS])
     AC_SUBST([YARA_LIBS])
     AC_DEFINE([HAVE_YARA],[1],[yara library found at compile time.])
-- 
2.19.1.3.g30247aa5d201