[libvirt] [PATCH] build: avoid -lgcrypt with newer gnutls

[Eric Blake]

https://bugzilla.redhat.com/show_bug.cgi?id=951637

Newer gnutls uses nettle, rather than gcrypt, which is a lot nicer
regarding initialization.  Yet we were unconditionally initializing
gcrypt even when gnutls wouldn't be using it, and having two crypto
libraries linked into libvirt.so is pointless.

The ldd probe in configure borrows from our libnl-1 vs. libnl-3 code.

* configure.ac (WITH_GNUTLS): Probe whether to add -lgcrypt, and
define a witness WITH_GNUTLS_GCRYPT.
* src/libvirt.c (virTLSMutexInit, virTLSMutexDestroy)
(virTLSMutexLock, virTLSMutexUnlock, virTLSThreadImpl)
(virGlobalInit): Honor the witness.
* libvirt.spec.in (BuildRequires): Make gcrypt usage conditional,
no longer needed in Fedora 19.

Signed-off-by: Eric Blake <eblake at redhat.com>
---

Tested with 'ldd src/.libs/libvirt.so | grep -E "(gcry|net|tls)"':
- on RHEL 6.4 and Fedora 18, pre- and post-patch remain unchanged
(use of just libgnutls/libgcrypt)
- on Fedora 19, pre-patch linked against libgnutls, libgcrypt, and
libnettle, post-patch linked against just libgnutls and libnettle

This should probably go in for 1.1.1, but it's not a build-breaker
so it needs review.

 configure.ac    | 27 +++++++++++++++++++++------
 libvirt.spec.in |  2 ++
 src/libvirt.c   | 10 ++++++----
 3 files changed, 29 insertions(+), 10 deletions(-)

diff --git a/configure.ac b/configure.ac
index cc9942a..de209e2 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1098,13 +1098,28 @@ if test "x$with_gnutls" != "xno"; then
       AC_MSG_ERROR([You must install the GnuTLS library in order to compile and run libvirt])
     fi
   else
-    dnl Not all versions of gnutls include -lgcrypt, and so we add
-    dnl it explicitly for the calls to gcry_control/check_version
-    GNUTLS_LIBS="$GNUTLS_LIBS -lgcrypt"

-    dnl We're not using gcrypt deprecated features so define
-    dnl GCRYPT_NO_DEPRECATED to avoid deprecated warnings
-    GNUTLS_CFLAGS="$GNUTLS_CFLAGS -DGCRYPT_NO_DEPRECATED"
+    dnl If gnutls linked against -lgcrypt, then we must initialize gcrypt
+    dnl prior to using gnutls.  Newer versions of gnutls use -lnettle, in
+    dnl which case we don't want to drag in gcrypt ourselves.
+    gnutls_ldd=
+    for dir in /usr/lib64 /usr/lib /usr/lib/*-linux-gnu*; do
+        if test -f $dir/libgnutls.so; then
+            gnutls_ldd=`(ldd $dir/libgnutls.so) 2>&1`
+            break
+        fi
+    done
+    case $gnutls_ldd in
+    '' | *libgcrypt.so*)
+        GNUTLS_LIBS="$GNUTLS_LIBS -lgcrypt"
+	dnl We're not using gcrypt deprecated features so define
+        dnl GCRYPT_NO_DEPRECATED to avoid deprecated warnings
+        GNUTLS_CFLAGS="$GNUTLS_CFLAGS -DGCRYPT_NO_DEPRECATED"
+	AC_DEFINE_UNQUOTED([WITH_GNUTLS_GCRYPT], 1,
+          [whether GNUTLS uses gcrypt])
+	;;
+    *) ;; # Assume no gcrypt usage
+    esac

     dnl gnutls 3.x moved some declarations to a new header
     AC_CHECK_HEADERS([gnutls/crypto.h], [], [], [[
diff --git a/libvirt.spec.in b/libvirt.spec.in
index e0e0004..4320281 100644
--- a/libvirt.spec.in
+++ b/libvirt.spec.in
@@ -422,7 +422,9 @@ BuildRequires: readline-devel
 BuildRequires: ncurses-devel
 BuildRequires: gettext
 BuildRequires: libtasn1-devel
+%if (0%{?rhel} && 0%{?rhel} < 7) || (0%{?fedora} && 0%{?fedora} < 19)
 BuildRequires: libgcrypt-devel
+%endif
 BuildRequires: gnutls-devel
 BuildRequires: libattr-devel
 %if %{with_libvirtd}
diff --git a/src/libvirt.c b/src/libvirt.c
index 444c1c3..9775b97 100644
--- a/src/libvirt.c
+++ b/src/libvirt.c
@@ -55,7 +55,9 @@
 #include "intprops.h"
 #include "virconf.h"
 #if WITH_GNUTLS
-# include <gcrypt.h>
+# if WITH_GNUTLS_GCRYPT
+#  include <gcrypt.h>
+# endif
 # include "rpc/virnettlscontext.h"
 #endif
 #include "vircommand.h"
@@ -270,7 +272,7 @@ winsock_init(void)
 #endif


-#ifdef WITH_GNUTLS
+#ifdef WITH_GNUTLS_GCRYPT
 static int virTLSMutexInit(void **priv)
 {
     virMutexPtr lock = NULL;
@@ -323,7 +325,7 @@ static struct gcry_thread_cbs virTLSThreadImpl = {
     virTLSMutexUnlock,
     NULL, NULL, NULL, NULL, NULL, NULL, NULL, NULL
 };
-#endif
+#endif /* WITH_GNUTLS_GCRYPT */

 /* Helper macros to implement VIR_DOMAIN_DEBUG using just C99.  This
  * assumes you pass fewer than 15 arguments to VIR_DOMAIN_DEBUG, but
@@ -407,7 +409,7 @@ virGlobalInit(void)
         virErrorInitialize() < 0)
         goto error;

-#ifdef WITH_GNUTLS
+#ifdef WITH_GNUTLS_GCRYPT
     /*
      * This sequence of API calls it copied exactly from
      * gnutls 2.12.23 source lib/gcrypt/init.c, with
-- 
1.8.3.1