[libvirt] [PATCH] configure: Fix devlink detection

[Ján Tomko]

On Tue, Sep 19, 2017 at 10:31:31AM +0200, Andrea Bolognani wrote:
>There are some quirks to detecting whether devlink support can be
>activated due to symbols being renamed between Linux versions.
>
>Make detection more robust so that the code can once again compile
>on RHEL 7 and others.
>
>Signed-off-by: Andrea Bolognani <abologna at redhat.com>
>---
> configure.ac         | 26 ++++++++++++++++++++++----
> src/util/virnetdev.c |  5 +++++
> 2 files changed, 27 insertions(+), 4 deletions(-)
>
>diff --git a/configure.ac b/configure.ac
>index c9509c7f9..6f03152b4 100644
>--- a/configure.ac
>+++ b/configure.ac
>@@ -632,12 +632,30 @@ dnl check for kernel headers required by devlink
> dnl
> if test "$with_linux" = "yes"; then
>     AC_CHECK_HEADERS([linux/devlink.h])
>-    AC_CHECK_DECLS([DEVLINK_GENL_VERSION, DEVLINK_GENL_NAME, DEVLINK_ATTR_MAX, DEVLINK_CMD_ESWITCH_GET, DEVLINK_ATTR_BUS_NAME, DEVLINK_ATTR_DEV_NAME, DEVLINK_ATTR_ESWITCH_MODE, DEVLINK_ESWITCH_MODE_SWITCHDEV],
>-                   [AC_DEFINE([HAVE_DECL_DEVLINK],
>-                              [1],
>-                              [whether devlink declarations are available])],
>+
>+    dnl DEVLINK_CMD_ESWITCH_MODE_GET was introduced in Linux 4.8, but Linux
>+    dnl 4.11 renamed it to DEVLINK_CMD_ESWITCH_GET. We can use either, but
>+    dnl we need at least one of them to be available
>+    have_eswitch_get=0

We should not be using deprecated constant names in new code.

>+    AC_CHECK_DECLS([DEVLINK_CMD_ESWITCH_GET, DEVLINK_CMD_ESWITCH_MODE_GET],
>+                   [have_eswitch_get=1],
>+                   [],
>+                   [[#include <linux/devlink.h>]])
>+
>+    dnl We use a bunch of other symbols as well
>+    have_all_others=1

>+    AC_CHECK_DECLS([DEVLINK_GENL_VERSION, DEVLINK_GENL_NAME, DEVLINK_ATTR_MAX, DEVLINK_ATTR_BUS_NAME, DEVLINK_ATTR_DEV_NAME,

All these constants were introduced by commit bfcd3a4661 along with the
devlink infractructure. Having any of them is a sufficient witness for
HAVE_DECL_DEVLINK and pointless to check here.

As for these two:
DEVLINK_ATTR_ESWITCH_MODE, DEVLINK_ESWITCH_MODE_SWITCHDEV],

we only need to check for ESWITCH_MODE. If there are any modes to
check for, SWITCHDEV should be one of the known ones.

>                    [],
>+                   [have_all_others=0],
>                    [[#include <linux/devlink.h>]])
>+
>+    dnl If we have at least one variation of DEVLINK_CMD_ESWITCH_GET *and*
>+    dnl all other symbols, then we can enable the devlink code
>+    if test have_eswitch_get = 1 && test have_all_others = 1; then
>+        AC_DEFINE_UNQUOTED([HAVE_DECL_DEVLINK],
>+                           [1],
>+                           [whether devlink declarations are available])
>+    fi
> fi
>
> dnl Allow perl/python overrides
>diff --git a/src/util/virnetdev.c b/src/util/virnetdev.c
>index 040693925..1e0a257e1 100644
>--- a/src/util/virnetdev.c
>+++ b/src/util/virnetdev.c
>@@ -3245,7 +3245,12 @@ virNetDevSwitchdevFeature(const char *ifname,
>     if (!(gmsgh = virNetDevPutExtraHeader(nlmsg_hdr(nl_msg), sizeof(struct genlmsghdr))))
>         goto cleanup;
>
>+#if HAVE_DEVLINK_CMD_ESWITCH_GET
>     gmsgh->cmd = DEVLINK_CMD_ESWITCH_GET;
>+#elif HAVE_DEVLINK_CMD_ESWITCH_MODE_GET
>+    gmsgh->cmd = DEVLINK_CMD_ESWITCH_MODE_GET;

We really don't need to litter the code with obsolete constants.

Jan

>+#endif
>+
>     gmsgh->version = DEVLINK_GENL_VERSION;
>
>     pci_device_ptr = pfname ? virNetDevGetPCIDevice(pfname) :
>-- 
>2.13.5
>
>--
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