Re: [libvirt] [PATCH v2] util: Fix configure.ac check for DEVLINK_CMD_ESWITCH_GET

Turns out the mechanism of providing multiple definitions to check via AC_CHECK_DECLS in order to determine whether HAVE_DECL_DEVLINK should be set resulted in a false positive since as long as one of the defs was true, then the HAVE_DECL_DEVLINK got defined. But we cannot just check for the symbol we most care about due to a complication in a kernel 4.11 change that altered the name of the symbol from DEVLINK_CMD_ESWITCH_MODE_GET to DEVLINK_CMD_ESWITCH_GET in the newer kernel and added a #define for the former name with an ominous comment/caveat that the old format is obsolete should never be used. However, if we only looked for the new symbol, that would leave kernels 4.8 through 4.10 unable to use the command even though it exists under an old name. So, rather than checking for whether the devlink.h on the system has multiple symbols, let's only check for whether the command we want is defined. This patch checks for both symbol names in order to allow usage and then adds a check to see if the new name doesn't exist after linux/devlink.h is include, then to use #define of the new name to the old name - essentially the reverse logic that the 4.11 header file has. Note that we do not need to check for other symbols as well since they already existed prior to when the various ESWITCH symbols were added. Other defintions include DEVLINK_GENL_VERSION, DEVLINK_GENL_NAME, DEVLINK_ATTR_MAX, DEVLINK_ATTR_BUS_NAME, and DEVLINK_ATTR_DEV_NAME. The DEVLINK_ATTR_ESWITCH_MODE and DEVLINK_ESWITCH_MODE_SWITCHDEV were added at the same time as DEVLINK_CMD_ESWITCH_MODE_GET, but it's only DEVLINK_CMD_ESWITCH_MODE_GET that changed in 4.11. Signed-off-by: John Ferlan <jferlan(a)redhat.com&gt; --- v1: https://www.redhat.com/archives/libvir-list/2017-September/msg00543.html Just to make it official - here's what I described in the v1 followup which got the ACK if comment from Andrea: https://www.redhat.com/archives/libvir-list/2017-September/msg00591.html Still, I won't push this yet until it too gets an official blessing. configure.ac | 8 ++++++-- src/util/virnetdev.c | 3 +++ 2 files changed, 9 insertions(+), 2 deletions(-)