[dm-devel] [PATCH v2 2/3] libmutipath: don't close fd on dm_lib_release

[Benjamin Marzinski]

If dm_hold_control_open() isn't set, when dm_lib_release() is called, it
will close the control fd. The control fd will get re-opened on the next
dm_task_run() call, but if there is a dm_task_run() call already
in progress in another thread, it can fail. Since many of the
device-mapper callouts happen with the vecs lock held, this wasn't too
noticeable, but there is code that calls dm_task_run() without the
vecs lock held, notably the dmevent waiter code.

Since, as Martin pointed out, dm_hold_control_open() hasn't always
existed in libdevmapper, check if it's supported on compilation,
and update the version requirements if so.

Signed-off-by: Benjamin Marzinski <bmarzins at redhat.com>
---
 libmultipath/Makefile    | 4 ++++
 libmultipath/devmapper.c | 7 ++++++-
 2 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/libmultipath/Makefile b/libmultipath/Makefile
index e5651e49..ad690a49 100644
--- a/libmultipath/Makefile
+++ b/libmultipath/Makefile
@@ -36,6 +36,10 @@ ifneq ($(call check_func,dm_task_deferred_remove,/usr/include/libdevmapper.h),0)
 	CFLAGS += -DLIBDM_API_DEFERRED
 endif
 
+ifneq ($(call check_func,dm_hold_control_dev,/usr/include/libdevmapper.h),0)
+	CFLAGS += -DLIBDM_API_HOLD_CONTROL
+endif
+
 OBJS = memory.o parser.o vector.o devmapper.o callout.o \
 	hwtable.o blacklist.o util.o dmparser.o config.o \
 	structs.o discovery.o propsel.o dict.o \
diff --git a/libmultipath/devmapper.c b/libmultipath/devmapper.c
index bed8ddc6..13a1cf53 100644
--- a/libmultipath/devmapper.c
+++ b/libmultipath/devmapper.c
@@ -108,7 +108,9 @@ dm_lib_prereq (void)
 {
 	char version[64];
 	int v[3];
-#if defined(LIBDM_API_DEFERRED)
+#if defined(LIBDM_API_HOLD_CONTROL)
+	int minv[3] = {1, 2, 111};
+#elif defined(LIBDM_API_DEFERRED)
 	int minv[3] = {1, 2, 89};
 #elif defined(DM_SUBSYSTEM_UDEV_FLAG0)
 	int minv[3] = {1, 2, 82};
@@ -254,6 +256,9 @@ void libmp_dm_init(void)
 	memcpy(conf->version, version, sizeof(version));
 	put_multipath_config(conf);
 	dm_init(verbosity);
+#ifdef LIBDM_API_HOLD_CONTROL
+	dm_hold_control_dev(1);
+#endif
 	dm_udev_set_sync_support(libmp_dm_udev_sync);
 }
 
-- 
2.17.2