LVM2: fix lvmetad udev rules for CHANGE events

index bd75fc8..38687f4 100644
@@ -88,6 +88,23 @@ LABEL="lvm_scan"
 #  loop  |          |      X      |       X*       |                   |
 #  other |    X     |             |       X        |                   |   X
 ENV{SYSTEMD_READY}="1"
-(PVSCAN_RULE)
+
+# The method for invoking pvscan is selected at build time with the option
+# --(enable|disable)-udev-systemd-background-jobs to "configure".
+# On modern distributions with recent systemd, it's "systemd_background";
+# on others, "direct_pvscan".
+GOTO="(PVSCAN_RULE)"
+
+LABEL="systemd_background"
+
+ACTION!="remove", ENV{LVM_PV_GONE}=="1", RUN+="(BINDIR)/systemd-run (LVM_EXEC)/lvm pvscan --cache $major:$minor", GOTO="lvm_end"
+ENV{SYSTEMD_ALIAS}="/dev/block/$major:$minor"
+ENV{ID_MODEL}="LVM PV $env{ID_FS_UUID_ENC} on /dev/$name"
+ENV{SYSTEMD_WANTS}+="lvm2-pvscan@$major:$minor.service"
+GOTO="lvm_end"
+
+LABEL="direct_pvscan"
+
+RUN+="(LVM_EXEC)/lvm pvscan --background --cache --activate ay --major $major --minor $minor", ENV{LVM_SCANNED}="1"
 
 LABEL="lvm_end"

index c498aa8..9b2e2c3 100644
@@ -25,6 +25,7 @@ endif
 
 DM_DIR=$(shell $(GREP) "\#define DM_DIR" $(top_srcdir)/libdm/misc/dm-ioctl.h | $(AWK) '{print $$3}')
 
+BINDIR=@bindir@
 ifeq ("@UDEV_RULE_EXEC_DETECTION@", "yes")
 SBIN=\$$env{DM_SBIN_PATH}
 DM_EXEC_RULE=ENV{DM_SBIN_PATH}=\"\/sbin\"\\nTEST!=\"\$$env{DM_SBIN_PATH}\/dmsetup\", ENV{DM_SBIN_PATH}=\"\/usr\/sbin\"

@@ -46,13 +47,13 @@ BLKID_RULE=IMPORT{program}=\"${SBIN}\/blkid -o udev -p \$$tempnode\"
 endif
 
 ifeq ("@UDEV_SYSTEMD_BACKGROUND_JOBS@", "yes")
-PVSCAN_RULE=ACTION\!=\"remove\", ENV{LVM_PV_GONE}==\"1\", RUN\+=\"@bindir@/systemd-run $(LVM_EXEC)\/lvm pvscan --cache \$$major\:\$$minor\", GOTO=\"lvm_end\"\nENV{SYSTEMD_ALIAS}=\"\/dev\/block\/\$$major:\$$minor\"\nENV{ID_MODEL}=\"LVM PV \$$env{ID_FS_UUID_ENC} on \/dev\/\$$name\"\nENV{SYSTEMD_WANTS}\+=\"lvm2-pvscan@\$$major:\$$minor.service\"
+PVSCAN_RULE=systemd_background
 else
-PVSCAN_RULE=RUN\+\=\"$(LVM_EXEC)/lvm pvscan --background --cache --activate ay --major \$$major --minor \$$minor\", ENV{LVM_SCANNED}=\"1\"
+PVSCAN_RULE=direct_pvscan
 endif
 
 %.rules: $(srcdir)/%.rules.in
-	$(SED) -e "s+(DM_DIR)+$(DM_DIR)+;s+(BLKID_RULE)+$(BLKID_RULE)+;s+(PVSCAN_RULE)+$(PVSCAN_RULE)+;s+(DM_EXEC_RULE)+$(DM_EXEC_RULE)+;s+(DM_EXEC)+$(DM_EXEC)+;s+(LVM_EXEC_RULE)+$(LVM_EXEC_RULE)+;s+(LVM_EXEC)+$(LVM_EXEC)+;" $< >$@
+	$(SED) -e "s+(DM_DIR)+$(DM_DIR)+;s+(BINDIR)+$(BINDIR)+;s+(BLKID_RULE)+$(BLKID_RULE)+;s+(PVSCAN_RULE)+$(PVSCAN_RULE)+;s+(DM_EXEC_RULE)+$(DM_EXEC_RULE)+;s+(DM_EXEC)+$(DM_EXEC)+;s+(LVM_EXEC_RULE)+$(LVM_EXEC_RULE)+;s+(LVM_EXEC)+$(LVM_EXEC)+;" $< >$@
 
 %_install: %.rules
 	$(INSTALL_DATA) -D $< $(udevdir)/$(<F)

index 38687f4..2ff8ddc 100644
@@ -68,25 +68,15 @@ ACTION=="change", ENV{LVM_LOOP_PV_ACTIVATED}!="1", TEST=="loop/backing_file", EN
 ENV{LVM_LOOP_PV_ACTIVATED}!="1", ENV{SYSTEMD_READY}="0"
 GOTO="lvm_end"
 
-# If the PV is not a special device listed above, scan only after device addition (ADD event)
+# If the PV is not a special device listed above, scan only if necessary.
+# For "direct_pvscan" mode (see below), this means run rules only an ADD events.
+# For "systemd_background" mode, systemd takes care of this by activating
+# the [email protected] only once.
 LABEL="next"
-ACTION!="add", GOTO="lvm_end"
+ACTION!="(PVSCAN_ACTION)", GOTO="lvm_end"
 
 LABEL="lvm_scan"
 
-# The table below summarises the situations in which we reach the LABEL="lvm_scan".
-# Marked by X, X* means only if the special dev is properly set up.
-# The artificial ADD is supported for coldplugging. We avoid running the pvscan
-# on artificial CHANGE so there's no unexpected autoactivation when WATCH rule fires.
-# N.B. MD and loop never actually  reaches lvm_scan on REMOVE as the PV label is gone
-# within a CHANGE event (these are caught by the "LVM_PV_GONE" rule at the beginning).
-#
-#        | real ADD | real CHANGE | artificial ADD | artificial CHANGE | REMOVE
-# =============================================================================
-#  DM    |          |      X      |       X*       |                   |   X
-#  MD    |          |      X      |       X*       |                   |
-#  loop  |          |      X      |       X*       |                   |
-#  other |    X     |             |       X        |                   |   X
 ENV{SYSTEMD_READY}="1"
 
 # The method for invoking pvscan is selected at build time with the option

@@ -97,6 +87,27 @@ GOTO="(PVSCAN_RULE)"
 
 LABEL="systemd_background"
 
+# The table below summarises the situations in which we reach the LABEL="lvm_scan"
+# in the "systemd_background" case.
+# Marked by X, X* means only if the special dev is properly set up.
+# The artificial ADD is supported for coldplugging. We avoid running the pvscan
+# on artificial CHANGE so there's no unexpected autoactivation when WATCH rule fires.
+# N.B. MD and loop never actually  reaches lvm_scan on REMOVE as the PV label is gone
+# within a CHANGE event (these are caught by the "LVM_PV_GONE" rule at the beginning).
+#
+# In this case, we simply set up the dependency between the device and the pvscan
+# job using SYSTEMD_ALIAS (which sets up a simplified device identifier that
+# allows using "BindsTo" in the sytemd unit file) and SYSTEMD_WANTS (which tells
+# systemd to start the pvscan job once the device is ready).
+# We need to set these variables for both "add" and "change" events, otherwise
+# systemd may loose information about the device/unit dependencies.
+#
+#        | real ADD | real CHANGE | artificial ADD | artificial CHANGE | REMOVE
+# =============================================================================
+#  DM    |          |      X      |       X*       |                   |   X
+#  MD    |          |      X      |       X*       |                   |
+#  loop  |          |      X      |       X*       |                   |
+#  other |    X     |      X      |       X        |                   |   X
 ACTION!="remove", ENV{LVM_PV_GONE}=="1", RUN+="(BINDIR)/systemd-run (LVM_EXEC)/lvm pvscan --cache $major:$minor", GOTO="lvm_end"
 ENV{SYSTEMD_ALIAS}="/dev/block/$major:$minor"
 ENV{ID_MODEL}="LVM PV $env{ID_FS_UUID_ENC} on /dev/$name"

@@ -105,6 +116,21 @@ GOTO="lvm_end"
 
 LABEL="direct_pvscan"
 
+# The table below summarises the situations in which we reach the LABEL="lvm_scan"
+# for the "direct_pvscan" case.
+# Marked by X, X* means only if the special dev is properly set up.
+# The artificial ADD is supported for coldplugging. We avoid running the pvscan
+# on artificial CHANGE so there's no unexpected autoactivation when WATCH rule fires.
+#
+# In this case, we need to make sure that pvscan is not invoked spuriously, therefore
+# we invoke it only for "add" events for "other" devices.
+#
+#        | real ADD | real CHANGE | artificial ADD | artificial CHANGE | REMOVE
+# =============================================================================
+#  DM    |          |      X      |       X*       |                   |   X
+#  MD    |          |      X      |       X*       |                   |
+#  loop  |          |      X      |       X*       |                   |
+#  other |    X     |             |       X        |                   |   X
 RUN+="(LVM_EXEC)/lvm pvscan --background --cache --activate ay --major $major --minor $minor", ENV{LVM_SCANNED}="1"
 
 LABEL="lvm_end"

index 9b2e2c3..6f57d46 100644
@@ -48,12 +48,14 @@ endif
 
 ifeq ("@UDEV_SYSTEMD_BACKGROUND_JOBS@", "yes")
 PVSCAN_RULE=systemd_background
+PVSCAN_ACTION=add|change
 else
 PVSCAN_RULE=direct_pvscan
+PVSCAN_ACTION=add
 endif
 
 %.rules: $(srcdir)/%.rules.in
-	$(SED) -e "s+(DM_DIR)+$(DM_DIR)+;s+(BINDIR)+$(BINDIR)+;s+(BLKID_RULE)+$(BLKID_RULE)+;s+(PVSCAN_RULE)+$(PVSCAN_RULE)+;s+(DM_EXEC_RULE)+$(DM_EXEC_RULE)+;s+(DM_EXEC)+$(DM_EXEC)+;s+(LVM_EXEC_RULE)+$(LVM_EXEC_RULE)+;s+(LVM_EXEC)+$(LVM_EXEC)+;" $< >$@
+	$(SED) -e "s+(DM_DIR)+$(DM_DIR)+;s+(BINDIR)+$(BINDIR)+;s+(BLKID_RULE)+$(BLKID_RULE)+;s+(PVSCAN_RULE)+$(PVSCAN_RULE)+;s+(PVSCAN_ACTION)+$(PVSCAN_ACTION)+;s+(DM_EXEC_RULE)+$(DM_EXEC_RULE)+;s+(DM_EXEC)+$(DM_EXEC)+;s+(LVM_EXEC_RULE)+$(LVM_EXEC_RULE)+;s+(LVM_EXEC)+$(LVM_EXEC)+;" $< >$@
 
 %_install: %.rules
 	$(INSTALL_DATA) -D $< $(udevdir)/$(<F)