activation: Add "degraded" activation mode

Currently, we have two modes of activation, an unnamed nominal mode
(which I will refer to as "complete") and "partial" mode.  The
"complete" mode requires that a volume group be 'complete' - that
is, no missing PVs.  If there are any missing PVs, no affected LVs
are allowed to activate - even RAID LVs which might be able to
tolerate a failure.  The "partial" mode allows anything to be
activated (or at least attempted).  If a non-redundant LV is
missing a portion of its addressable space due to a device failure,
it will be replaced with an error target.  RAID LVs will either
activate or fail to activate depending on how badly their
redundancy is compromised.

This patch adds a third option, "degraded" mode.  This mode can
be selected via the '--activationmode {complete|degraded|partial}'
option to lvchange/vgchange.  It can also be set in lvm.conf.
The "degraded" activation mode allows RAID LVs with a sufficient
level of redundancy to activate (e.g. a RAID5 LV with one device
failure, a RAID6 with two device failures, or RAID1 with n-1
failures).  RAID LVs with too many device failures are not allowed
to activate - nor are any non-redundant LVs that may have been
affected.  This patch also makes the "degraded" mode the default
activation mode.

The degraded activation mode does not yet work in a cluster.  A
new cluster lock flag (LCK_DEGRADED_MODE) will need to be created
to make that work.  Currently, there is limited space for this
extra flag and I am looking for possible solutions.  One possible
solution is to usurp LCK_CONVERT, as it is not used.  When the
locking_type is 3, the degraded mode flag simply gets dropped and
the old ("complete") behavior is exhibited.

1 files changed, 27 insertions, 1 deletions

diff --git a/tools/lvmcmdline.c b/tools/lvmcmdline.c
index 780e9d0a5..fc51c4a7a 100644
--- a/tools/lvmcmdline.c
+++ b/tools/lvmcmdline.c
@@ -866,6 +866,8 @@ int version(struct cmd_context *cmd __attribute__((unused)),
 
 static int _get_settings(struct cmd_context *cmd)
 {
+	const char *activation_mode;
+
 	cmd->current_settings = cmd->default_settings;
 
 	if (arg_count(cmd, debug_ARG))
@@ -903,10 +905,34 @@ static int _get_settings(struct cmd_context *cmd)
 	}
 
 	cmd->partial_activation = 0;
+	cmd->degraded_activation = 0;
+	activation_mode = find_config_tree_str(cmd, activation_mode_CFG, NULL);
+	if (!activation_mode)
+		activation_mode = DEFAULT_ACTIVATION_MODE;
+
+	if (arg_count(cmd, activationmode_ARG)) {
+		activation_mode = arg_str_value(cmd, activationmode_ARG,
+						activation_mode);
+
+		/* complain only if the two arguments conflict */
+		if (arg_count(cmd, partial_ARG) &&
+		    strcmp(activation_mode, "partial")) {
+			log_error("--partial and --activationmode are mutually"
+				  " exclusive arguments");
+			return EINVALID_CMD_LINE;
+		}
+	} else if (arg_count(cmd, partial_ARG))
+		activation_mode = "partial";
 
-	if (arg_count(cmd, partial_ARG)) {
+	if (!strcmp(activation_mode, "partial")) {
 		cmd->partial_activation = 1;
 		log_warn("PARTIAL MODE. Incomplete logical volumes will be processed.");
+	} else if (!strcmp(activation_mode, "degraded")) {
+		cmd->degraded_activation = 1;
+		log_debug("DEGRADED MODE. Incomplete RAID LVs will be processed.");
+	} else if (strcmp(activation_mode, "complete")) {
+		log_error("Invalid activation mode given.");
+		return EINVALID_CMD_LINE;
 	}
 
 	if (arg_count(cmd, ignorelockingfailure_ARG) || arg_count(cmd, sysinit_ARG))