dm table: add always writeable feature

Add a target feature flag DM_TARGET_ALWAYS_WRITEABLE to indicate that a target
does not support read-only mode.

The initial implementation of the thin provisioning target uses this.

Signed-off-by: Alasdair G Kergon <agk@redhat.com>

1 files changed, 7 insertions, 0 deletions

diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 294e78a7fccd..cc58e2d7c032 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -166,6 +166,13 @@ struct target_type {
 #define DM_TARGET_SINGLETON             0x00000001
 #define dm_target_needs_singleton(type) ((type)->features & DM_TARGET_SINGLETON)
 
+/*
+ * Indicates that a target does not support read-only devices.
+ */
+#define DM_TARGET_ALWAYS_WRITEABLE      0x00000002
+#define dm_target_always_writeable(type) \
+                ((type)->features & DM_TARGET_ALWAYS_WRITEABLE)
+
 struct dm_target {
         struct dm_table *table;
         struct target_type *type;