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>
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index 2ec3482..9917141 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -774,6 +774,12 @@
t->singleton = 1;
}
+ if (dm_target_always_writeable(tgt->type) && !(t->mode & FMODE_WRITE)) {
+ DMERR("%s: target type %s may not be included in read-only tables",
+ dm_device_name(t->md), type);
+ return -EINVAL;
+ }
+
tgt->table = t;
tgt->begin = start;
tgt->len = len;
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 294e78a..cc58e2d 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -166,6 +166,13 @@
#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;