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 (file)
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -774,6 +774,12 @@ int dm_table_add_target(struct dm_table *t, const char *type,
                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 (file)
--- 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;