dm ioctl: retrieve status from inactive table

Add the flag DM_QUERY_INACTIVE_TABLE_FLAG to the ioctls to return
infomation about the loaded-but-not-yet-active table instead of the live
table.  Prior to this patch it was impossible to obtain this information
until the device had been 'resumed'.

Userspace dmsetup and libdevmapper support the flag as of version 1.02.40.
e.g. dmsetup info --inactive vg1-lv1

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

1 files changed, 57 insertions, 13 deletions

diff --git a/drivers/md/dm-ioctl.c b/drivers/md/dm-ioctl.c
index d06dd39856f3..a3d20265ffc1 100644
--- a/drivers/md/dm-ioctl.c
+++ b/drivers/md/dm-ioctl.c
@@ -523,8 +523,6 @@ static int list_versions(struct dm_ioctl *param, size_t param_size)
 	return 0;
 }
 
-
-
 static int check_name(const char *name)
 {
 	if (strchr(name, '/')) {
@@ -536,6 +534,40 @@ static int check_name(const char *name)
 }
 
 /*
+ * On successful return, the caller must not attempt to acquire
+ * _hash_lock without first calling dm_table_put, because dm_table_destroy
+ * waits for this dm_table_put and could be called under this lock.
+ */
+static struct dm_table *dm_get_inactive_table(struct mapped_device *md)
+{
+	struct hash_cell *hc;
+	struct dm_table *table = NULL;
+
+	down_read(&_hash_lock);
+	hc = dm_get_mdptr(md);
+	if (!hc || hc->md != md) {
+		DMWARN("device has been removed from the dev hash table.");
+		goto out;
+	}
+
+	table = hc->new_map;
+	if (table)
+		dm_table_get(table);
+
+out:
+	up_read(&_hash_lock);
+
+	return table;
+}
+
+static struct dm_table *dm_get_live_or_inactive_table(struct mapped_device *md,
+						      struct dm_ioctl *param)
+{
+	return (param->flags & DM_QUERY_INACTIVE_TABLE_FLAG) ?
+		dm_get_inactive_table(md) : dm_get_live_table(md);
+}
+
+/*
  * Fills in a dm_ioctl structure, ready for sending back to
  * userland.
  */
@@ -559,18 +591,30 @@ static int __dev_status(struct mapped_device *md, struct dm_ioctl *param)
 	 */
 	param->open_count = dm_open_count(md);
 
-	if (get_disk_ro(disk))
-		param->flags |= DM_READONLY_FLAG;
-
 	param->event_nr = dm_get_event_nr(md);
+	param->target_count = 0;
 
 	table = dm_get_live_table(md);
 	if (table) {
-		param->flags |= DM_ACTIVE_PRESENT_FLAG;
-		param->target_count = dm_table_get_num_targets(table);
+		if (!(param->flags & DM_QUERY_INACTIVE_TABLE_FLAG)) {
+			if (get_disk_ro(disk))
+				param->flags |= DM_READONLY_FLAG;
+			param->target_count = dm_table_get_num_targets(table);
+		}
 		dm_table_put(table);
-	} else
-		param->target_count = 0;
+
+		param->flags |= DM_ACTIVE_PRESENT_FLAG;
+	}
+
+	if (param->flags & DM_QUERY_INACTIVE_TABLE_FLAG) {
+		table = dm_get_inactive_table(md);
+		if (table) {
+			if (!(dm_table_get_mode(table) & FMODE_WRITE))
+				param->flags |= DM_READONLY_FLAG;
+			param->target_count = dm_table_get_num_targets(table);
+			dm_table_put(table);
+		}
+	}
 
 	return 0;
 }
@@ -993,7 +1037,7 @@ static int dev_wait(struct dm_ioctl *param, size_t param_size)
 	if (r)
 		goto out;
 
-	table = dm_get_live_table(md);
+	table = dm_get_live_or_inactive_table(md, param);
 	if (table) {
 		retrieve_status(table, param, param_size);
 		dm_table_put(table);
@@ -1226,7 +1270,7 @@ static int table_deps(struct dm_ioctl *param, size_t param_size)
 	if (r)
 		goto out;
 
-	table = dm_get_live_table(md);
+	table = dm_get_live_or_inactive_table(md, param);
 	if (table) {
 		retrieve_deps(table, param, param_size);
 		dm_table_put(table);
@@ -1255,13 +1299,13 @@ static int table_status(struct dm_ioctl *param, size_t param_size)
 	if (r)
 		goto out;
 
-	table = dm_get_live_table(md);
+	table = dm_get_live_or_inactive_table(md, param);
 	if (table) {
 		retrieve_status(table, param, param_size);
 		dm_table_put(table);
 	}
 
- out:
+out:
 	dm_put(md);
 	return r;
 }