o First changes to add snapshot support.

I'm taking a different route from LVM1 here in that snapshots are a
seperate entity from the logical volumes, I think of them as an
application of an LV (or two lvs rather).  As such there is a list of
snapshots held against the vg, and there is *not* a SNAPSHOT, or
SHAPSHOT_ORG flag in lv->status.

lib/Makefile.in

@@ -40,13 +40,14 @@ SOURCES=\
 	format_text/import.c \
 	label/label.c \
 	label/uuid-map.c \
-	locking/locking.c \
 	locking/file_locking.c \
+	locking/locking.c \
 	log/log.c \
 	metadata/lv_manip.c \
 	metadata/merge.c \
 	metadata/metadata.c \
 	metadata/pv_map.c \
+	metadata/snapshot_manip.c \
 	misc/lvm-file.c \
 	mm/dbg_malloc.c \
 	mm/pool.c \

lib/metadata/metadata.h

@@ -94,6 +94,10 @@ struct volume_group {
         /* logical volumes */
         uint32_t lv_count;
 	struct list lvs;
+
+	/* snapshots */
+	uint32_t snapshot_count;
+	struct list snapshots;
 };
 
 struct stripe_segment {
@@ -128,6 +132,14 @@ struct logical_volume {
 	struct list segments;
 };
 
+struct snapshot {
+	int persistent;		/* boolean */
+	uint32_t chunk_size;	/* in 512 byte sectors */
+
+	struct logical_volume *origin;
+	struct logical_volume *cow;
+};
+
 struct name_list {
 	struct list list;
 	char *name;
@@ -143,6 +155,12 @@ struct lv_list {
 	struct logical_volume *lv;
 };
 
+struct snapshot_list {
+	struct list list;
+
+	struct snapshot *snapshot;
+};
+
 struct format_instance {
 	struct cmd_context *cmd;
 	struct format_handler *ops;
@@ -315,4 +333,19 @@ int lv_check_segments(struct logical_volume *lv);
 int lv_merge_segments(struct logical_volume *lv);
 
 
+/*
+ * Useful functions for managing snapshots.
+ */
+int lv_is_origin(struct volume_group *vg, struct logical_volume *lv);
+int lv_is_cow(struct volume_group *vg, struct logical_volume *lv);
+
+int vg_add_snapshot(struct volume_group *vg,
+		    struct logical_volume *origin,
+		    struct logical_volume *cow,
+		    int persistent,
+		    uint32_t chunk_size);
+
+int vg_remove_snapshot(struct volume_group *vg, struct logical_volume *cow);
+
+
 #endif

lib/metadata/snapshot_manip.c

@@ -0,0 +1,96 @@
+/*
+ * Copyright (C) 2002 Sistina Software (UK) Limited.
+ *
+ * This file is released under the LGPL.
+ */
+
+#include "log.h"
+#include "metadata.h"
+#include "toolcontext.h"
+
+int lv_is_origin(struct volume_group *vg, struct logical_volume *lv)
+{
+	struct list *slh;
+	struct snapshot *s;
+
+	list_iterate (slh, &vg->snapshots) {
+		s = list_item(slh, struct snapshot_list)->snapshot;
+		if (s->origin == lv)
+			return 1;
+	}
+
+	return 0;
+}
+
+int lv_is_cow(struct volume_group *vg, struct logical_volume *lv)
+{
+	struct list *slh;
+	struct snapshot *s;
+
+	list_iterate (slh, &vg->snapshots) {
+		s = list_item(slh, struct snapshot_list)->snapshot;
+		if (s->cow == lv)
+			return 1;
+	}
+
+	return 0;
+}
+
+int vg_add_snapshot(struct volume_group *vg,
+		    struct logical_volume *origin,
+		    struct logical_volume *cow,
+		    int persistent,
+		    uint32_t chunk_size)
+{
+	struct snapshot *s;
+	struct snapshot_list *sl;
+	struct pool *mem = vg->cmd->mem;
+
+	/*
+	 * Is the cow device already being used ?
+	 */
+	if (lv_is_cow(vg, cow)) {
+		log_err("'%s' is already in use as a snapshot.", cow->name);
+		return 0;
+	}
+
+	if (!(s = pool_alloc(mem, sizeof(*s)))) {
+		stack;
+		return 0;
+	}
+
+	s->persistent = persistent;
+	s->chunk_size = chunk_size;
+	s->origin = origin;
+	s->cow = cow;
+
+	if (!(sl = pool_alloc(mem, sizeof(*sl)))) {
+		stack;
+		pool_free(mem, s);
+		return 0;
+	}
+
+	sl->snapshot = s;
+	list_add(&vg->snapshots, &sl->list);
+
+	return 1;
+}
+
+int vg_remove_snapshot(struct volume_group *vg, struct logical_volume *cow)
+{
+	struct list *slh;
+	struct snapshot_list *sl;
+
+	list_iterate (slh, &vg->snapshots) {
+		sl = list_item(slh, struct snapshot_list);
+
+		if (sl->snapshot->cow == cow) {
+			list_del(slh);
+			return 1;
+		}
+	}
+
+	/* fail */
+	log_err("Asked to remove an unknow snapshot.");
+	return 0;
+}