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-rw-r--r--lib/libzfs/libzfs_graph.c662
1 files changed, 662 insertions, 0 deletions
diff --git a/lib/libzfs/libzfs_graph.c b/lib/libzfs/libzfs_graph.c
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+++ b/lib/libzfs/libzfs_graph.c
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+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
+ * or http://www.opensolaris.org/os/licensing.
+ * See the License for the specific language governing permissions
+ * and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+/*
+ * Copyright 2008 Sun Microsystems, Inc. All rights reserved.
+ * Use is subject to license terms.
+ */
+
+#pragma ident "%Z%%M% %I% %E% SMI"
+
+/*
+ * Iterate over all children of the current object. This includes the normal
+ * dataset hierarchy, but also arbitrary hierarchies due to clones. We want to
+ * walk all datasets in the pool, and construct a directed graph of the form:
+ *
+ * home
+ * |
+ * +----+----+
+ * | |
+ * v v ws
+ * bar baz |
+ * | |
+ * v v
+ * @yesterday ----> foo
+ *
+ * In order to construct this graph, we have to walk every dataset in the pool,
+ * because the clone parent is stored as a property of the child, not the
+ * parent. The parent only keeps track of the number of clones.
+ *
+ * In the normal case (without clones) this would be rather expensive. To avoid
+ * unnecessary computation, we first try a walk of the subtree hierarchy
+ * starting from the initial node. At each dataset, we construct a node in the
+ * graph and an edge leading from its parent. If we don't see any snapshots
+ * with a non-zero clone count, then we are finished.
+ *
+ * If we do find a cloned snapshot, then we finish the walk of the current
+ * subtree, but indicate that we need to do a complete walk. We then perform a
+ * global walk of all datasets, avoiding the subtree we already processed.
+ *
+ * At the end of this, we'll end up with a directed graph of all relevant (and
+ * possible some irrelevant) datasets in the system. We need to both find our
+ * limiting subgraph and determine a safe ordering in which to destroy the
+ * datasets. We do a topological ordering of our graph starting at our target
+ * dataset, and then walk the results in reverse.
+ *
+ * It's possible for the graph to have cycles if, for example, the user renames
+ * a clone to be the parent of its origin snapshot. The user can request to
+ * generate an error in this case, or ignore the cycle and continue.
+ *
+ * When removing datasets, we want to destroy the snapshots in chronological
+ * order (because this is the most efficient method). In order to accomplish
+ * this, we store the creation transaction group with each vertex and keep each
+ * vertex's edges sorted according to this value. The topological sort will
+ * automatically walk the snapshots in the correct order.
+ */
+
+#include <assert.h>
+#include <libintl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <strings.h>
+#include <unistd.h>
+
+#include <libzfs.h>
+
+#include "libzfs_impl.h"
+#include "zfs_namecheck.h"
+
+#define MIN_EDGECOUNT 4
+
+/*
+ * Vertex structure. Indexed by dataset name, this structure maintains a list
+ * of edges to other vertices.
+ */
+struct zfs_edge;
+typedef struct zfs_vertex {
+ char zv_dataset[ZFS_MAXNAMELEN];
+ struct zfs_vertex *zv_next;
+ int zv_visited;
+ uint64_t zv_txg;
+ struct zfs_edge **zv_edges;
+ int zv_edgecount;
+ int zv_edgealloc;
+} zfs_vertex_t;
+
+enum {
+ VISIT_SEEN = 1,
+ VISIT_SORT_PRE,
+ VISIT_SORT_POST
+};
+
+/*
+ * Edge structure. Simply maintains a pointer to the destination vertex. There
+ * is no need to store the source vertex, since we only use edges in the context
+ * of the source vertex.
+ */
+typedef struct zfs_edge {
+ zfs_vertex_t *ze_dest;
+ struct zfs_edge *ze_next;
+} zfs_edge_t;
+
+#define ZFS_GRAPH_SIZE 1027 /* this could be dynamic some day */
+
+/*
+ * Graph structure. Vertices are maintained in a hash indexed by dataset name.
+ */
+typedef struct zfs_graph {
+ zfs_vertex_t **zg_hash;
+ size_t zg_size;
+ size_t zg_nvertex;
+ const char *zg_root;
+ int zg_clone_count;
+} zfs_graph_t;
+
+/*
+ * Allocate a new edge pointing to the target vertex.
+ */
+static zfs_edge_t *
+zfs_edge_create(libzfs_handle_t *hdl, zfs_vertex_t *dest)
+{
+ zfs_edge_t *zep = zfs_alloc(hdl, sizeof (zfs_edge_t));
+
+ if (zep == NULL)
+ return (NULL);
+
+ zep->ze_dest = dest;
+
+ return (zep);
+}
+
+/*
+ * Destroy an edge.
+ */
+static void
+zfs_edge_destroy(zfs_edge_t *zep)
+{
+ free(zep);
+}
+
+/*
+ * Allocate a new vertex with the given name.
+ */
+static zfs_vertex_t *
+zfs_vertex_create(libzfs_handle_t *hdl, const char *dataset)
+{
+ zfs_vertex_t *zvp = zfs_alloc(hdl, sizeof (zfs_vertex_t));
+
+ if (zvp == NULL)
+ return (NULL);
+
+ assert(strlen(dataset) < ZFS_MAXNAMELEN);
+
+ (void) strlcpy(zvp->zv_dataset, dataset, sizeof (zvp->zv_dataset));
+
+ if ((zvp->zv_edges = zfs_alloc(hdl,
+ MIN_EDGECOUNT * sizeof (void *))) == NULL) {
+ free(zvp);
+ return (NULL);
+ }
+
+ zvp->zv_edgealloc = MIN_EDGECOUNT;
+
+ return (zvp);
+}
+
+/*
+ * Destroy a vertex. Frees up any associated edges.
+ */
+static void
+zfs_vertex_destroy(zfs_vertex_t *zvp)
+{
+ int i;
+
+ for (i = 0; i < zvp->zv_edgecount; i++)
+ zfs_edge_destroy(zvp->zv_edges[i]);
+
+ free(zvp->zv_edges);
+ free(zvp);
+}
+
+/*
+ * Given a vertex, add an edge to the destination vertex.
+ */
+static int
+zfs_vertex_add_edge(libzfs_handle_t *hdl, zfs_vertex_t *zvp,
+ zfs_vertex_t *dest)
+{
+ zfs_edge_t *zep = zfs_edge_create(hdl, dest);
+
+ if (zep == NULL)
+ return (-1);
+
+ if (zvp->zv_edgecount == zvp->zv_edgealloc) {
+ void *ptr;
+
+ if ((ptr = zfs_realloc(hdl, zvp->zv_edges,
+ zvp->zv_edgealloc * sizeof (void *),
+ zvp->zv_edgealloc * 2 * sizeof (void *))) == NULL)
+ return (-1);
+
+ zvp->zv_edges = ptr;
+ zvp->zv_edgealloc *= 2;
+ }
+
+ zvp->zv_edges[zvp->zv_edgecount++] = zep;
+
+ return (0);
+}
+
+static int
+zfs_edge_compare(const void *a, const void *b)
+{
+ const zfs_edge_t *ea = *((zfs_edge_t **)a);
+ const zfs_edge_t *eb = *((zfs_edge_t **)b);
+
+ if (ea->ze_dest->zv_txg < eb->ze_dest->zv_txg)
+ return (-1);
+ if (ea->ze_dest->zv_txg > eb->ze_dest->zv_txg)
+ return (1);
+ return (0);
+}
+
+/*
+ * Sort the given vertex edges according to the creation txg of each vertex.
+ */
+static void
+zfs_vertex_sort_edges(zfs_vertex_t *zvp)
+{
+ if (zvp->zv_edgecount == 0)
+ return;
+
+ qsort(zvp->zv_edges, zvp->zv_edgecount, sizeof (void *),
+ zfs_edge_compare);
+}
+
+/*
+ * Construct a new graph object. We allow the size to be specified as a
+ * parameter so in the future we can size the hash according to the number of
+ * datasets in the pool.
+ */
+static zfs_graph_t *
+zfs_graph_create(libzfs_handle_t *hdl, const char *dataset, size_t size)
+{
+ zfs_graph_t *zgp = zfs_alloc(hdl, sizeof (zfs_graph_t));
+
+ if (zgp == NULL)
+ return (NULL);
+
+ zgp->zg_size = size;
+ if ((zgp->zg_hash = zfs_alloc(hdl,
+ size * sizeof (zfs_vertex_t *))) == NULL) {
+ free(zgp);
+ return (NULL);
+ }
+
+ zgp->zg_root = dataset;
+ zgp->zg_clone_count = 0;
+
+ return (zgp);
+}
+
+/*
+ * Destroy a graph object. We have to iterate over all the hash chains,
+ * destroying each vertex in the process.
+ */
+static void
+zfs_graph_destroy(zfs_graph_t *zgp)
+{
+ int i;
+ zfs_vertex_t *current, *next;
+
+ for (i = 0; i < zgp->zg_size; i++) {
+ current = zgp->zg_hash[i];
+ while (current != NULL) {
+ next = current->zv_next;
+ zfs_vertex_destroy(current);
+ current = next;
+ }
+ }
+
+ free(zgp->zg_hash);
+ free(zgp);
+}
+
+/*
+ * Graph hash function. Classic bernstein k=33 hash function, taken from
+ * usr/src/cmd/sgs/tools/common/strhash.c
+ */
+static size_t
+zfs_graph_hash(zfs_graph_t *zgp, const char *str)
+{
+ size_t hash = 5381;
+ int c;
+
+ while ((c = *str++) != 0)
+ hash = ((hash << 5) + hash) + c; /* hash * 33 + c */
+
+ return (hash % zgp->zg_size);
+}
+
+/*
+ * Given a dataset name, finds the associated vertex, creating it if necessary.
+ */
+static zfs_vertex_t *
+zfs_graph_lookup(libzfs_handle_t *hdl, zfs_graph_t *zgp, const char *dataset,
+ uint64_t txg)
+{
+ size_t idx = zfs_graph_hash(zgp, dataset);
+ zfs_vertex_t *zvp;
+
+ for (zvp = zgp->zg_hash[idx]; zvp != NULL; zvp = zvp->zv_next) {
+ if (strcmp(zvp->zv_dataset, dataset) == 0) {
+ if (zvp->zv_txg == 0)
+ zvp->zv_txg = txg;
+ return (zvp);
+ }
+ }
+
+ if ((zvp = zfs_vertex_create(hdl, dataset)) == NULL)
+ return (NULL);
+
+ zvp->zv_next = zgp->zg_hash[idx];
+ zvp->zv_txg = txg;
+ zgp->zg_hash[idx] = zvp;
+ zgp->zg_nvertex++;
+
+ return (zvp);
+}
+
+/*
+ * Given two dataset names, create an edge between them. For the source vertex,
+ * mark 'zv_visited' to indicate that we have seen this vertex, and not simply
+ * created it as a destination of another edge. If 'dest' is NULL, then this
+ * is an individual vertex (i.e. the starting vertex), so don't add an edge.
+ */
+static int
+zfs_graph_add(libzfs_handle_t *hdl, zfs_graph_t *zgp, const char *source,
+ const char *dest, uint64_t txg)
+{
+ zfs_vertex_t *svp, *dvp;
+
+ if ((svp = zfs_graph_lookup(hdl, zgp, source, 0)) == NULL)
+ return (-1);
+ svp->zv_visited = VISIT_SEEN;
+ if (dest != NULL) {
+ dvp = zfs_graph_lookup(hdl, zgp, dest, txg);
+ if (dvp == NULL)
+ return (-1);
+ if (zfs_vertex_add_edge(hdl, svp, dvp) != 0)
+ return (-1);
+ }
+
+ return (0);
+}
+
+/*
+ * Iterate over all children of the given dataset, adding any vertices
+ * as necessary. Returns -1 if there was an error, or 0 otherwise.
+ * This is a simple recursive algorithm - the ZFS namespace typically
+ * is very flat. We manually invoke the necessary ioctl() calls to
+ * avoid the overhead and additional semantics of zfs_open().
+ */
+static int
+iterate_children(libzfs_handle_t *hdl, zfs_graph_t *zgp, const char *dataset)
+{
+ zfs_cmd_t zc = { 0 };
+ zfs_vertex_t *zvp;
+
+ /*
+ * Look up the source vertex, and avoid it if we've seen it before.
+ */
+ zvp = zfs_graph_lookup(hdl, zgp, dataset, 0);
+ if (zvp == NULL)
+ return (-1);
+ if (zvp->zv_visited == VISIT_SEEN)
+ return (0);
+
+ /*
+ * Iterate over all children
+ */
+ for ((void) strlcpy(zc.zc_name, dataset, sizeof (zc.zc_name));
+ ioctl(hdl->libzfs_fd, ZFS_IOC_DATASET_LIST_NEXT, &zc) == 0;
+ (void) strlcpy(zc.zc_name, dataset, sizeof (zc.zc_name))) {
+
+ /*
+ * Ignore private dataset names.
+ */
+ if (dataset_name_hidden(zc.zc_name))
+ continue;
+
+ /*
+ * Get statistics for this dataset, to determine the type of the
+ * dataset and clone statistics. If this fails, the dataset has
+ * since been removed, and we're pretty much screwed anyway.
+ */
+ zc.zc_objset_stats.dds_origin[0] = '\0';
+ if (ioctl(hdl->libzfs_fd, ZFS_IOC_OBJSET_STATS, &zc) != 0)
+ continue;
+
+ if (zc.zc_objset_stats.dds_origin[0] != '\0') {
+ if (zfs_graph_add(hdl, zgp,
+ zc.zc_objset_stats.dds_origin, zc.zc_name,
+ zc.zc_objset_stats.dds_creation_txg) != 0)
+ return (-1);
+ /*
+ * Count origins only if they are contained in the graph
+ */
+ if (isa_child_of(zc.zc_objset_stats.dds_origin,
+ zgp->zg_root))
+ zgp->zg_clone_count--;
+ }
+
+ /*
+ * Add an edge between the parent and the child.
+ */
+ if (zfs_graph_add(hdl, zgp, dataset, zc.zc_name,
+ zc.zc_objset_stats.dds_creation_txg) != 0)
+ return (-1);
+
+ /*
+ * Recursively visit child
+ */
+ if (iterate_children(hdl, zgp, zc.zc_name))
+ return (-1);
+ }
+
+ /*
+ * Now iterate over all snapshots.
+ */
+ bzero(&zc, sizeof (zc));
+
+ for ((void) strlcpy(zc.zc_name, dataset, sizeof (zc.zc_name));
+ ioctl(hdl->libzfs_fd, ZFS_IOC_SNAPSHOT_LIST_NEXT, &zc) == 0;
+ (void) strlcpy(zc.zc_name, dataset, sizeof (zc.zc_name))) {
+
+ /*
+ * Get statistics for this dataset, to determine the type of the
+ * dataset and clone statistics. If this fails, the dataset has
+ * since been removed, and we're pretty much screwed anyway.
+ */
+ if (ioctl(hdl->libzfs_fd, ZFS_IOC_OBJSET_STATS, &zc) != 0)
+ continue;
+
+ /*
+ * Add an edge between the parent and the child.
+ */
+ if (zfs_graph_add(hdl, zgp, dataset, zc.zc_name,
+ zc.zc_objset_stats.dds_creation_txg) != 0)
+ return (-1);
+
+ zgp->zg_clone_count += zc.zc_objset_stats.dds_num_clones;
+ }
+
+ zvp->zv_visited = VISIT_SEEN;
+
+ return (0);
+}
+
+/*
+ * Returns false if there are no snapshots with dependent clones in this
+ * subtree or if all of those clones are also in this subtree. Returns
+ * true if there is an error or there are external dependents.
+ */
+static boolean_t
+external_dependents(libzfs_handle_t *hdl, zfs_graph_t *zgp, const char *dataset)
+{
+ zfs_cmd_t zc = { 0 };
+
+ /*
+ * Check whether this dataset is a clone or has clones since
+ * iterate_children() only checks the children.
+ */
+ (void) strlcpy(zc.zc_name, dataset, sizeof (zc.zc_name));
+ if (ioctl(hdl->libzfs_fd, ZFS_IOC_OBJSET_STATS, &zc) != 0)
+ return (B_TRUE);
+
+ if (zc.zc_objset_stats.dds_origin[0] != '\0') {
+ if (zfs_graph_add(hdl, zgp,
+ zc.zc_objset_stats.dds_origin, zc.zc_name,
+ zc.zc_objset_stats.dds_creation_txg) != 0)
+ return (B_TRUE);
+ if (isa_child_of(zc.zc_objset_stats.dds_origin, dataset))
+ zgp->zg_clone_count--;
+ }
+
+ if ((zc.zc_objset_stats.dds_num_clones) ||
+ iterate_children(hdl, zgp, dataset))
+ return (B_TRUE);
+
+ return (zgp->zg_clone_count != 0);
+}
+
+/*
+ * Construct a complete graph of all necessary vertices. First, iterate over
+ * only our object's children. If no cloned snapshots are found, or all of
+ * the cloned snapshots are in this subtree then return a graph of the subtree.
+ * Otherwise, start at the root of the pool and iterate over all datasets.
+ */
+static zfs_graph_t *
+construct_graph(libzfs_handle_t *hdl, const char *dataset)
+{
+ zfs_graph_t *zgp = zfs_graph_create(hdl, dataset, ZFS_GRAPH_SIZE);
+ int ret = 0;
+
+ if (zgp == NULL)
+ return (zgp);
+
+ if ((strchr(dataset, '/') == NULL) ||
+ (external_dependents(hdl, zgp, dataset))) {
+ /*
+ * Determine pool name and try again.
+ */
+ int len = strcspn(dataset, "/@") + 1;
+ char *pool = zfs_alloc(hdl, len);
+
+ if (pool == NULL) {
+ zfs_graph_destroy(zgp);
+ return (NULL);
+ }
+ (void) strlcpy(pool, dataset, len);
+
+ if (iterate_children(hdl, zgp, pool) == -1 ||
+ zfs_graph_add(hdl, zgp, pool, NULL, 0) != 0) {
+ free(pool);
+ zfs_graph_destroy(zgp);
+ return (NULL);
+ }
+ free(pool);
+ }
+
+ if (ret == -1 || zfs_graph_add(hdl, zgp, dataset, NULL, 0) != 0) {
+ zfs_graph_destroy(zgp);
+ return (NULL);
+ }
+
+ return (zgp);
+}
+
+/*
+ * Given a graph, do a recursive topological sort into the given array. This is
+ * really just a depth first search, so that the deepest nodes appear first.
+ * hijack the 'zv_visited' marker to avoid visiting the same vertex twice.
+ */
+static int
+topo_sort(libzfs_handle_t *hdl, boolean_t allowrecursion, char **result,
+ size_t *idx, zfs_vertex_t *zgv)
+{
+ int i;
+
+ if (zgv->zv_visited == VISIT_SORT_PRE && !allowrecursion) {
+ /*
+ * If we've already seen this vertex as part of our depth-first
+ * search, then we have a cyclic dependency, and we must return
+ * an error.
+ */
+ zfs_error_aux(hdl, dgettext(TEXT_DOMAIN,
+ "recursive dependency at '%s'"),
+ zgv->zv_dataset);
+ return (zfs_error(hdl, EZFS_RECURSIVE,
+ dgettext(TEXT_DOMAIN,
+ "cannot determine dependent datasets")));
+ } else if (zgv->zv_visited >= VISIT_SORT_PRE) {
+ /*
+ * If we've already processed this as part of the topological
+ * sort, then don't bother doing so again.
+ */
+ return (0);
+ }
+
+ zgv->zv_visited = VISIT_SORT_PRE;
+
+ /* avoid doing a search if we don't have to */
+ zfs_vertex_sort_edges(zgv);
+ for (i = 0; i < zgv->zv_edgecount; i++) {
+ if (topo_sort(hdl, allowrecursion, result, idx,
+ zgv->zv_edges[i]->ze_dest) != 0)
+ return (-1);
+ }
+
+ /* we may have visited this in the course of the above */
+ if (zgv->zv_visited == VISIT_SORT_POST)
+ return (0);
+
+ if ((result[*idx] = zfs_alloc(hdl,
+ strlen(zgv->zv_dataset) + 1)) == NULL)
+ return (-1);
+
+ (void) strcpy(result[*idx], zgv->zv_dataset);
+ *idx += 1;
+ zgv->zv_visited = VISIT_SORT_POST;
+ return (0);
+}
+
+/*
+ * The only public interface for this file. Do the dirty work of constructing a
+ * child list for the given object. Construct the graph, do the toplogical
+ * sort, and then return the array of strings to the caller.
+ *
+ * The 'allowrecursion' parameter controls behavior when cycles are found. If
+ * it is set, the the cycle is ignored and the results returned as if the cycle
+ * did not exist. If it is not set, then the routine will generate an error if
+ * a cycle is found.
+ */
+int
+get_dependents(libzfs_handle_t *hdl, boolean_t allowrecursion,
+ const char *dataset, char ***result, size_t *count)
+{
+ zfs_graph_t *zgp;
+ zfs_vertex_t *zvp;
+
+ if ((zgp = construct_graph(hdl, dataset)) == NULL)
+ return (-1);
+
+ if ((*result = zfs_alloc(hdl,
+ zgp->zg_nvertex * sizeof (char *))) == NULL) {
+ zfs_graph_destroy(zgp);
+ return (-1);
+ }
+
+ if ((zvp = zfs_graph_lookup(hdl, zgp, dataset, 0)) == NULL) {
+ free(*result);
+ zfs_graph_destroy(zgp);
+ return (-1);
+ }
+
+ *count = 0;
+ if (topo_sort(hdl, allowrecursion, *result, count, zvp) != 0) {
+ free(*result);
+ zfs_graph_destroy(zgp);
+ return (-1);
+ }
+
+ /*
+ * Get rid of the last entry, which is our starting vertex and not
+ * strictly a dependent.
+ */
+ assert(*count > 0);
+ free((*result)[*count - 1]);
+ (*count)--;
+
+ zfs_graph_destroy(zgp);
+
+ return (0);
+}
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