FreeBSD/Linux Kernel Cross Reference
sys/contrib/openzfs/module/zfs/space_reftree.c

     /*
      * 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 https://opensource.org/licenses/CDDL-1.0.
     * 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 2009 Sun Microsystems, Inc.  All rights reserved.
     * Use is subject to license terms.
     */
    /*
     * Copyright (c) 2013, 2019 by Delphix. All rights reserved.
     */
    
    #include <sys/zfs_context.h>
    #include <sys/range_tree.h>
    #include <sys/space_reftree.h>
    
    /*
     * Space reference trees.
     *
     * A range tree is a collection of integers.  Every integer is either
     * in the tree, or it's not.  A space reference tree generalizes
     * the idea: it allows its members to have arbitrary reference counts,
     * as opposed to the implicit reference count of 0 or 1 in a range tree.
     * This representation comes in handy when computing the union or
     * intersection of multiple space maps.  For example, the union of
     * N range trees is the subset of the reference tree with refcnt >= 1.
     * The intersection of N range trees is the subset with refcnt >= N.
     *
     * [It's very much like a Fourier transform.  Unions and intersections
     * are hard to perform in the 'range tree domain', so we convert the trees
     * into the 'reference count domain', where it's trivial, then invert.]
     *
     * vdev_dtl_reassess() uses computations of this form to determine
     * DTL_MISSING and DTL_OUTAGE for interior vdevs -- e.g. a RAID-Z vdev
     * has an outage wherever refcnt >= vdev_nparity + 1, and a mirror vdev
     * has an outage wherever refcnt >= vdev_children.
     */
    static int
    space_reftree_compare(const void *x1, const void *x2)
    {
            const space_ref_t *sr1 = (const space_ref_t *)x1;
            const space_ref_t *sr2 = (const space_ref_t *)x2;
    
            int cmp = TREE_CMP(sr1->sr_offset, sr2->sr_offset);
            if (likely(cmp))
                    return (cmp);
    
            return (TREE_PCMP(sr1, sr2));
    }
    
    void
    space_reftree_create(avl_tree_t *t)
    {
            avl_create(t, space_reftree_compare,
                sizeof (space_ref_t), offsetof(space_ref_t, sr_node));
    }
    
    void
    space_reftree_destroy(avl_tree_t *t)
    {
            space_ref_t *sr;
            void *cookie = NULL;
    
            while ((sr = avl_destroy_nodes(t, &cookie)) != NULL)
                    kmem_free(sr, sizeof (*sr));
    
            avl_destroy(t);
    }
    
    static void
    space_reftree_add_node(avl_tree_t *t, uint64_t offset, int64_t refcnt)
    {
            space_ref_t *sr;
    
            sr = kmem_alloc(sizeof (*sr), KM_SLEEP);
            sr->sr_offset = offset;
            sr->sr_refcnt = refcnt;
    
            avl_add(t, sr);
    }
    
    void
    space_reftree_add_seg(avl_tree_t *t, uint64_t start, uint64_t end,
       int64_t refcnt)
   {
           space_reftree_add_node(t, start, refcnt);
           space_reftree_add_node(t, end, -refcnt);
   }
   
   /*
    * Convert (or add) a range tree into a reference tree.
    */
   void
   space_reftree_add_map(avl_tree_t *t, range_tree_t *rt, int64_t refcnt)
   {
           zfs_btree_index_t where;
   
           for (range_seg_t *rs = zfs_btree_first(&rt->rt_root, &where); rs; rs =
               zfs_btree_next(&rt->rt_root, &where, &where)) {
                   space_reftree_add_seg(t, rs_get_start(rs, rt), rs_get_end(rs,
                       rt),  refcnt);
           }
   }
   
   /*
    * Convert a reference tree into a range tree.  The range tree will contain
    * all members of the reference tree for which refcnt >= minref.
    */
   void
   space_reftree_generate_map(avl_tree_t *t, range_tree_t *rt, int64_t minref)
   {
           uint64_t start = -1ULL;
           int64_t refcnt = 0;
           space_ref_t *sr;
   
           range_tree_vacate(rt, NULL, NULL);
   
           for (sr = avl_first(t); sr != NULL; sr = AVL_NEXT(t, sr)) {
                   refcnt += sr->sr_refcnt;
                   if (refcnt >= minref) {
                           if (start == -1ULL) {
                                   start = sr->sr_offset;
                           }
                   } else {
                           if (start != -1ULL) {
                                   uint64_t end = sr->sr_offset;
                                   ASSERT(start <= end);
                                   if (end > start)
                                           range_tree_add(rt, start, end - start);
                                   start = -1ULL;
                           }
                   }
           }
           ASSERT(refcnt == 0);
           ASSERT(start == -1ULL);
   }

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