subversion/libsvn_fs_fs/fs.h

/* fs.h : interface to Subversion filesystem, private to libsvn_fs
 *
 * ====================================================================
 *    Licensed to the Apache Software Foundation (ASF) under one
 *    or more contributor license agreements.  See the NOTICE file
 *    distributed with this work for additional information
 *    regarding copyright ownership.  The ASF licenses this file
 *    to you under the Apache License, Version 2.0 (the
 *    "License"); you may not use this file except in compliance
 *    with the License.  You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing,
 *    software distributed under the License is distributed on an
 *    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
 *    KIND, either express or implied.  See the License for the
 *    specific language governing permissions and limitations
 *    under the License.
 * ====================================================================
 */

#ifndef SVN_LIBSVN_FS_FS_H
#define SVN_LIBSVN_FS_FS_H

#include <apr_pools.h>
#include <apr_hash.h>
#include <apr_network_io.h>
#include <apr_md5.h>
#include <apr_sha1.h>

#include "svn_fs.h"
#include "svn_config.h"
#include "private/svn_atomic.h"
#include "private/svn_cache.h"
#include "private/svn_fs_private.h"
#include "private/svn_sqlite.h"
#include "private/svn_mutex.h"

#include "rev_file.h"

#ifdef __cplusplus
extern "C" {
#endif /* __cplusplus */


/*** The filesystem structure.  ***/

/* Following are defines that specify the textual elements of the
   native filesystem directories and revision files. */

/* Names of special files in the fs_fs filesystem. */
#define PATH_FORMAT           "format"           /* Contains format number */
#define PATH_UUID             "uuid"             /* Contains UUID */
#define PATH_CURRENT          "current"          /* Youngest revision */
#define PATH_LOCK_FILE        "write-lock"       /* Revision lock file */
#define PATH_PACK_LOCK_FILE   "pack-lock"        /* Pack lock file */
#define PATH_REVS_DIR         "revs"             /* Directory of revisions */
#define PATH_REVPROPS_DIR     "revprops"         /* Directory of revprops */
#define PATH_TXNS_DIR         "transactions"     /* Directory of transactions in
                                                    repos w/o log addressing */
#define PATH_NODE_ORIGINS_DIR "node-origins"     /* Lazy node-origin cache */
#define PATH_TXN_PROTOS_DIR   "txn-protorevs"    /* Directory of proto-revs */
#define PATH_TXN_CURRENT      "txn-current"      /* File with next txn key */
#define PATH_TXN_CURRENT_LOCK "txn-current-lock" /* Lock for txn-current */
#define PATH_LOCKS_DIR        "locks"            /* Directory of locks */
#define PATH_MIN_UNPACKED_REV "min-unpacked-rev" /* Oldest revision which
                                                    has not been packed. */
#define PATH_REVPROP_GENERATION "revprop-generation"
                                                 /* Current revprop generation*/
#define PATH_MANIFEST         "manifest"         /* Manifest file name */
#define PATH_PACKED           "pack"             /* Packed revision data file */
#define PATH_EXT_PACKED_SHARD ".pack"            /* Extension for packed
                                                    shards */
#define PATH_EXT_L2P_INDEX    ".l2p"             /* extension of the log-
                                                    to-phys index */
#define PATH_EXT_P2L_INDEX    ".p2l"             /* extension of the phys-
                                                    to-log index */
/* If you change this, look at tests/svn_test_fs.c(maybe_install_fsfs_conf) */
#define PATH_CONFIG           "fsfs.conf"        /* Configuration */

/* Names of special files and file extensions for transactions */
#define PATH_CHANGES       "changes"       /* Records changes made so far */
#define PATH_TXN_PROPS     "props"         /* Transaction properties */
#define PATH_NEXT_IDS      "next-ids"      /* Next temporary ID assignments */
#define PATH_PREFIX_NODE   "node."         /* Prefix for node filename */
#define PATH_EXT_TXN       ".txn"          /* Extension of txn dir */
#define PATH_EXT_CHILDREN  ".children"     /* Extension for dir contents */
#define PATH_EXT_PROPS     ".props"        /* Extension for node props */
#define PATH_EXT_REV       ".rev"          /* Extension of protorev file */
#define PATH_EXT_REV_LOCK  ".rev-lock"     /* Extension of protorev lock file */
#define PATH_TXN_ITEM_INDEX "itemidx"      /* File containing the current item
                                              index number */
#define PATH_INDEX          "index"        /* name of index files w/o ext */

/* Names of files in legacy FS formats */
#define PATH_REV           "rev"           /* Proto rev file */
#define PATH_REV_LOCK      "rev-lock"      /* Proto rev (write) lock file */

/* Names of sections and options in fsfs.conf. */
#define CONFIG_SECTION_CACHES            "caches"
#define CONFIG_OPTION_FAIL_STOP          "fail-stop"
#define CONFIG_SECTION_REP_SHARING       "rep-sharing"
#define CONFIG_OPTION_ENABLE_REP_SHARING "enable-rep-sharing"
#define CONFIG_SECTION_DELTIFICATION     "deltification"
#define CONFIG_OPTION_ENABLE_DIR_DELTIFICATION   "enable-dir-deltification"
#define CONFIG_OPTION_ENABLE_PROPS_DELTIFICATION "enable-props-deltification"
#define CONFIG_OPTION_MAX_DELTIFICATION_WALK     "max-deltification-walk"
#define CONFIG_OPTION_MAX_LINEAR_DELTIFICATION   "max-linear-deltification"
#define CONFIG_OPTION_COMPRESSION_LEVEL  "compression-level"
#define CONFIG_SECTION_PACKED_REVPROPS   "packed-revprops"
#define CONFIG_OPTION_REVPROP_PACK_SIZE  "revprop-pack-size"
#define CONFIG_OPTION_COMPRESS_PACKED_REVPROPS  "compress-packed-revprops"
#define CONFIG_SECTION_IO                "io"
#define CONFIG_OPTION_BLOCK_SIZE         "block-size"
#define CONFIG_OPTION_L2P_PAGE_SIZE      "l2p-page-size"
#define CONFIG_OPTION_P2L_PAGE_SIZE      "p2l-page-size"
#define CONFIG_SECTION_DEBUG             "debug"
#define CONFIG_OPTION_PACK_AFTER_COMMIT  "pack-after-commit"
#define CONFIG_OPTION_VERIFY_BEFORE_COMMIT "verify-before-commit"
#define CONFIG_OPTION_COMPRESSION        "compression"

/* The format number of this filesystem.
   This is independent of the repository format number, and
   independent of any other FS back ends.

   Note: If you bump this, please update the switch statement in
         svn_fs_fs__create() as well.
 */
#define SVN_FS_FS__FORMAT_NUMBER   8

/* The minimum format number that supports svndiff version 1.  */
#define SVN_FS_FS__MIN_SVNDIFF1_FORMAT 2

/* The minimum format number that supports transaction ID generation
   using a transaction sequence in the txn-current file. */
#define SVN_FS_FS__MIN_TXN_CURRENT_FORMAT 3

/* The minimum format number that supports the "layout" filesystem
   format option. */
#define SVN_FS_FS__MIN_LAYOUT_FORMAT_OPTION_FORMAT 3

/* The minimum format number that stores protorevs in a separate directory. */
#define SVN_FS_FS__MIN_PROTOREVS_DIR_FORMAT 3

/* The minimum format number that doesn't keep node and copy ID counters. */
#define SVN_FS_FS__MIN_NO_GLOBAL_IDS_FORMAT 3

/* The minimum format number that maintains minfo-here and minfo-count
   noderev fields. */
#define SVN_FS_FS__MIN_MERGEINFO_FORMAT 3

/* The minimum format number that allows rep sharing. */
#define SVN_FS_FS__MIN_REP_SHARING_FORMAT 4

/* The minimum format number that supports packed shards. */
#define SVN_FS_FS__MIN_PACKED_FORMAT 4

/* The minimum format number that stores node kinds in changed-paths lists. */
#define SVN_FS_FS__MIN_KIND_IN_CHANGED_FORMAT 4

/* 1.8 deltification options should work with any FSFS repo but to avoid
 * issues with very old servers, restrict those options to the 1.6+ format*/
#define SVN_FS_FS__MIN_DELTIFICATION_FORMAT 4

/* The minimum format number that supports a configuration file (fsfs.conf) */
#define SVN_FS_FS__MIN_CONFIG_FILE 4

/* The 1.7-dev format, never released, that packed revprops into SQLite
   revprops.db . */
#define SVN_FS_FS__PACKED_REVPROP_SQLITE_DEV_FORMAT 5

/* The minimum format number that supports packed revprops. */
#define SVN_FS_FS__MIN_PACKED_REVPROP_FORMAT 6

/* The minimum format number that supports packed revprops. */
#define SVN_FS_FS__MIN_LOG_ADDRESSING_FORMAT 7

/* Minimum format number that providing a separate lock file for pack ops */
#define SVN_FS_FS__MIN_PACK_LOCK_FORMAT 7

/* Minimum format number that stores mergeinfo-mode flag in changed paths */
#define SVN_FS_FS__MIN_MERGEINFO_IN_CHANGED_FORMAT 7

/* Minimum format number that supports per-instance filesystem IDs. */
#define SVN_FS_FS__MIN_INSTANCE_ID_FORMAT 7

/* The minimum format number that supports svndiff version 2. */
#define SVN_FS_FS__MIN_SVNDIFF2_FORMAT 8

/* The minimum format number that supports the special notation ("-")
   for optional values that are not present in the representation strings,
   such as SHA1 or the uniquifier.  For example:

     15 0 563 7809 28ef320a82e7bd11eebdf3502d69e608 - 14-g/_5
 */
#define SVN_FS_FS__MIN_REP_STRING_OPTIONAL_VALUES_FORMAT 8

 /* The minimum format number that supports V2 schema of the rep-cache.db
    database. */
#define SVN_FS_FS__MIN_REP_CACHE_SCHEMA_V2_FORMAT 8

/* On most operating systems apr implements file locks per process, not
   per file.  On Windows apr implements the locking as per file handle
   locks, so we don't have to add our own mutex for just in-process
   synchronization. */
#if APR_HAS_THREADS && !defined(WIN32)
#define SVN_FS_FS__USE_LOCK_MUTEX 1
#else
#define SVN_FS_FS__USE_LOCK_MUTEX 0
#endif

/* Maximum number of changes we deliver per request when listing the
   changed paths for a given revision.   Anything > 0 will do.
   At 100..300 bytes per entry, this limits the allocation to ~30kB. */
#define SVN_FS_FS__CHANGES_BLOCK_SIZE 100

/* Private FSFS-specific data shared between all svn_txn_t objects that
   relate to a particular transaction in a filesystem (as identified
   by transaction id and filesystem UUID).  Objects of this type are
   allocated in their own subpool of the common pool. */
typedef struct fs_fs_shared_txn_data_t
{
  /* The next transaction in the list, or NULL if there is no following
     transaction. */
  struct fs_fs_shared_txn_data_t *next;

  /* ID of this transaction. */
  svn_fs_fs__id_part_t txn_id;

  /* Whether the transaction's prototype revision file is locked for
     writing by any thread in this process (including the current
     thread; recursive locks are not permitted).  This is effectively
     a non-recursive mutex. */
  svn_boolean_t being_written;

  /* The pool in which this object has been allocated; a subpool of the
     common pool. */
  apr_pool_t *pool;
} fs_fs_shared_txn_data_t;

/* Private FSFS-specific data shared between all svn_fs_t objects that
   relate to a particular filesystem, as identified by filesystem UUID.
   Objects of this type are allocated in the common pool. */
typedef struct fs_fs_shared_data_t
{
  /* A list of shared transaction objects for each transaction that is
     currently active, or NULL if none are.  All access to this list,
     including the contents of the objects stored in it, is synchronised
     under TXN_LIST_LOCK. */
  fs_fs_shared_txn_data_t *txns;

  /* A free transaction object, or NULL if there is no free object.
     Access to this object is synchronised under TXN_LIST_LOCK. */
  fs_fs_shared_txn_data_t *free_txn;

  /* The following lock must be taken out in reverse order of their
     declaration here.  Any subset may be acquired and held at any given
     time but their relative acquisition order must not change.

     (lock 'txn-current' before 'pack' before 'write' before 'txn-list') */

  /* A lock for intra-process synchronization when accessing the TXNS list. */
  svn_mutex__t *txn_list_lock;

  /* A lock for intra-process synchronization when grabbing the
     repository write lock. */
  svn_mutex__t *fs_write_lock;

  /* A lock for intra-process synchronization when grabbing the
     repository pack operation lock. */
  svn_mutex__t *fs_pack_lock;

  /* A lock for intra-process synchronization when locking the
     txn-current file. */
  svn_mutex__t *txn_current_lock;

  /* The common pool, under which this object is allocated, subpools
     of which are used to allocate the transaction objects. */
  apr_pool_t *common_pool;
} fs_fs_shared_data_t;

/* Data structure for the 1st level DAG node cache. */
typedef struct fs_fs_dag_cache_t fs_fs_dag_cache_t;

/* Key type for all caches that use revision + offset / counter as key.

   Note: Cache keys should be 16 bytes for best performance and there
         should be no padding. */
typedef struct pair_cache_key_t
{
  /* The object's revision.  Use the 64 data type to prevent padding. */
  apr_int64_t revision;

  /* Sub-address: item index, revprop generation, packed flag, etc. */
  apr_int64_t second;
} pair_cache_key_t;

/* Key type that identifies a txdelta window.

   Note: Cache keys should require no padding. */
typedef struct window_cache_key_t
{
  /* The object's revision.  Use the 64 data type to prevent padding. */
  apr_int64_t revision;

  /* Window number within that representation. */
  apr_int64_t chunk_index;

  /* Item index of the representation */
  apr_uint64_t item_index;
} window_cache_key_t;

typedef enum compression_type_t
{
  compression_type_none,
  compression_type_zlib,
  compression_type_lz4
} compression_type_t;

/* Private (non-shared) FSFS-specific data for each svn_fs_t object.
   Any caches in here may be NULL. */
typedef struct fs_fs_data_t
{
  /* The format number of this FS. */
  int format;

  /* The maximum number of files to store per directory (for sharded
     layouts) or zero (for linear layouts). */
  int max_files_per_dir;

  /* If set, this FS is using logical addressing. Otherwise, it is using
     physical addressing. */
  svn_boolean_t use_log_addressing;

  /* Rev / pack file read granularity in bytes. */
  apr_int64_t block_size;

  /* Capacity in entries of log-to-phys index pages */
  apr_int64_t l2p_page_size;

  /* Rev / pack file granularity (in bytes) covered by a single phys-to-log
   * index page. */
  apr_int64_t p2l_page_size;

  /* If set, parse and cache *all* data of each block that we read
   * (not just the one bit that we need, atm). */
  svn_boolean_t use_block_read;

  /* The revision that was youngest, last time we checked. */
  svn_revnum_t youngest_rev_cache;

  /* Caches of immutable data.  (Note that these may be shared between
     multiple svn_fs_t's for the same filesystem.) */

  /* Access to the configured memcached instances.  May be NULL. */
  svn_memcache_t *memcache;

  /* If TRUE, don't ignore any cache-related errors.  If FALSE, errors from
     e.g. memcached may be ignored as caching is an optional feature. */
  svn_boolean_t fail_stop;

  /* A cache of revision root IDs, mapping from (svn_revnum_t *) to
     (svn_fs_id_t *).  (Not threadsafe.) */
  svn_cache__t *rev_root_id_cache;

  /* Caches native dag_node_t* instances and acts as a 1st level cache */
  fs_fs_dag_cache_t *dag_node_cache;

  /* DAG node cache for immutable nodes.  Maps (revision, fspath)
     to (dag_node_t *). This is the 2nd level cache for DAG nodes. */
  svn_cache__t *rev_node_cache;

  /* A cache of the contents of immutable directories; maps from
     unparsed FS ID to a apr_hash_t * mapping (const char *) dirent
     names to (svn_fs_dirent_t *). */
  svn_cache__t *dir_cache;

  /* Fulltext cache; currently only used with memcached.  Maps from
     rep key (revision/offset) to svn_stringbuf_t. */
  svn_cache__t *fulltext_cache;

  /* The current prefix to be used for revprop cache entries.
     If this is 0, a new unique prefix must be chosen. */
  apr_uint64_t revprop_prefix;

  /* Revision property cache.  Maps from (rev,prefix) to apr_hash_t.
     Unparsed svn_string_t representations of the serialized hash
     will be written to the cache but the getter returns apr_hash_t. */
  svn_cache__t *revprop_cache;

  /* Node properties cache.  Maps from rep key to apr_hash_t. */
  svn_cache__t *properties_cache;

  /* Pack manifest cache; a cache mapping (svn_revnum_t) shard number to
     a manifest; and a manifest is a mapping from (svn_revnum_t) revision
     number offset within a shard to (apr_off_t) byte-offset in the
     respective pack file. */
  svn_cache__t *packed_offset_cache;

  /* Cache for svn_fs_fs__raw_cached_window_t objects; the key is
     window_cache_key_t. */
  svn_cache__t *raw_window_cache;

  /* Cache for txdelta_window_t objects; the key is window_cache_key_t */
  svn_cache__t *txdelta_window_cache;

  /* Cache for combined windows as svn_stringbuf_t objects;
     the key is window_cache_key_t */
  svn_cache__t *combined_window_cache;

  /* Cache for node_revision_t objects; the key is (revision, item_index) */
  svn_cache__t *node_revision_cache;

  /* Cache for change lists n blocks as svn_fs_fs__changes_list_t * objects;
     the key is the (revision, first-element-in-block) pair. */
  svn_cache__t *changes_cache;

  /* Cache for svn_fs_fs__rep_header_t objects; the key is a
     (revision, item index) pair */
  svn_cache__t *rep_header_cache;

  /* Cache for svn_mergeinfo_t objects; the key is a combination of
     revision, inheritance flags and path. */
  svn_cache__t *mergeinfo_cache;

  /* Cache for presence of svn_mergeinfo_t on a noderev; the key is a
     combination of revision, inheritance flags and path; value is "1"
     if the node has mergeinfo, "0" if it doesn't. */
  svn_cache__t *mergeinfo_existence_cache;

  /* Cache for l2p_header_t objects; the key is (revision, is-packed).
     Will be NULL for pre-format7 repos */
  svn_cache__t *l2p_header_cache;

  /* Cache for l2p_page_t objects; the key is svn_fs_fs__page_cache_key_t.
     Will be NULL for pre-format7 repos */
  svn_cache__t *l2p_page_cache;

  /* Cache for p2l_header_t objects; the key is (revision, is-packed).
     Will be NULL for pre-format7 repos */
  svn_cache__t *p2l_header_cache;

  /* Cache for apr_array_header_t objects containing svn_fs_fs__p2l_entry_t
     elements; the key is svn_fs_fs__page_cache_key_t.
     Will be NULL for pre-format7 repos */
  svn_cache__t *p2l_page_cache;

  /* TRUE while the we hold a lock on the write lock file. */
  svn_boolean_t has_write_lock;

  /* If set, there are or have been more than one concurrent transaction */
  svn_boolean_t concurrent_transactions;

  /* Temporary cache for changed directories yet to be committed; maps from
     unparsed FS ID to ###x.  NULL outside transactions. */
  svn_cache__t *txn_dir_cache;

  /* Data shared between all svn_fs_t objects for a given filesystem. */
  fs_fs_shared_data_t *shared;

  /* The sqlite database used for rep caching. */
  svn_sqlite__db_t *rep_cache_db;

  /* Thread-safe boolean */
  svn_atomic_t rep_cache_db_opened;

  /* The oldest revision not in a pack file.  It also applies to revprops
   * if revprop packing has been enabled by the FSFS format version. */
  svn_revnum_t min_unpacked_rev;

  /* Whether rep-sharing is supported by the filesystem
   * and allowed by the configuration. */
  svn_boolean_t rep_sharing_allowed;

  /* File size limit in bytes up to which multiple revprops shall be packed
   * into a single file. */
  apr_int64_t revprop_pack_size;

  /* Whether packed revprop files shall be compressed. */
  svn_boolean_t compress_packed_revprops;

  /* Whether directory nodes shall be deltified just like file nodes. */
  svn_boolean_t deltify_directories;

  /* Whether nodes properties shall be deltified. */
  svn_boolean_t deltify_properties;

  /* Restart deltification histories after each multiple of this value */
  apr_int64_t max_deltification_walk;

  /* Maximum number of length of the linear part at the top of the
   * deltification history after which skip deltas will be used. */
  apr_int64_t max_linear_deltification;

  /* Compression type to use with txdelta storage format in new revs. */
  compression_type_t delta_compression_type;

  /* Compression level (currently, only used with compression_type_zlib). */
  int delta_compression_level;

  /* Pack after every commit. */
  svn_boolean_t pack_after_commit;

  /* Verify each new revision before commit. */
  svn_boolean_t verify_before_commit;

  /* Per-instance filesystem ID, which provides an additional level of
     uniqueness for filesystems that share the same UUID, but should
     still be distinguishable (e.g. backups produced by svn_fs_hotcopy()
     or dump / load cycles). */
  const char *instance_id;

  /* Ensure that all filesystem changes are written to disk. */
  svn_boolean_t flush_to_disk;

  /* Pointer to svn_fs_open. */
  svn_error_t *(*svn_fs_open_)(svn_fs_t **, const char *, apr_hash_t *,
                               apr_pool_t *, apr_pool_t *);
} fs_fs_data_t;


/*** Filesystem Transaction ***/
typedef struct transaction_t
{
  /* node revision id of the root node.  */
  const svn_fs_id_t *root_id;

  /* node revision id of the node which is the root of the revision
     upon which this txn is base.  (unfinished only) */
  const svn_fs_id_t *base_id;

  /* copies list (const char * copy_ids), or NULL if there have been
     no copies in this transaction.  */
  apr_array_header_t *copies;

} transaction_t;


/*** Representation ***/
/* If you add fields to this, check to see if you need to change
 * svn_fs_fs__rep_copy. */
typedef struct representation_t
{
  /* Checksums digests for the contents produced by this representation.
     This checksum is for the contents the rep shows to consumers,
     regardless of how the rep stores the data under the hood.  It is
     independent of the storage (fulltext, delta, whatever).

     If has_sha1 is FALSE, then for compatibility behave as though this
     checksum matches the expected checksum.

     The md5 checksum is always filled, unless this is rep which was
     retrieved from the rep-cache.  The sha1 checksum is only computed on
     a write, for use with rep-sharing. */
  svn_boolean_t has_sha1;
  unsigned char sha1_digest[APR_SHA1_DIGESTSIZE];
  unsigned char md5_digest[APR_MD5_DIGESTSIZE];

  /* Revision where this representation is located. */
  svn_revnum_t revision;

  /* Item index with the revision. */
  apr_uint64_t item_index;

  /* The size of the representation in bytes as seen in the revision
     file. */
  svn_filesize_t size;

  /* The size of the fulltext of the representation. If this is 0,
   * for a plain rep, the real fulltext size is equal to the SIZE field.
   * For a delta rep, this field is always the real fulltext size.
   *
   * Note that svn_fs_fs__fixup_expanded_size() checks for these special
   * cases and ensures that this field contains the actual value.  We call
   * it early after reading a representation struct, so most code does not
   * have to worry about it.
   */
  svn_filesize_t expanded_size;

  /* Is this a representation (still) within a transaction? */
  svn_fs_fs__id_part_t txn_id;

  /* For rep-sharing, we need a way of uniquifying node-revs which share the
     same representation (see svn_fs_fs__noderev_same_rep_key() ).  So, we
     store the original txn of the node rev (not the rep!), along with some
     intra-node uniqification content. */
  struct
    {
      /* unique context, i.e. txn ID, in which the noderev (!) got created */
      svn_fs_fs__id_part_t noderev_txn_id;

      /* unique value within that txn */
      apr_uint64_t number;
    } uniquifier;
} representation_t;


/*** Node-Revision ***/
/* If you add fields to this, check to see if you need to change
 * copy_node_revision in dag.c. */
typedef struct node_revision_t
{
  /* node kind */
  svn_node_kind_t kind;

  /* The node-id for this node-rev. */
  const svn_fs_id_t *id;

  /* predecessor node revision id, or NULL if there is no predecessor
     for this node revision */
  const svn_fs_id_t *predecessor_id;

  /* If this node-rev is a copy, where was it copied from? */
  const char *copyfrom_path;
  svn_revnum_t copyfrom_rev;

  /* Helper for history tracing, root of the parent tree from whence
     this node-rev was copied. */
  svn_revnum_t copyroot_rev;
  const char *copyroot_path;

  /* Number of predecessors this node revision has (recursively).
     A difference from the BDB backend is that it cannot be -1. */
  int predecessor_count;

  /* representation key for this node's properties.  may be NULL if
     there are no properties.  */
  representation_t *prop_rep;

  /* representation for this node's data.  may be NULL if there is
     no data. */
  representation_t *data_rep;

  /* path at which this node first came into existence.  */
  const char *created_path;

  /* is this the unmodified root of a transaction? */
  svn_boolean_t is_fresh_txn_root;

  /* Number of nodes with svn:mergeinfo properties that are
     descendants of this node (including it itself) */
  apr_int64_t mergeinfo_count;

  /* Does this node itself have svn:mergeinfo? */
  svn_boolean_t has_mergeinfo;

} node_revision_t;


/*** Change ***/
typedef struct change_t
{
  /* Path of the change. */
  svn_string_t path;

  /* API compatible change description */
  svn_fs_path_change2_t info;
} change_t;


/*** Context for reading changed paths lists iteratively. */
typedef struct svn_fs_fs__changes_context_t
{
  /* Repository to fetch from. */
  svn_fs_t *fs;

  /* Revision that we read from. */
  svn_revnum_t revision;

  /* Revision file object to use when needed.  NULL until the first access. */
  svn_fs_fs__revision_file_t *revision_file;

  /* Pool to create REVISION_FILE in. */
  apr_pool_t *rev_file_pool;

  /* Index of the next change to fetch. */
  apr_size_t next;

  /* Offset, within the changed paths list on disk, of the next change to
     fetch. */
  apr_off_t next_offset;

  /* Has the end of the list been reached? */
  svn_boolean_t eol;

} svn_fs_fs__changes_context_t;

/*** Directory (only used at the cache interface) ***/
typedef struct svn_fs_fs__dir_data_t
{
  /* Contents, i.e. all directory entries, sorted by name. */
  apr_array_header_t *entries;

  /* SVN_INVALID_FILESIZE for committed data, otherwise the length of the
   * in-txn on-disk representation of that directory. */
  svn_filesize_t txn_filesize;
} svn_fs_fs__dir_data_t;


#ifdef __cplusplus
}
#endif /* __cplusplus */

#endif /* SVN_LIBSVN_FS_FS_H */