X-Git-Url: http://git.onelab.eu/?a=blobdiff_plain;f=ovsdb%2Ffile.c;h=7c8ac6f292a87daa22f91adc4955e2a4ccdf99de;hb=cfc50ae514f805dcd9c14589f21158185424daf6;hp=4883d76f1b2144f78acc40ef17cad814c656f728;hpb=f85f8ebbfac946c19b3c6eb0f4170f579d0a4d25;p=sliver-openvswitch.git

diff --git a/ovsdb/file.c b/ovsdb/file.c
index 4883d76f1..7c8ac6f29 100644
--- a/ovsdb/file.c
+++ b/ovsdb/file.c
@@ -1,4 +1,4 @@
-/* Copyright (c) 2009 Nicira Networks
+/* Copyright (c) 2009, 2010, 2011, 2012, 2013 Nicira, Inc.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -17,344 +17,771 @@
 
 #include "file.h"
 
-#include <assert.h>
 #include <errno.h>
 #include <fcntl.h>
-#include <stdlib.h>
-#include <string.h>
 #include <unistd.h>
 
+#include "bitmap.h"
+#include "column.h"
+#include "log.h"
 #include "json.h"
 #include "lockfile.h"
+#include "ovsdb.h"
 #include "ovsdb-error.h"
-#include "sha1.h"
+#include "row.h"
+#include "socket-util.h"
+#include "table.h"
+#include "timeval.h"
+#include "transaction.h"
+#include "uuid.h"
 #include "util.h"
-
-#define THIS_MODULE VLM_ovsdb_file
 #include "vlog.h"
 
-enum ovsdb_file_mode {
-    OVSDB_FILE_READ,
-    OVSDB_FILE_WRITE
-};
+VLOG_DEFINE_THIS_MODULE(ovsdb_file);
 
-struct ovsdb_file {
-    off_t offset;
-    char *name;
-    struct lockfile *lockfile;
-    FILE *stream;
-    struct ovsdb_error *read_error;
-    struct ovsdb_error *write_error;
-    enum ovsdb_file_mode mode;
+/* Minimum number of milliseconds between database compactions. */
+#define COMPACT_MIN_MSEC        (10 * 60 * 1000) /* 10 minutes. */
+
+/* Minimum number of milliseconds between trying to compact the database if
+ * compacting fails. */
+#define COMPACT_RETRY_MSEC      (60 * 1000)      /* 1 minute. */
+
+/* A transaction being converted to JSON for writing to a file. */
+struct ovsdb_file_txn {
+    struct json *json;          /* JSON for the whole transaction. */
+    struct json *table_json;    /* JSON for 'table''s transaction. */
+    struct ovsdb_table *table;  /* Table described in 'table_json'.  */
 };
 
+static void ovsdb_file_txn_init(struct ovsdb_file_txn *);
+static void ovsdb_file_txn_add_row(struct ovsdb_file_txn *,
+                                   const struct ovsdb_row *old,
+                                   const struct ovsdb_row *new,
+                                   const unsigned long int *changed);
+static struct ovsdb_error *ovsdb_file_txn_commit(struct json *,
+                                                 const char *comment,
+                                                 bool durable,
+                                                 struct ovsdb_log *);
+
+static struct ovsdb_error *ovsdb_file_open__(const char *file_name,
+                                             const struct ovsdb_schema *,
+                                             bool read_only, struct ovsdb **,
+                                             struct ovsdb_file **);
+static struct ovsdb_error *ovsdb_file_txn_from_json(
+    struct ovsdb *, const struct json *, bool converting, struct ovsdb_txn **);
+static struct ovsdb_error *ovsdb_file_create(struct ovsdb *,
+                                             struct ovsdb_log *,
+                                             const char *file_name,
+                                             unsigned int n_transactions,
+                                             struct ovsdb_file **filep);
+
+/* Opens database 'file_name' and stores a pointer to the new database in
+ * '*dbp'.  If 'read_only' is false, then the database will be locked and
+ * changes to the database will be written to disk.  If 'read_only' is true,
+ * the database will not be locked and changes to the database will persist
+ * only as long as the "struct ovsdb".
+ *
+ * If 'filep' is nonnull and 'read_only' is false, then on success sets
+ * '*filep' to an ovsdb_file that represents the open file.  This ovsdb_file
+ * persists until '*dbp' is destroyed.
+ *
+ * On success, returns NULL.  On failure, returns an ovsdb_error (which the
+ * caller must destroy) and sets '*dbp' and '*filep' to NULL. */
 struct ovsdb_error *
-ovsdb_file_open(const char *name, int flags, struct ovsdb_file **filep)
+ovsdb_file_open(const char *file_name, bool read_only,
+                struct ovsdb **dbp, struct ovsdb_file **filep)
 {
-    struct lockfile *lockfile;
+    return ovsdb_file_open__(file_name, NULL, read_only, dbp, filep);
+}
+
+/* Opens database 'file_name' with an alternate schema.  The specified 'schema'
+ * is used to interpret the data in 'file_name', ignoring the schema actually
+ * stored in the file.  Data in the file for tables or columns that do not
+ * exist in 'schema' are ignored, but the ovsdb file format must otherwise be
+ * observed, including column constraints.
+ *
+ * This function can be useful for upgrading or downgrading databases to
+ * "almost-compatible" formats.
+ *
+ * The database will not be locked.  Changes to the database will persist only
+ * as long as the "struct ovsdb".
+ *
+ * On success, stores a pointer to the new database in '*dbp' and returns a
+ * null pointer.  On failure, returns an ovsdb_error (which the caller must
+ * destroy) and sets '*dbp' to NULL. */
+struct ovsdb_error *
+ovsdb_file_open_as_schema(const char *file_name,
+                          const struct ovsdb_schema *schema,
+                          struct ovsdb **dbp)
+{
+    return ovsdb_file_open__(file_name, schema, true, dbp, NULL);
+}
+
+static struct ovsdb_error *
+ovsdb_file_open_log(const char *file_name, enum ovsdb_log_open_mode open_mode,
+                    struct ovsdb_log **logp, struct ovsdb_schema **schemap)
+{
+    struct ovsdb_schema *schema = NULL;
+    struct ovsdb_log *log = NULL;
     struct ovsdb_error *error;
-    struct ovsdb_file *file;
-    struct stat s;
-    FILE *stream;
-    int accmode;
-    int fd;
-
-    *filep = NULL;
-
-    accmode = flags & O_ACCMODE;
-    if (accmode == O_RDWR || accmode == O_WRONLY) {
-        int retval = lockfile_lock(name, 0, &lockfile);
-        if (retval) {
-            error = ovsdb_io_error(retval, "%s: failed to lock lockfile",
-                                   name);
+    struct json *json = NULL;
+
+    ovs_assert(logp || schemap);
+
+    error = ovsdb_log_open(file_name, open_mode, -1, &log);
+    if (error) {
+        goto error;
+    }
+
+    error = ovsdb_log_read(log, &json);
+    if (error) {
+        goto error;
+    } else if (!json) {
+        error = ovsdb_io_error(EOF, "%s: database file contains no schema",
+                               file_name);
+        goto error;
+    }
+
+    if (schemap) {
+        error = ovsdb_schema_from_json(json, &schema);
+        if (error) {
+            error = ovsdb_wrap_error(error,
+                                     "failed to parse \"%s\" as ovsdb schema",
+                                     file_name);
             goto error;
         }
+    }
+    json_destroy(json);
+
+    if (logp) {
+        *logp = log;
     } else {
-        lockfile = NULL;
+        ovsdb_log_close(log);
     }
+    if (schemap) {
+        *schemap = schema;
+    }
+    return NULL;
 
-    fd = open(name, flags, 0666);
-    if (fd < 0) {
-        const char *op = flags & O_CREAT && flags & O_EXCL ? "create" : "open";
-        error = ovsdb_io_error(errno, "%s: %s failed", op, name);
-        goto error_unlock;
+error:
+    ovsdb_log_close(log);
+    json_destroy(json);
+    if (logp) {
+        *logp = NULL;
+    }
+    if (schemap) {
+        *schemap = NULL;
     }
+    return error;
+}
 
-    if (!fstat(fd, &s) && s.st_size == 0) {
-        /* It's (probably) a new file so fsync() its parent directory to ensure
-         * that its directory entry is committed to disk. */
-        char *dir = dir_name(name);
-        int dirfd = open(dir, O_RDONLY);
-        if (dirfd >= 0) {
-            if (fsync(dirfd) && errno != EINVAL) {
-                VLOG_ERR("%s: fsync failed (%s)", dir, strerror(errno));
-            }
-            close(dirfd);
-        } else {
-            VLOG_ERR("%s: open failed (%s)", dir, strerror(errno));
+static struct ovsdb_error *
+ovsdb_file_open__(const char *file_name,
+                  const struct ovsdb_schema *alternate_schema,
+                  bool read_only, struct ovsdb **dbp,
+                  struct ovsdb_file **filep)
+{
+    enum ovsdb_log_open_mode open_mode;
+    unsigned int n_transactions;
+    struct ovsdb_schema *schema = NULL;
+    struct ovsdb_error *error;
+    struct ovsdb_log *log;
+    struct json *json;
+    struct ovsdb *db = NULL;
+
+    /* In read-only mode there is no ovsdb_file so 'filep' must be null. */
+    ovs_assert(!(read_only && filep));
+
+    open_mode = read_only ? OVSDB_LOG_READ_ONLY : OVSDB_LOG_READ_WRITE;
+    error = ovsdb_file_open_log(file_name, open_mode, &log,
+                                alternate_schema ? NULL : &schema);
+    if (error) {
+        goto error;
+    }
+
+    db = ovsdb_create(schema ? schema : ovsdb_schema_clone(alternate_schema));
+
+    n_transactions = 0;
+    while ((error = ovsdb_log_read(log, &json)) == NULL && json) {
+        struct ovsdb_txn *txn;
+
+        error = ovsdb_file_txn_from_json(db, json, alternate_schema != NULL,
+                                         &txn);
+        json_destroy(json);
+        if (error) {
+            ovsdb_log_unread(log);
+            break;
+        }
+
+        n_transactions++;
+        error = ovsdb_txn_commit(txn, false);
+        if (error) {
+            ovsdb_log_unread(log);
+            break;
         }
-        free(dir);
     }
+    if (error) {
+        /* Log error but otherwise ignore it.  Probably the database just got
+         * truncated due to power failure etc. and we should use its current
+         * contents. */
+        char *msg = ovsdb_error_to_string(error);
+        VLOG_ERR("%s", msg);
+        free(msg);
+
+        ovsdb_error_destroy(error);
+    }
+
+    if (!read_only) {
+        struct ovsdb_file *file;
 
-    stream = fdopen(fd, (accmode == O_RDONLY ? "rb"
-                         : accmode == O_WRONLY ? "wb"
-                         : "w+b"));
-    if (!stream) {
-        error = ovsdb_io_error(errno, "%s: fdopen failed", name);
-        goto error_close;
+        error = ovsdb_file_create(db, log, file_name, n_transactions, &file);
+        if (error) {
+            goto error;
+        }
+        if (filep) {
+            *filep = file;
+        }
+    } else {
+        ovsdb_log_close(log);
     }
 
-    file = xmalloc(sizeof *file);
-    file->name = xstrdup(name);
-    file->lockfile = lockfile;
-    file->stream = stream;
-    file->offset = 0;
-    file->read_error = NULL;
-    file->write_error = NULL;
-    file->mode = OVSDB_FILE_READ;
-    *filep = file;
+    *dbp = db;
     return NULL;
 
-error_close:
-    close(fd);
-error_unlock:
-    lockfile_unlock(lockfile);
 error:
+    *dbp = NULL;
+    if (filep) {
+        *filep = NULL;
+    }
+    ovsdb_destroy(db);
+    ovsdb_log_close(log);
     return error;
 }
 
-void
-ovsdb_file_close(struct ovsdb_file *file)
+static struct ovsdb_error *
+ovsdb_file_update_row_from_json(struct ovsdb_row *row, bool converting,
+                                const struct json *json)
 {
-    if (file) {
-        free(file->name);
-        fclose(file->stream);
-        lockfile_unlock(file->lockfile);
-        ovsdb_error_destroy(file->read_error);
-        ovsdb_error_destroy(file->write_error);
-        free(file);
+    struct ovsdb_table_schema *schema = row->table->schema;
+    struct ovsdb_error *error;
+    struct shash_node *node;
+
+    if (json->type != JSON_OBJECT) {
+        return ovsdb_syntax_error(json, NULL, "row must be JSON object");
     }
-}
 
-static const char magic[] = "OVSDB JSON ";
+    SHASH_FOR_EACH (node, json_object(json)) {
+        const char *column_name = node->name;
+        const struct ovsdb_column *column;
+        struct ovsdb_datum datum;
 
-static bool
-parse_header(char *header, unsigned long int *length,
-             uint8_t sha1[SHA1_DIGEST_SIZE])
-{
-    char *p;
+        column = ovsdb_table_schema_get_column(schema, column_name);
+        if (!column) {
+            if (converting) {
+                continue;
+            }
+            return ovsdb_syntax_error(json, "unknown column",
+                                      "No column %s in table %s.",
+                                      column_name, schema->name);
+        }
 
-    /* 'header' must consist of a magic string... */
-    if (strncmp(header, magic, strlen(magic))) {
-        return false;
+        error = ovsdb_datum_from_json(&datum, &column->type, node->data, NULL);
+        if (error) {
+            return error;
+        }
+        ovsdb_datum_swap(&row->fields[column->index], &datum);
+        ovsdb_datum_destroy(&datum, &column->type);
     }
 
-    /* ...followed by a length in bytes... */
-    *length = strtoul(header + strlen(magic), &p, 10);
-    if (!*length || *length == ULONG_MAX || *p != ' ') {
-        return false;
+    return NULL;
+}
+
+static struct ovsdb_error *
+ovsdb_file_txn_row_from_json(struct ovsdb_txn *txn, struct ovsdb_table *table,
+                             bool converting,
+                             const struct uuid *row_uuid, struct json *json)
+{
+    const struct ovsdb_row *row = ovsdb_table_get_row(table, row_uuid);
+    if (json->type == JSON_NULL) {
+        if (!row) {
+            return ovsdb_syntax_error(NULL, NULL, "transaction deletes "
+                                      "row "UUID_FMT" that does not exist",
+                                      UUID_ARGS(row_uuid));
+        }
+        ovsdb_txn_row_delete(txn, row);
+        return NULL;
+    } else if (row) {
+        return ovsdb_file_update_row_from_json(ovsdb_txn_row_modify(txn, row),
+                                               converting, json);
+    } else {
+        struct ovsdb_error *error;
+        struct ovsdb_row *new;
+
+        new = ovsdb_row_create(table);
+        *ovsdb_row_get_uuid_rw(new) = *row_uuid;
+        error = ovsdb_file_update_row_from_json(new, converting, json);
+        if (error) {
+            ovsdb_row_destroy(new);
+        } else {
+            ovsdb_txn_row_insert(txn, new);
+        }
+        return error;
     }
-    p++;
+}
 
-    /* ...followed by a SHA-1 hash... */
-    if (!sha1_from_hex(sha1, p)) {
-        return false;
+static struct ovsdb_error *
+ovsdb_file_txn_table_from_json(struct ovsdb_txn *txn,
+                               struct ovsdb_table *table,
+                               bool converting, struct json *json)
+{
+    struct shash_node *node;
+
+    if (json->type != JSON_OBJECT) {
+        return ovsdb_syntax_error(json, NULL, "object expected");
     }
-    p += SHA1_HEX_DIGEST_LEN;
 
-    /* ...and ended by a new-line. */
-    if (*p != '\n') {
-        return false;
+    SHASH_FOR_EACH (node, json->u.object) {
+        const char *uuid_string = node->name;
+        struct json *txn_row_json = node->data;
+        struct ovsdb_error *error;
+        struct uuid row_uuid;
+
+        if (!uuid_from_string(&row_uuid, uuid_string)) {
+            return ovsdb_syntax_error(json, NULL, "\"%s\" is not a valid UUID",
+                                      uuid_string);
+        }
+
+        error = ovsdb_file_txn_row_from_json(txn, table, converting,
+                                             &row_uuid, txn_row_json);
+        if (error) {
+            return error;
+        }
     }
 
-    return true;
+    return NULL;
 }
 
-struct ovsdb_file_read_cbdata {
-    char input[4096];
-    struct ovsdb_file *file;
-    int error;
-    unsigned long length;
-};
-
+/* Converts 'json' to an ovsdb_txn for 'db', storing the new transaction in
+ * '*txnp'.  Returns NULL if successful, otherwise an error.
+ *
+ * If 'converting' is true, then unknown table and column names are ignored
+ * (which can ease upgrading and downgrading schemas); otherwise, they are
+ * treated as errors. */
 static struct ovsdb_error *
-parse_body(struct ovsdb_file *file, off_t offset, unsigned long int length,
-           uint8_t sha1[SHA1_DIGEST_SIZE], struct json **jsonp)
+ovsdb_file_txn_from_json(struct ovsdb *db, const struct json *json,
+                         bool converting, struct ovsdb_txn **txnp)
 {
-    unsigned long int bytes_left;
-    struct json_parser *parser;
-    struct sha1_ctx ctx;
-
-    sha1_init(&ctx);
-    parser = json_parser_create(JSPF_TRAILER);
-
-    bytes_left = length;
-    while (length > 0) {
-        char input[BUFSIZ];
-        int chunk;
-
-        chunk = MIN(length, sizeof input);
-        if (fread(input, 1, chunk, file->stream) != chunk) {
-            json_parser_abort(parser);
-            return ovsdb_io_error(ferror(file->stream) ? errno : EOF,
-                                  "%s: error reading %lu bytes "
-                                  "starting at offset %lld", file->name,
-                                  length, (long long int) offset);
-        }
-        sha1_update(&ctx, input, chunk);
-        json_parser_feed(parser, input, chunk);
-        length -= chunk;
+    struct ovsdb_error *error;
+    struct shash_node *node;
+    struct ovsdb_txn *txn;
+
+    *txnp = NULL;
+
+    if (json->type != JSON_OBJECT) {
+        return ovsdb_syntax_error(json, NULL, "object expected");
     }
 
-    sha1_final(&ctx, sha1);
-    *jsonp = json_parser_finish(parser);
+    txn = ovsdb_txn_create(db);
+    SHASH_FOR_EACH (node, json->u.object) {
+        const char *table_name = node->name;
+        struct json *node_json = node->data;
+        struct ovsdb_table *table;
+
+        table = shash_find_data(&db->tables, table_name);
+        if (!table) {
+            if (!strcmp(table_name, "_date")
+                && node_json->type == JSON_INTEGER) {
+                continue;
+            } else if (!strcmp(table_name, "_comment") || converting) {
+                continue;
+            }
+
+            error = ovsdb_syntax_error(json, "unknown table",
+                                       "No table named %s.", table_name);
+            goto error;
+        }
+
+        error = ovsdb_file_txn_table_from_json(txn, table, converting,
+                                               node_json);
+        if (error) {
+            goto error;
+        }
+    }
+    *txnp = txn;
     return NULL;
+
+error:
+    ovsdb_txn_abort(txn);
+    return error;
 }
 
-struct ovsdb_error *
-ovsdb_file_read(struct ovsdb_file *file, struct json **jsonp)
+static struct ovsdb_error *
+ovsdb_file_save_copy__(const char *file_name, int locking,
+                       const char *comment, const struct ovsdb *db,
+                       struct ovsdb_log **logp)
 {
-    uint8_t expected_sha1[SHA1_DIGEST_SIZE];
-    uint8_t actual_sha1[SHA1_DIGEST_SIZE];
+    const struct shash_node *node;
+    struct ovsdb_file_txn ftxn;
     struct ovsdb_error *error;
-    off_t data_offset;
-    unsigned long data_length;
+    struct ovsdb_log *log;
     struct json *json;
-    char header[128];
 
-    *jsonp = json = NULL;
+    error = ovsdb_log_open(file_name, OVSDB_LOG_CREATE, locking, &log);
+    if (error) {
+        return error;
+    }
 
-    if (file->read_error) {
-        return ovsdb_error_clone(file->read_error);
-    } else if (file->mode == OVSDB_FILE_WRITE) {
-        return OVSDB_BUG("reading file in write mode");
+    /* Write schema. */
+    json = ovsdb_schema_to_json(db->schema);
+    error = ovsdb_log_write(log, json);
+    json_destroy(json);
+    if (error) {
+        goto exit;
     }
 
-    if (!fgets(header, sizeof header, file->stream)) {
-        if (feof(file->stream)) {
-            error = NULL;
-        } else {
-            error = ovsdb_io_error(errno, "%s: read failed", file->name);
+    /* Write data. */
+    ovsdb_file_txn_init(&ftxn);
+    SHASH_FOR_EACH (node, &db->tables) {
+        const struct ovsdb_table *table = node->data;
+        const struct ovsdb_row *row;
+
+        HMAP_FOR_EACH (row, hmap_node, &table->rows) {
+            ovsdb_file_txn_add_row(&ftxn, NULL, row, NULL);
         }
-        goto error;
     }
+    error = ovsdb_file_txn_commit(ftxn.json, comment, true, log);
 
-    if (!parse_header(header, &data_length, expected_sha1)) {
-        error = ovsdb_syntax_error(NULL, NULL, "%s: parse error at offset "
-                                   "%lld in header line \"%.*s\"",
-                                   file->name, (long long int) file->offset,
-                                   (int) strcspn(header, "\n"), header);
-        goto error;
+exit:
+    if (logp) {
+        if (!error) {
+            *logp = log;
+            log = NULL;
+        } else {
+            *logp = NULL;
+        }
     }
-
-    data_offset = file->offset + strlen(header);
-    error = parse_body(file, data_offset, data_length, actual_sha1, &json);
+    ovsdb_log_close(log);
     if (error) {
-        goto error;
+        remove(file_name);
     }
+    return error;
+}
 
-    if (memcmp(expected_sha1, actual_sha1, SHA1_DIGEST_SIZE)) {
-        error = ovsdb_syntax_error(NULL, NULL, "%s: %lu bytes starting at "
-                                   "offset %lld have SHA-1 hash "SHA1_FMT" "
-                                   "but should have hash "SHA1_FMT,
-                                   file->name, data_length,
-                                   (long long int) data_offset,
-                                   SHA1_ARGS(actual_sha1),
-                                   SHA1_ARGS(expected_sha1));
-        goto error;
+/* Saves a snapshot of 'db''s current contents as 'file_name'.  If 'comment' is
+ * nonnull, then it is added along with the data contents and can be viewed
+ * with "ovsdb-tool show-log".
+ *
+ * 'locking' is passed along to ovsdb_log_open() untouched. */
+struct ovsdb_error *
+ovsdb_file_save_copy(const char *file_name, int locking,
+                     const char *comment, const struct ovsdb *db)
+{
+    return ovsdb_file_save_copy__(file_name, locking, comment, db, NULL);
+}
+
+/* Opens database 'file_name', reads its schema, and closes it.  On success,
+ * stores the schema into '*schemap' and returns NULL; the caller then owns the
+ * schema.  On failure, returns an ovsdb_error (which the caller must destroy)
+ * and sets '*dbp' to NULL. */
+struct ovsdb_error *
+ovsdb_file_read_schema(const char *file_name, struct ovsdb_schema **schemap)
+{
+    ovs_assert(schemap != NULL);
+    return ovsdb_file_open_log(file_name, OVSDB_LOG_READ_ONLY, NULL, schemap);
+}
+
+/* Replica implementation. */
+
+struct ovsdb_file {
+    struct ovsdb_replica replica;
+    struct ovsdb *db;
+    struct ovsdb_log *log;
+    char *file_name;
+    long long int last_compact;
+    long long int next_compact;
+    unsigned int n_transactions;
+};
+
+static const struct ovsdb_replica_class ovsdb_file_class;
+
+static struct ovsdb_error *
+ovsdb_file_create(struct ovsdb *db, struct ovsdb_log *log,
+                  const char *file_name,
+                  unsigned int n_transactions,
+                  struct ovsdb_file **filep)
+{
+    struct ovsdb_file *file;
+    char *deref_name;
+    char *abs_name;
+
+    /* Use the absolute name of the file because ovsdb-server opens its
+     * database before daemonize() chdirs to "/". */
+    deref_name = follow_symlinks(file_name);
+    abs_name = abs_file_name(NULL, deref_name);
+    free(deref_name);
+    if (!abs_name) {
+        *filep = NULL;
+        return ovsdb_io_error(0, "could not determine current "
+                              "working directory");
     }
 
-    if (json->type == JSON_STRING) {
-        error = ovsdb_syntax_error(NULL, NULL, "%s: %lu bytes starting at "
-                                   "offset %lld are not valid JSON (%s)",
-                                   file->name, data_length,
-                                   (long long int) data_offset,
-                                   json->u.string);
-        goto error;
+    file = xmalloc(sizeof *file);
+    ovsdb_replica_init(&file->replica, &ovsdb_file_class);
+    file->db = db;
+    file->log = log;
+    file->file_name = abs_name;
+    file->last_compact = time_msec();
+    file->next_compact = file->last_compact + COMPACT_MIN_MSEC;
+    file->n_transactions = n_transactions;
+    ovsdb_add_replica(db, &file->replica);
+
+    *filep = file;
+    return NULL;
+}
+
+static struct ovsdb_file *
+ovsdb_file_cast(struct ovsdb_replica *replica)
+{
+    ovs_assert(replica->class == &ovsdb_file_class);
+    return CONTAINER_OF(replica, struct ovsdb_file, replica);
+}
+
+static bool
+ovsdb_file_change_cb(const struct ovsdb_row *old,
+                     const struct ovsdb_row *new,
+                     const unsigned long int *changed,
+                     void *ftxn_)
+{
+    struct ovsdb_file_txn *ftxn = ftxn_;
+    ovsdb_file_txn_add_row(ftxn, old, new, changed);
+    return true;
+}
+
+static struct ovsdb_error *
+ovsdb_file_commit(struct ovsdb_replica *replica,
+                  const struct ovsdb_txn *txn, bool durable)
+{
+    struct ovsdb_file *file = ovsdb_file_cast(replica);
+    struct ovsdb_file_txn ftxn;
+    struct ovsdb_error *error;
+
+    ovsdb_file_txn_init(&ftxn);
+    ovsdb_txn_for_each_change(txn, ovsdb_file_change_cb, &ftxn);
+    if (!ftxn.json) {
+        /* Nothing to commit. */
+        return NULL;
     }
 
-    file->offset = data_offset + data_length;
-    *jsonp = json;
-    return 0;
+    error = ovsdb_file_txn_commit(ftxn.json, ovsdb_txn_get_comment(txn),
+                                  durable, file->log);
+    if (error) {
+        return error;
+    }
+    file->n_transactions++;
+
+    /* If it has been at least COMPACT_MIN_MSEC ms since the last time we
+     * compacted (or at least COMPACT_RETRY_MSEC ms since the last time we
+     * tried), and if there are at least 100 transactions in the database, and
+     * if the database is at least 10 MB, then compact the database. */
+    if (time_msec() >= file->next_compact
+        && file->n_transactions >= 100
+        && ovsdb_log_get_offset(file->log) >= 10 * 1024 * 1024)
+    {
+        error = ovsdb_file_compact(file);
+        if (error) {
+            char *s = ovsdb_error_to_string(error);
+            ovsdb_error_destroy(error);
+            VLOG_WARN("%s: compacting database failed (%s), retrying in "
+                      "%d seconds",
+                      file->file_name, s, COMPACT_RETRY_MSEC / 1000);
+            free(s);
+
+            file->next_compact = time_msec() + COMPACT_RETRY_MSEC;
+        }
+    }
 
-error:
-    file->read_error = ovsdb_error_clone(error);
-    json_destroy(json);
-    return error;
+    return NULL;
 }
 
 struct ovsdb_error *
-ovsdb_file_write(struct ovsdb_file *file, struct json *json)
+ovsdb_file_compact(struct ovsdb_file *file)
 {
-    uint8_t sha1[SHA1_DIGEST_SIZE];
+    struct ovsdb_log *new_log = NULL;
+    struct lockfile *tmp_lock = NULL;
     struct ovsdb_error *error;
-    char *json_string;
-    char header[128];
-    size_t length;
-
-    json_string = NULL;
-
-    if (file->write_error) {
-        return ovsdb_error_clone(file->write_error);
-    } else if (file->mode == OVSDB_FILE_READ) {
-        file->mode = OVSDB_FILE_WRITE;
-        if (fseeko(file->stream, file->offset, SEEK_SET)) {
-            error = ovsdb_io_error(errno, "%s: cannot seek to offset %lld",
-                                   file->name, (long long int) file->offset);
-            goto error;
-        }
-        if (ftruncate(fileno(file->stream), file->offset)) {
-            error = ovsdb_io_error(errno, "%s: cannot truncate to length %lld",
-                                   file->name, (long long int) file->offset);
-            goto error;
-        }
+    char *tmp_name = NULL;
+    char *comment = NULL;
+    int retval;
+
+    comment = xasprintf("compacting database online "
+                        "(%.3f seconds old, %u transactions, %llu bytes)",
+                        (time_wall_msec() - file->last_compact) / 1000.0,
+                        file->n_transactions,
+                        (unsigned long long) ovsdb_log_get_offset(file->log));
+    VLOG_INFO("%s: %s", file->file_name, comment);
+
+    /* Commit the old version, so that we can be assured that we'll eventually
+     * have either the old or the new version. */
+    error = ovsdb_log_commit(file->log);
+    if (error) {
+        goto exit;
     }
 
-    if (json->type != JSON_OBJECT && json->type != JSON_ARRAY) {
-        error = OVSDB_BUG("bad JSON type");
-        goto error;
+    /* Lock temporary file. */
+    tmp_name = xasprintf("%s.tmp", file->file_name);
+    retval = lockfile_lock(tmp_name, &tmp_lock);
+    if (retval) {
+        error = ovsdb_io_error(retval, "could not get lock on %s", tmp_name);
+        goto exit;
     }
 
-    /* Compose content.  Add a new-line (replacing the null terminator) to make
-     * the file easier to read, even though it has no semantic value.  */
-    json_string = json_to_string(json, 0);
-    length = strlen(json_string) + 1;
-    json_string[length - 1] = '\n';
+    /* Remove temporary file.  (It might not exist.) */
+    if (unlink(tmp_name) < 0 && errno != ENOENT) {
+        error = ovsdb_io_error(errno, "failed to remove %s", tmp_name);
+        goto exit;
+    }
 
-    /* Compose header. */
-    sha1_bytes(json_string, length, sha1);
-    snprintf(header, sizeof header, "%s%zu "SHA1_FMT"\n",
-             magic, length, SHA1_ARGS(sha1));
+    /* Save a copy. */
+    error = ovsdb_file_save_copy__(tmp_name, false, comment, file->db,
+                                   &new_log);
+    if (error) {
+        goto exit;
+    }
 
-    /* Write. */
-    if (fwrite(header, strlen(header), 1, file->stream) != 1
-        || fwrite(json_string, length, 1, file->stream) != 1
-        || fflush(file->stream))
-    {
-        error = ovsdb_io_error(errno, "%s: write failed", file->name);
+    /* Replace original by temporary. */
+    if (rename(tmp_name, file->file_name)) {
+        error = ovsdb_io_error(errno, "failed to rename \"%s\" to \"%s\"",
+                               tmp_name, file->file_name);
+        goto exit;
+    }
+    fsync_parent_dir(file->file_name);
+
+exit:
+    if (!error) {
+        ovsdb_log_close(file->log);
+        file->log = new_log;
+        file->last_compact = time_msec();
+        file->next_compact = file->last_compact + COMPACT_MIN_MSEC;
+        file->n_transactions = 1;
+    } else {
+        ovsdb_log_close(new_log);
+        if (tmp_lock) {
+            unlink(tmp_name);
+        }
+    }
 
-        /* Remove any partially written data, ignoring errors since there is
-         * nothing further we can do. */
-        ftruncate(fileno(file->stream), file->offset);
+    lockfile_unlock(tmp_lock);
+    free(tmp_name);
+    free(comment);
 
-        goto error;
+    return error;
+}
+
+static void
+ovsdb_file_destroy(struct ovsdb_replica *replica)
+{
+    struct ovsdb_file *file = ovsdb_file_cast(replica);
+
+    ovsdb_log_close(file->log);
+    free(file->file_name);
+    free(file);
+}
+
+static const struct ovsdb_replica_class ovsdb_file_class = {
+    ovsdb_file_commit,
+    ovsdb_file_destroy
+};
+
+static void
+ovsdb_file_txn_init(struct ovsdb_file_txn *ftxn)
+{
+    ftxn->json = NULL;
+    ftxn->table_json = NULL;
+    ftxn->table = NULL;
+}
+
+static void
+ovsdb_file_txn_add_row(struct ovsdb_file_txn *ftxn,
+                       const struct ovsdb_row *old,
+                       const struct ovsdb_row *new,
+                       const unsigned long int *changed)
+{
+    struct json *row;
+
+    if (!new) {
+        row = json_null_create();
+    } else {
+        struct shash_node *node;
+
+        row = old ? NULL : json_object_create();
+        SHASH_FOR_EACH (node, &new->table->schema->columns) {
+            const struct ovsdb_column *column = node->data;
+            const struct ovsdb_type *type = &column->type;
+            unsigned int idx = column->index;
+
+            if (idx != OVSDB_COL_UUID && column->persistent
+                && (old
+                    ? bitmap_is_set(changed, idx)
+                    : !ovsdb_datum_is_default(&new->fields[idx], type)))
+            {
+                if (!row) {
+                    row = json_object_create();
+                }
+                json_object_put(row, column->name,
+                                ovsdb_datum_to_json(&new->fields[idx], type));
+            }
+        }
     }
 
-    file->offset += strlen(header) + length;
-    free(json_string);
-    return 0;
+    if (row) {
+        struct ovsdb_table *table = new ? new->table : old->table;
+        char uuid[UUID_LEN + 1];
 
-error:
-    file->write_error = ovsdb_error_clone(error);
-    free(json_string);
-    return error;
+        if (table != ftxn->table) {
+            /* Create JSON object for transaction overall. */
+            if (!ftxn->json) {
+                ftxn->json = json_object_create();
+            }
+
+            /* Create JSON object for transaction on this table. */
+            ftxn->table_json = json_object_create();
+            ftxn->table = table;
+            json_object_put(ftxn->json, table->schema->name, ftxn->table_json);
+        }
+
+        /* Add row to transaction for this table. */
+        snprintf(uuid, sizeof uuid,
+                 UUID_FMT, UUID_ARGS(ovsdb_row_get_uuid(new ? new : old)));
+        json_object_put(ftxn->table_json, uuid, row);
+    }
 }
 
-struct ovsdb_error *
-ovsdb_file_commit(struct ovsdb_file *file)
+static struct ovsdb_error *
+ovsdb_file_txn_commit(struct json *json, const char *comment,
+                      bool durable, struct ovsdb_log *log)
 {
-    if (fsync(fileno(file->stream))) {
-        return ovsdb_io_error(errno, "%s: fsync failed", file->name);
+    struct ovsdb_error *error;
+
+    if (!json) {
+        json = json_object_create();
+    }
+    if (comment) {
+        json_object_put_string(json, "_comment", comment);
+    }
+    json_object_put(json, "_date", json_integer_create(time_wall_msec()));
+
+    error = ovsdb_log_write(log, json);
+    json_destroy(json);
+    if (error) {
+        return ovsdb_wrap_error(error, "writing transaction failed");
     }
-    return 0;
+
+    if (durable) {
+        error = ovsdb_log_commit(log);
+        if (error) {
+            return ovsdb_wrap_error(error, "committing transaction failed");
+        }
+    }
+
+    return NULL;
 }