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@ -140,7 +140,7 @@ static int mqtt3_db_message_store_write(struct mosquitto_db *db, FILE *db_fptr)
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stored = db->msg_store;
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while(stored){
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if(stored->topic && !strncmp(stored->topic, "$SYS", 4)){
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if(stored->ref_count == 1 && stored->dest_id_count == 0){
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if(stored->ref_count <= 1 && stored->dest_id_count == 0){
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/* $SYS messages that are only retained shouldn't be persisted. */
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stored = stored->next;
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continue;
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@ -261,6 +261,7 @@ static int _db_subs_retain_write(struct mosquitto_db *db, FILE *db_fptr, struct
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char *thistopic;
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uint32_t length;
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uint16_t i16temp;
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uint8_t i8temp;
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dbid_t i64temp;
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size_t slen;
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@ -292,7 +293,8 @@ static int _db_subs_retain_write(struct mosquitto_db *db, FILE *db_fptr, struct
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write_e(db_fptr, &i16temp, sizeof(uint16_t));
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write_e(db_fptr, thistopic, slen);
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write_e(db_fptr, &sub->qos, sizeof(uint8_t));
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i8temp = (uint8_t )sub->qos;
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write_e(db_fptr, &i8temp, sizeof(uint8_t));
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}
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sub = sub->next;
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}
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@ -362,6 +364,36 @@ int mqtt3_db_backup(struct mosquitto_db *db, bool shutdown)
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}
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snprintf(outfile, len, "%s.new", db->config->persistence_filepath);
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outfile[len] = '\0';
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#ifndef WIN32
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/**
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*
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* If a system lost power during the rename operation at the
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* end of this file the filesystem could potentially be left
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* with a directory that looks like this after powerup:
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*
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* 24094 -rw-r--r-- 2 root root 4099 May 30 16:27 mosquitto.db
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* 24094 -rw-r--r-- 2 root root 4099 May 30 16:27 mosquitto.db.new
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*
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* The 24094 shows that mosquitto.db.new is hard-linked to the
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* same file as mosquitto.db. If fopen(outfile, "wb") is naively
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* called then mosquitto.db will be truncated and the database
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* potentially corrupted.
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*
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* Any existing mosquitto.db.new file must be removed prior to
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* opening to guarantee that it is not hard-linked to
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* mosquitto.db.
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*
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*/
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rc = unlink(outfile);
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if (rc != 0) {
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if (errno != ENOENT) {
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_mosquitto_log_printf(NULL, MOSQ_LOG_INFO, "Error saving in-memory database, unable to remove %s.", outfile);
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goto error;
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}
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}
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#endif
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db_fptr = _mosquitto_fopen(outfile, "wb");
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if(db_fptr == NULL){
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_mosquitto_log_printf(NULL, MOSQ_LOG_INFO, "Error saving in-memory database, unable to open %s for writing.", outfile);
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@ -395,6 +427,32 @@ int mqtt3_db_backup(struct mosquitto_db *db, bool shutdown)
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mqtt3_db_client_write(db, db_fptr);
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mqtt3_db_subs_retain_write(db, db_fptr);
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#ifndef WIN32
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/**
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*
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* Closing a file does not guarantee that the contents are
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* written to disk. Need to flush to send data from app to OS
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* buffers, then fsync to deliver data from OS buffers to disk
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* (as well as disk hardware permits).
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*
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* man close (http://linux.die.net/man/2/close, 2016-06-20):
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*
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* "successful close does not guarantee that the data has
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* been successfully saved to disk, as the kernel defers
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* writes. It is not common for a filesystem to flush
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* the buffers when the stream is closed. If you need
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* to be sure that the data is physically stored, use
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* fsync(2). (It will depend on the disk hardware at this
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* point."
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*
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* This guarantees that the new state file will not overwrite
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* the old state file before its contents are valid.
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*
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*/
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fflush(db_fptr);
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fsync(fileno(db_fptr));
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#endif
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fclose(db_fptr);
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#ifdef WIN32
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Roger A. Light
9 years ago