tools: hv: Enable debug logs for hv_kvp_daemon

Allow the KVP daemon to log the KVP updates triggered in the VM
with a new debug flag(-d).
When the daemon is started with this flag, it logs updates and debug
information in syslog with loglevel LOG_DEBUG. This information comes
in handy for debugging issues where the key-value pairs for certain
pools show mismatch/incorrect values.
The distro-vendors can further consume these changes and modify the
respective service files to redirect the logs to specific files as
needed.

Signed-off-by: Shradha Gupta <[e-mail]>
Reviewed-by: Naman Jain <[e-mail]>
Reviewed-by: Dexuan Cui <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Wei Liu <[e-mail]>
Message-ID: <[e-mail]>

tools/hv/hv_kvp_daemon.c

···
 };
 
 static int in_hand_shake;
+static int debug;
 
 static char *os_name = "";
 static char *os_major = "";
···
 	kvp_release_lock(pool);
 }
 
+static void kvp_dump_initial_pools(int pool)
+{
+	int i;
+
+	syslog(LOG_DEBUG, "===Start dumping the contents of pool %d ===\n",
+	       pool);
+
+	for (i = 0; i < kvp_file_info[pool].num_records; i++)
+		syslog(LOG_DEBUG, "pool: %d, %d/%d key=%s val=%s\n",
+		       pool, i + 1, kvp_file_info[pool].num_records,
+		       kvp_file_info[pool].records[i].key,
+		       kvp_file_info[pool].records[i].value);
+}
+
 static void kvp_update_mem_state(int pool)
 {
 	FILE *filep;
···
 			return 1;
 		kvp_file_info[i].num_records = 0;
 		kvp_update_mem_state(i);
+		if (debug)
+			kvp_dump_initial_pools(i);
 	}
 
 	return 0;
···
 		 * Found a match; just move the remaining
 		 * entries up.
 		 */
+		if (debug)
+			syslog(LOG_DEBUG, "%s: deleting the KVP: pool=%d key=%s val=%s",
+			       __func__, pool, record[i].key, record[i].value);
 		if (i == (num_records - 1)) {
 			kvp_file_info[pool].num_records--;
 			kvp_update_file(pool);
···
 		kvp_update_file(pool);
 		return 0;
 	}
+
+	if (debug)
+		syslog(LOG_DEBUG, "%s: could not delete KVP: pool=%d key=%s. Record not found",
+		       __func__, pool, key);
+
 	return 1;
 }
 
 static int kvp_key_add_or_modify(int pool, const __u8 *key, int key_size,
 				 const __u8 *value, int value_size)
 {
-	int i;
-	int num_records;
 	struct kvp_record *record;
+	int num_records;
 	int num_blocks;
+	int i;
+
+	if (debug)
+		syslog(LOG_DEBUG, "%s: got a KVP: pool=%d key=%s val=%s",
+		       __func__, pool, key, value);
 
 	if ((key_size > HV_KVP_EXCHANGE_MAX_KEY_SIZE) ||
-		(value_size > HV_KVP_EXCHANGE_MAX_VALUE_SIZE))
+		(value_size > HV_KVP_EXCHANGE_MAX_VALUE_SIZE)) {
+		syslog(LOG_ERR, "%s: Too long key or value: key=%s, val=%s",
+		       __func__, key, value);
+
+		if (debug)
+			syslog(LOG_DEBUG, "%s: Too long key or value: pool=%d, key=%s, val=%s",
+			       __func__, pool, key, value);
 		return 1;
+	}
 
 	/*
 	 * First update the in-memory state.
···
 		 */
 		memcpy(record[i].value, value, value_size);
 		kvp_update_file(pool);
+		if (debug)
+			syslog(LOG_DEBUG, "%s: updated: pool=%d key=%s val=%s",
+			       __func__, pool, key, value);
 		return 0;
 	}
 
···
 		record = realloc(record, sizeof(struct kvp_record) *
 			 ENTRIES_PER_BLOCK * (num_blocks + 1));
 
-		if (record == NULL)
+		if (!record) {
+			syslog(LOG_ERR, "%s: Memory alloc failure", __func__);
 			return 1;
+		}
 		kvp_file_info[pool].num_blocks++;
 
 	}
···
 	memcpy(record[i].key, key, key_size);
 	kvp_file_info[pool].records = record;
 	kvp_file_info[pool].num_records++;
+
+	if (debug)
+		syslog(LOG_DEBUG, "%s: added: pool=%d key=%s val=%s",
+		       __func__, pool, key, value);
+
 	kvp_update_file(pool);
 	return 0;
 }
···
 	fprintf(stderr, "Usage: %s [options]\n"
 		"Options are:\n"
 		"  -n, --no-daemon        stay in foreground, don't daemonize\n"
+		"  -d, --debug            Enable debug logs(syslog debug by default)\n"
 		"  -h, --help             print this help\n", argv[0]);
 }
 
···
 	static struct option long_options[] = {
 		{"help",	no_argument,	   0,  'h' },
 		{"no-daemon",	no_argument,	   0,  'n' },
+		{"debug",	no_argument,	   0,  'd' },
 		{0,		0,		   0,  0   }
 	};
 
-	while ((opt = getopt_long(argc, argv, "hn", long_options,
+	while ((opt = getopt_long(argc, argv, "hnd", long_options,
 				  &long_index)) != -1) {
 		switch (opt) {
 		case 'n':
···
 		case 'h':
 			print_usage(argv);
 			exit(0);
+		case 'd':
+			debug = 1;
+			break;
 		default:
 			print_usage(argv);
 			exit(EXIT_FAILURE);
···
 	 * unpredictable amount of time to finish.
 	 */
 	kvp_get_domain_name(full_domain_name, sizeof(full_domain_name));
+
+	if (debug)
+		syslog(LOG_INFO, "Logging debug info in syslog(debug)");
 
 	if (kvp_file_init()) {
 		syslog(LOG_ERR, "Failed to initialize the pools");