Re: [Libguestfs] [nbdkit PATCH 2/2] filters: Add log filter

'nbdkit -v' is quite verbose, and traces everything. Sometimes, we want to trace JUST the client interactions. In particular, when debugging another filter, being able to trace what the filter called can be quite useful; and having the log filter in place will make it easier to add testsuite coverage of other filters. Also, it is nice to have timestamps in the log, in order to see if message interleaving takes place, and what delays are occurring. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; ---

+=head1 PARAMETERS + +The nbdkit-log-filter accepts a single parameter C<logfile> which +specifies the path of the file to use for logging. If the file +already exists, it will be truncated. If C<logfile> is omitted, +logging is send to stderr.

+++ b/filters/log/log.c

+static void +log_unload (void) +{ + if (logfilename) + fclose (logfile); + free (logfilename); +}

+/* Output a timestamp and the log message. */ +static void __attribute__ ((format (printf, 4, 5))) +output (struct handle *h, const char *act, uint64_t id, const char *fmt, ...) +{ + va_list args; + struct timeval tv; + struct tm tm; + char timestamp[27] = "Time unknown"; + + /* Logging is best effort, so ignore failure to get timestamp */ + if (!gettimeofday (&tv, NULL)) + { + size_t s; + + gmtime_r (&tv.tv_sec, &tm); + s = strftime (timestamp, sizeof timestamp, "%F %T", &tm); + assert (s); + s = snprintf (timestamp + s, sizeof timestamp - s, ".%06ld", + 0L + tv.tv_usec); + } + flockfile (logfile); + fprintf (logfile, "%s connection=%" PRIu64 " %s ", timestamp, h->connection, + act); + if (id) + fprintf (logfile, "id=%" PRIu64 " ", id); + va_start (args, fmt); + vfprintf (logfile, fmt, args); + va_end (args); + fputc ('\n', logfile); + funlockfile (logfile);