log, conf: Add support for logging to file

In some environments, such as KubeVirt pods, we might not have a
system logger available. We could choose to run in foreground, but
this takes away the convenient synchronisation mechanism derived from
forking to background when interfaces are ready.

Add optional logging to file with -l/--log-file and --log-size.

Unfortunately, this means we need to duplicate features that are more
appropriately implemented by a system logger, such as rotation. Keep
that reasonably simple, by using fallocate() with range collapsing
where supported (Linux kernel >= 3.15, extent-based ext4 and XFS) and
falling back to an unsophisticated block-by-block moving of entries
toward the beginning of the file once we reach the (mandatory) size
limit.

While at it, clarify the role of LOG_EMERG in passt.c.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>

1 files changed, 6 insertions, 0 deletions

diff --git a/log.h b/log.h
index 70cad6f..f92394c 100644
--- a/log.h
+++ b/log.h
@@ -6,6 +6,10 @@
 #ifndef LOG_H
 #define LOG_H
 
+#define LOGFILE_SIZE_DEFAULT		(1024 * 1024UL)
+#define LOGFILE_CUT_RATIO		30	/* When full, cut ~30% size */
+#define LOGFILE_SIZE_MIN		(5UL * MAX(BUFSIZ, PAGE_SIZE))
+
 void err(const char *format, ...);
 void warn(const char *format, ...);
 void info(const char *format, ...);
@@ -20,7 +24,9 @@ void trace_init(int enable);
 	} while (0)
 
 void __openlog(const char *ident, int option, int facility);
+void logfile_init(const char *name, const char *path, size_t size);
 void passt_vsyslog(int pri, const char *format, va_list ap);
+void logfile_write(int pri, const char *format, va_list ap);
 void __setlogmask(int mask);
 
 #endif /* LOG_H */