Add syslog and fatal signal handler feature

I see random ENOTCONN failures in xfstest generic/013 and generic/014
in my branch, but earliest on the 2nd run - takes ~12hours to get
the issue, but then there are no further information logged.
ENOTCONN points to a daemon crash - I need backtraces and a core dump.

This adds optional handling of fatal signals to print a core dump
and optional syslog logging with these new public functions:

fuse_set_fail_signal_handlers()
    In addition to the existing fuse_set_signal_handlers(). This is not
    enabled together with fuse_set_signal_handlers(), as it is change
    in behavior and file systems might already have their own fatal
    handlers.

fuse_log_enable_syslog
    Print logs to syslog instead of stderr

fuse_log_close_syslog
    Close syslog (for now just does closelog())

Code in fuse_signals.c is also updated, to be an array of signals,
and setting signal handlers is now down with a for-loop instead
of one hand coded set_one_signal_handler() per signal.

2 files changed, 29 insertions, 0 deletions

diff --git a/include/fuse_common.h b/include/fuse_common.h
index 04ecb95..6de2640 100644
--- a/include/fuse_common.h
+++ b/include/fuse_common.h
@@ -955,6 +955,23 @@ ssize_t fuse_buf_copy(struct fuse_bufvec *dst, struct fuse_bufvec *src,
 int fuse_set_signal_handlers(struct fuse_session *se);
 
 /**
+ * Print a stack backtrace diagnostic on critical signals ()
+ *
+ * Stores session in a global variable.	 May only be called once per
+ * process until fuse_remove_signal_handlers() is called.
+ *
+ * Once either of the POSIX signals arrives, the signal handler calls
+ * fuse_session_exit().
+ *
+ * @param se the session to exit
+ * @return 0 on success, -1 on failure
+ *
+ * See also:
+ * fuse_remove_signal_handlers()
+ */
+int fuse_set_fail_signal_handlers(struct fuse_session *se);
+
+/**
  * Restore default signal handlers
  *
  * Resets global session.  After this fuse_set_signal_handlers() may
diff --git a/include/fuse_log.h b/include/fuse_log.h
index 5e112e0..c855957 100644
--- a/include/fuse_log.h
+++ b/include/fuse_log.h
@@ -75,6 +75,18 @@ void fuse_set_log_func(fuse_log_func_t func);
  */
 void fuse_log(enum fuse_log_level level, const char *fmt, ...);
 
+/**
+ * Switch default log handler from stderr to syslog
+ *
+ * Passed options are according to 'man 3 openlog'
+ */
+void fuse_log_enable_syslog(const char *ident, int option, int facility);
+
+/**
+ * To be called at teardown to close syslog.
+*/
+void fuse_log_close_syslog(void);
+
 #ifdef __cplusplus
 }
 #endif