PATCH: improve robustness of xenconsoled logfile handling

PATCH: improve robustness of xenconsoled logfile handling

[Daniel P. Berrange]

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Attached is an small patch to xenconsoled to make the persistent logging
code I previously added a little more robust. First change is to check 
the 'log_reload' on every iteration of the select() loop, not just when
select() returns EINTR. This is because the log reload signal may have
iterrupted a syscall other than select & thus without this change  we
might miss the reload signal.  The second change makes us process the
hypervisor logs on every iteration of the loop, not just upon timeouts.
This is because if a guest VM were consistently sending some log message
and < 1 second period, the select() would never hit the 1 second timeout
and thus never process the HV logs. 

Thanks to Markus Armbruster for pointing out both these edge cases

   Signed-off-by: Daniel P. Berrange <berrange@redhat.com>


 io.c |   30 +++++++++++++++++++-----------
 1 file changed, 19 insertions(+), 11 deletions(-)


Regards,
Dan.
-- 
|=- Red Hat, Engineering, Emerging Technologies, Boston.  +1 978 392 2496 -=|
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diff -r 9261686d840c tools/console/daemon/io.c
--- a/tools/console/daemon/io.c	Tue Jun 26 12:40:37 2007 +0100
+++ b/tools/console/daemon/io.c	Tue Jun 26 15:36:36 2007 -0400
@@ -766,23 +766,27 @@ void handle_io(void)
 		 * for new HV log data as we can with guest */
 		ret = select(max_fd + 1, &readfds, &writefds, 0, log_hv_fd != -1 ? &timeout : NULL);
 
+		if (log_reload) {
+			handle_log_reload();
+			log_reload = 0;
+		}
+
+		/* Abort if select failed, except for EINTR cases
+		   which indicate a possible log reload */
 		if (ret == -1) {
-			if (errno == EINTR) {
-				if (log_reload) {
-					handle_log_reload();
-					log_reload = 0;
-				}
+			if (errno == EINTR)
 				continue;
-			}
 			dolog(LOG_ERR, "Failure in select: %d (%s)",
 			      errno, strerror(errno));
 			break;
 		}
 
-		/* Check for timeout */
+		/* Always process HV logs even if not a timeout */
+		if (log_hv_fd != -1)
+			handle_hv_logs();
+
+		/* Must not check returned FDSET if it was a timeout */
 		if (ret == 0) {
-			if (log_hv_fd != -1)
-				handle_hv_logs();
 			continue;
 		}
 
@@ -806,10 +810,14 @@ void handle_io(void)
 		}
 	}
 
-	if (log_hv_fd != -1)
+	if (log_hv_fd != -1) {
 		close(log_hv_fd);
-	if (xc_handle != -1)
+		log_hv_fd = -1;
+	}
+	if (xc_handle != -1) {
 		xc_interface_close(xc_handle);
+		xc_handle = -1;
+	}
 }
 
 /*

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