[Xen-changelog] [xen-unstable] xenconsoled: improve robustness of logfile handling

[Xen patchbot-unstable <patchbot-unstable@xxxxxxxxxxxxxxxxxxx>]

# HG changeset patch
# User Keir Fraser <keir@xxxxxxxxxxxxx>
# Date 1182974754 -3600
# Node ID f152e44325a7eab2bf6e0994c4ef5fca12d93d52
# Parent  4ab9e4bbd61b4748ccc76566af88d98cd4e7bbb1
xenconsoled: improve robustness of logfile handling

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@xxxxxxxxxx>
---
 tools/console/daemon/io.c |   38 +++++++++++++++++++++++---------------
 1 files changed, 23 insertions(+), 15 deletions(-)

diff -r 4ab9e4bbd61b -r f152e44325a7 tools/console/daemon/io.c
--- a/tools/console/daemon/io.c Wed Jun 27 21:01:08 2007 +0100
+++ b/tools/console/daemon/io.c Wed Jun 27 21:05:54 2007 +0100
@@ -764,27 +764,31 @@ void handle_io(void)
                /* XXX I wish we didn't have to busy wait for hypervisor logs
                 * but there's no obvious way to get event channel notifications
                 * for new HV log data as we can with guest */
-               ret = select(max_fd + 1, &readfds, &writefds, 0, log_hv_fd != 
-1 ? &timeout : NULL);
-
+               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 */
-               if (ret == 0) {
-                       if (log_hv_fd != -1)
-                               handle_hv_logs();
+               /* 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)
                        continue;
-               }
 
                if (FD_ISSET(xs_fileno(xs), &readfds))
                        handle_xs();
@@ -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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