From cb9a84154c755daf0c9361346302ad41a1804ecc Mon Sep 17 00:00:00 2001

From: Peter Xu <peterx@redhat.com>

Date: Thu, 8 Nov 2018 06:29:32 +0000

Subject: [PATCH 04/35] qemu-error: introduce {error|warn}_report_once

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RH-Author: Peter Xu <peterx@redhat.com>

Message-id: <20181108062938.21143-2-peterx@redhat.com>

Patchwork-id: 82959

O-Subject: [RHEL-8 qemu-kvm PATCH 1/7] qemu-error: introduce {error|warn}_report_once

Bugzilla: 1625173

RH-Acked-by: Auger Eric <eric.auger@redhat.com>

RH-Acked-by: Michael S. Tsirkin <mst@redhat.com>

RH-Acked-by: Philippe Mathieu-Daudé <philmd@redhat.com>

RH-Acked-by: Laurent Vivier <lvivier@redhat.com>

Bugzilla: 1625173

There are many error_report()s that can be used in frequently called

functions, especially on IO paths.  That can be unideal in that

malicious guest can try to trigger the error tons of time which might

use up the log space on the host (e.g., libvirt can capture the stderr

of QEMU and put it persistently onto disk).  In VT-d emulation code, we

have trace_vtd_error() tracer.  AFAIU all those places can be replaced

by something like error_report() but trace points are mostly used to

avoid the DDOS attack that mentioned above.  However using trace points

mean that errors are not dumped if trace not enabled.

It's not a big deal in most modern server managements since we have

things like logrotate to maintain the logs and make sure the quota is

expected.  However it'll still be nice that we just provide another way

to restrict message generations.  In most cases, this kind of

error_report()s will only provide valid information on the first message

sent, and all the rest of similar messages will be mostly talking about

the same thing.  This patch introduces *_report_once() helpers to allow

a message to be dumped only once during one QEMU process's life cycle.

It will make sure: (1) it's on by deffault, so we can even get something

without turning the trace on and reproducing, and (2) it won't be

affected by DDOS attack.

To implement it, I stole the printk_once() macro from Linux.

CC: Eric Blake <eblake@redhat.com>

CC: Markus Armbruster <armbru@redhat.com>

Signed-off-by: Peter Xu <peterx@redhat.com>

Message-Id: <20180815095328.32414-2-peterx@redhat.com>

Reviewed-by: Markus Armbruster <armbru@redhat.com>

[Whitespace adjusted, comments improved]

Signed-off-by: Markus Armbruster <armbru@redhat.com>

(cherry picked from commit bc6a69dd4bfa41ae56235dcbb9a28a56e12a7dc6)

Signed-off-by: Peter Xu <peterx@redhat.com>

Signed-off-by: Danilo C. L. de Paula <ddepaula@redhat.com>

---

 include/qemu/error-report.h | 32 ++++++++++++++++++++++++++++++++

 1 file changed, 32 insertions(+)

diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h

index e1c8ae1..72fab2b 100644

--- a/include/qemu/error-report.h

+++ b/include/qemu/error-report.h

@@ -44,6 +44,38 @@ void error_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);

 void warn_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);

 void info_report(const char *fmt, ...) GCC_FMT_ATTR(1, 2);

+/*

+ * Similar to error_report(), except it prints the message just once.

+ * Return true when it prints, false otherwise.

+ */

+#define error_report_once(fmt, ...)             \

+    ({                                          \

+        static bool print_once_;                \

+        bool ret_print_once_ = !print_once_;    \

+                                                \

+        if (!print_once_) {                     \

+            print_once_ = true;                 \

+            error_report(fmt, ##__VA_ARGS__);   \

+        }                                       \

+        unlikely(ret_print_once_);              \

+    })

+

+/*

+ * Similar to warn_report(), except it prints the message just once.

+ * Return true when it prints, false otherwise.

+ */

+#define warn_report_once(fmt, ...)              \

+    ({                                          \

+        static bool print_once_;                \

+        bool ret_print_once_ = !print_once_;    \

+                                                \

+        if (!print_once_) {                     \

+            print_once_ = true;                 \

+            warn_report(fmt, ##__VA_ARGS__);    \

+        }                                       \

+        unlikely(ret_print_once_);              \

+    })

+

 const char *error_get_progname(void);

 extern bool enable_timestamp_msg;

-- 

1.8.3.1