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Re: [Qemu-devel] [PATCH v5 1/3] qemu-error: introduce {error|warn}_repor
From: |
Markus Armbruster |
Subject: |
Re: [Qemu-devel] [PATCH v5 1/3] qemu-error: introduce {error|warn}_report_once |
Date: |
Wed, 15 Aug 2018 13:36:52 +0200 |
User-agent: |
Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux) |
Peter Xu <address@hidden> writes:
> 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 <address@hidden>
> CC: Markus Armbruster <address@hidden>
> Signed-off-by: Peter Xu <address@hidden>
> ---
> 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 e1c8ae1a52..c7ec54cb97 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(), but it only prints the message once. It
> + * returns true when it prints the first time, otherwise false.
> + */
> +#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(), but it only prints the message once. It
> + * returns true when it prints the first time, otherwise false.
> + */
> +#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;
With the touch-ups from my review of v4 squashed in (fixup patch
appended):
Reviewed-by: Markus Armbruster <address@hidden>
>From f57a2317c75bea5396a589b2d65933312850bb05 Mon Sep 17 00:00:00 2001
From: Markus Armbruster <address@hidden>
Date: Wed, 15 Aug 2018 13:29:03 +0200
Subject: [PATCH] fixup! intel-iommu: start to use error_report_once
[Whitespace adjusted, comments improved]
---
include/qemu/error-report.h | 30 +++++++++++++++---------------
1 file changed, 15 insertions(+), 15 deletions(-)
diff --git a/include/qemu/error-report.h b/include/qemu/error-report.h
index c7ec54cb97..72fab2b031 100644
--- a/include/qemu/error-report.h
+++ b/include/qemu/error-report.h
@@ -45,35 +45,35 @@ 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(), but it only prints the message once. It
- * returns true when it prints the first time, otherwise false.
+ * 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_; \
+ static bool print_once_; \
+ bool ret_print_once_ = !print_once_; \
\
- if (!print_once_) { \
- print_once_ = true; \
+ if (!print_once_) { \
+ print_once_ = true; \
error_report(fmt, ##__VA_ARGS__); \
} \
- unlikely(ret_print_once_); \
+ unlikely(ret_print_once_); \
})
/*
- * Similar to warn_report(), but it only prints the message once. It
- * returns true when it prints the first time, otherwise false.
+ * 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_; \
+ static bool print_once_; \
+ bool ret_print_once_ = !print_once_; \
\
- if (!print_once_) { \
- print_once_ = true; \
- warn_report(fmt, ##__VA_ARGS__); \
+ if (!print_once_) { \
+ print_once_ = true; \
+ warn_report(fmt, ##__VA_ARGS__); \
} \
- unlikely(ret_print_once_); \
+ unlikely(ret_print_once_); \
})
const char *error_get_progname(void);
--
2.17.1