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Re: [PATCH v2 3/6] Add a mutex to guarantee single writer to qemu_logfil
From: |
Alex Bennée |
Subject: |
Re: [PATCH v2 3/6] Add a mutex to guarantee single writer to qemu_logfile handle. |
Date: |
Mon, 18 Nov 2019 12:16:32 +0000 |
User-agent: |
mu4e 1.3.5; emacs 27.0.50 |
Robert Foley <address@hidden> writes:
> Also added qemu_logfile_init() for initializing the logfile mutex.
>
> Signed-off-by: Robert Foley <address@hidden>
> ---
> v2
> - In qemu_set_log() moved location of mutex lock/unlock
> due to cleanup changes.
> ---
> v1
> - changed qemu_logfile_init() to use __constructor__.
> ---
> util/log.c | 14 ++++++++++++++
> 1 file changed, 14 insertions(+)
>
> diff --git a/util/log.c b/util/log.c
> index 417d16ec66..91ebb5c924 100644
> --- a/util/log.c
> +++ b/util/log.c
> @@ -24,8 +24,10 @@
> #include "qapi/error.h"
> #include "qemu/cutils.h"
> #include "trace/control.h"
> +#include "qemu/thread.h"
>
> static char *logfilename;
> +static QemuMutex qemu_logfile_mutex;
> FILE *qemu_logfile;
> int qemu_loglevel;
> static int log_append = 0;
> @@ -49,6 +51,11 @@ int qemu_log(const char *fmt, ...)
> return ret;
> }
>
> +static void __attribute__((__constructor__)) qemu_logfile_init(void)
> +{
> + qemu_mutex_init(&qemu_logfile_mutex);
> +}
> +
> static bool log_uses_own_buffers;
>
> /* enable or disable low levels log */
> @@ -70,7 +77,10 @@ void qemu_set_log(int log_flags)
> if (qemu_loglevel && (!is_daemonized() || logfilename)) {
> need_to_open_file = true;
> }
> + g_assert(qemu_logfile_mutex.initialized);
> + qemu_mutex_lock(&qemu_logfile_mutex);
> if (qemu_logfile && !need_to_open_file) {
> + qemu_mutex_unlock(&qemu_logfile_mutex);
> qemu_log_close();
> } else if (!qemu_logfile && need_to_open_file) {
> if (logfilename) {
> @@ -105,6 +115,7 @@ void qemu_set_log(int log_flags)
> #endif
> log_append = 1;
> }
> + qemu_mutex_unlock(&qemu_logfile_mutex);
> }
> }
This looks a bit odd. I can see it's fixed up in a later patch but I
guess the reason is to avoid a double lock when we get to
qemu_log_close(). In the cases of unavoidable temporary ugliness in a
patch series it is best to note the problem and mention it will be
cleaned up by a later patch in the series.
With an extra comment in the commit message:
Reviewed-by: Alex Bennée <address@hidden>
>
> @@ -240,12 +251,15 @@ void qemu_log_flush(void)
> /* Close the log file */
> void qemu_log_close(void)
> {
> + g_assert(qemu_logfile_mutex.initialized);
> + qemu_mutex_lock(&qemu_logfile_mutex);
> if (qemu_logfile) {
> if (qemu_logfile != stderr) {
> fclose(qemu_logfile);
> }
> qemu_logfile = NULL;
> }
> + qemu_mutex_unlock(&qemu_logfile_mutex);
> }
>
> const QEMULogItem qemu_log_items[] = {
--
Alex Bennée
- [PATCH v2 0/6] Make the qemu_logfile handle thread safe., Robert Foley, 2019/11/15
- [PATCH v2 1/6] Fix double free issue in qemu_set_log_filename()., Robert Foley, 2019/11/15
- [PATCH v2 3/6] Add a mutex to guarantee single writer to qemu_logfile handle., Robert Foley, 2019/11/15
- Re: [PATCH v2 3/6] Add a mutex to guarantee single writer to qemu_logfile handle.,
Alex Bennée <=
- [PATCH v2 2/6] Cleaned up flow of code in qemu_set_log(), to simplify and clarify., Robert Foley, 2019/11/15
- [PATCH v2 4/6] qemu_log_lock/unlock now preserves the qemu_logfile handle., Robert Foley, 2019/11/15
- [PATCH v2 5/6] Add use of RCU for qemu_logfile., Robert Foley, 2019/11/15