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util/log: Support per-thread log files

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Add a new log flag, tid, to turn this feature on.
Require the log filename to be set, and to contain %d.

Do not allow tid to be turned off once it is on, nor let
the filename be change thereafter.  This avoids the need
for signalling each thread to re-open on a name change.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220417183019.755276-40-richard.henderson@linaro.org>
This commit is contained in:
Richard Henderson 2022-04-17 11:30:19 -07:00
parent 30f5a73ac3
commit 4e51069d67
2 changed files with 128 additions and 36 deletions
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1
include/qemu/log.h
View File

@ -34,6 +34,7 @@ bool qemu_log_separate(void);
#define CPU_LOG_PLUGIN (1 << 18)
/* LOG_STRACE is used for user-mode strace logging. */
#define LOG_STRACE (1 << 19)
#define LOG_PER_THREAD (1 << 20)
/* Lock/unlock output. */

149
util/log.c
View File

@ -27,6 +27,9 @@
#include "qemu/thread.h"
#include "qemu/lockable.h"
#include "qemu/rcu.h"
#ifdef CONFIG_LINUX
#include <sys/syscall.h>
#endif
typedef struct RCUCloseFILE {
@ -38,22 +41,40 @@ typedef struct RCUCloseFILE {
static QemuMutex global_mutex;
static char *global_filename;
static FILE *global_file;
static __thread FILE *thread_file;
int qemu_loglevel;
static int log_append = 0;
static bool log_append;
static bool log_per_thread;
static GArray *debug_regions;
/* Returns true if qemu_log() will really write somewhere. */
bool qemu_log_enabled(void)
{
return qatomic_read(&global_file) != NULL;
return log_per_thread || qatomic_read(&global_file) != NULL;
}
/* Returns true if qemu_log() will write somewhere other than stderr. */
bool qemu_log_separate(void)
{
if (log_per_thread) {
return true;
} else {
FILE *logfile = qatomic_read(&global_file);
return logfile && logfile != stderr;
}
}
static int log_thread_id(void)
{
#ifdef CONFIG_GETTID
return gettid();
#elif defined(SYS_gettid)
return syscall(SYS_gettid);
#else
static int counter;
return qatomic_fetch_inc(&counter);
#endif
}
/* Lock/unlock output. */
@ -62,6 +83,17 @@ FILE *qemu_log_trylock(void)
{
FILE *logfile;
logfile = thread_file;
if (!logfile) {
if (log_per_thread) {
g_autofree char *filename
= g_strdup_printf(global_filename, log_thread_id());
logfile = fopen(filename, "w");
if (!logfile) {
return NULL;
}
thread_file = logfile;
} else {
rcu_read_lock();
/*
* FIXME: typeof_strip_qual, as used by qatomic_rcu_read,
@ -71,11 +103,14 @@ FILE *qemu_log_trylock(void)
* which does work with typeof_strip_qual.
*/
logfile = qatomic_rcu_read((void **)&global_file);
if (logfile) {
qemu_flockfile(logfile);
} else {
if (!logfile) {
rcu_read_unlock();
return NULL;
}
}
}
qemu_flockfile(logfile);
return logfile;
}
@ -84,8 +119,10 @@ void qemu_log_unlock(FILE *logfile)
if (logfile) {
fflush(logfile);
qemu_funlockfile(logfile);
if (!log_per_thread) {
rcu_read_unlock();
}
}
}
void qemu_log(const char *fmt, ...)
@ -112,40 +149,81 @@ static void rcu_close_file(RCUCloseFILE *r)
g_free(r);
}
/* enable or disable low levels log */
static bool qemu_set_log_internal(const char *filename, bool changed_name,
int log_flags, Error **errp)
{
bool need_to_open_file;
bool daemonized;
FILE *logfile;
QEMU_LOCK_GUARD(&global_mutex);
logfile = global_file;
if (changed_name) {
char *newname = NULL;
/*
* Allow the user to include %d in their logfile which will be
* substituted with the current PID. This is useful for debugging many
* nested linux-user tasks but will result in lots of logs.
/**
* valid_filename_template:
*
* filename may be NULL. In that case, log output is sent to stderr
* Validate the filename template. Require %d if per_thread, allow it
* otherwise; require no other % within the template.
*/
typedef enum {
vft_error,
vft_stderr,
vft_strdup,
vft_pid_printf,
} ValidFilenameTemplateResult;
static ValidFilenameTemplateResult
valid_filename_template(const char *filename, bool per_thread, Error **errp)
{
if (filename) {
char *pidstr = strstr(filename, "%");
if (pidstr) {
/* We only accept one %d, no other format strings */
if (pidstr[1] != 'd' || strchr(pidstr + 2, '%')) {
error_setg(errp, "Bad logfile format: %s", filename);
error_setg(errp, "Bad logfile template: %s", filename);
return 0;
}
return per_thread ? vft_strdup : vft_pid_printf;
}
}
if (per_thread) {
error_setg(errp, "Filename template with '%%d' required for 'tid'");
return vft_error;
}
return filename ? vft_strdup : vft_stderr;
}
/* enable or disable low levels log */
static bool qemu_set_log_internal(const char *filename, bool changed_name,
int log_flags, Error **errp)
{
bool need_to_open_file;
bool daemonized;
bool per_thread;
FILE *logfile;
QEMU_LOCK_GUARD(&global_mutex);
logfile = global_file;
per_thread = log_flags & LOG_PER_THREAD;
if (changed_name) {
char *newname = NULL;
/*
* Once threads start opening their own log files, we have no
* easy mechanism to tell them all to close and re-open.
* There seems little cause to do so either -- this option
* will most often be used at user-only startup.
*/
if (log_per_thread) {
error_setg(errp, "Cannot change log filename after setting 'tid'");
return false;
}
newname = g_strdup_printf(filename, getpid());
} else {
switch (valid_filename_template(filename, per_thread, errp)) {
case vft_error:
return false;
case vft_stderr:
break;
case vft_strdup:
newname = g_strdup(filename);
}
break;
case vft_pid_printf:
newname = g_strdup_printf(filename, getpid());
break;
}
g_free(global_filename);
@ -153,8 +231,18 @@ static bool qemu_set_log_internal(const char *filename, bool changed_name,
filename = newname;
} else {
filename = global_filename;
if (per_thread &&
valid_filename_template(filename, true, errp) == vft_error) {
return false;
}
}
/* Once the per-thread flag is set, it cannot be unset. */
if (per_thread) {
log_per_thread = true;
}
/* The flag itself is not relevant for need_to_open_file. */
log_flags &= ~LOG_PER_THREAD;
#ifdef CONFIG_TRACE_LOG
log_flags |= LOG_TRACE;
#endif
@ -163,12 +251,13 @@ static bool qemu_set_log_internal(const char *filename, bool changed_name,
/*
* In all cases we only log if qemu_loglevel is set.
* Also:
* If per-thread, open the file for each thread in qemu_log_lock.
* If not daemonized we will always log either to stderr
* or to a file (if there is a filename).
* If we are daemonized, we will only log if there is a filename.
*/
daemonized = is_daemonized();
need_to_open_file = log_flags && (!daemonized || filename);
need_to_open_file = log_flags && !per_thread && (!daemonized || filename);
if (logfile && (!need_to_open_file || changed_name)) {
qatomic_rcu_set(&global_file, NULL);
@ -354,6 +443,8 @@ const QEMULogItem qemu_log_items[] = {
#endif
{ LOG_STRACE, "strace",
"log every user-mode syscall, its input, and its result" },
{ LOG_PER_THREAD, "tid",
"open a separate log file per thread; filename must contain '%d'" },
{ 0, NULL, NULL },
};