util/log: Support per-thread log files
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>
diff --git a/util/log.c b/util/log.c
index df07107..d6eb037 100644
--- a/util/log.c
+++ b/util/log.c
@@ -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 @@
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)
{
- FILE *logfile = qatomic_read(&global_file);
- return logfile && logfile != stderr;
+ 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. */
@@ -62,20 +83,34 @@
{
FILE *logfile;
- rcu_read_lock();
- /*
- * FIXME: typeof_strip_qual, as used by qatomic_rcu_read,
- * does not work with pointers to undefined structures,
- * such as we have with struct _IO_FILE and musl libc.
- * Since all we want is a read of a pointer, cast to void**,
- * which does work with typeof_strip_qual.
- */
- logfile = qatomic_rcu_read((void **)&global_file);
- if (logfile) {
- qemu_flockfile(logfile);
- } else {
- rcu_read_unlock();
+ 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,
+ * does not work with pointers to undefined structures,
+ * such as we have with struct _IO_FILE and musl libc.
+ * Since all we want is a read of a pointer, cast to void**,
+ * which does work with typeof_strip_qual.
+ */
+ logfile = qatomic_rcu_read((void **)&global_file);
+ if (!logfile) {
+ rcu_read_unlock();
+ return NULL;
+ }
+ }
}
+
+ qemu_flockfile(logfile);
return logfile;
}
@@ -84,7 +119,9 @@
if (logfile) {
fflush(logfile);
qemu_funlockfile(logfile);
- rcu_read_unlock();
+ if (!log_per_thread) {
+ rcu_read_unlock();
+ }
}
}
@@ -112,40 +149,81 @@
g_free(r);
}
+/**
+ * valid_filename_template:
+ *
+ * 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 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;
/*
- * 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.
- *
- * filename may be NULL. In that case, log output is sent to stderr
+ * 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 (filename) {
- char *pidstr = strstr(filename, "%");
+ if (log_per_thread) {
+ error_setg(errp, "Cannot change log filename after setting 'tid'");
+ return false;
+ }
- 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);
- return false;
- }
- newname = g_strdup_printf(filename, getpid());
- } else {
- newname = g_strdup(filename);
- }
+ 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 @@
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 @@
/*
* 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 @@
#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 },
};
