util/log: Rename qemu_log_lock to qemu_log_trylock

This function can fail, which makes it more like ftrylockfile
or pthread_mutex_trylock than flockfile or pthread_mutex_lock,
so rename it.

To closer match the other trylock functions, release rcu_read_lock
along the failure path, so that qemu_log_unlock need not be called
on failure.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20220417183019.755276-8-richard.henderson@linaro.org>

accel/tcg/cpu-exec.c

@@ -214,7 +214,7 @@ static inline void log_cpu_exec(target_ulong pc, CPUState *cpu,
 
 #if defined(DEBUG_DISAS)
         if (qemu_loglevel_mask(CPU_LOG_TB_CPU)) {
-            FILE *logfile = qemu_log_lock();
+            FILE *logfile = qemu_log_trylock();
             int flags = 0;
 
             if (qemu_loglevel_mask(CPU_LOG_TB_FPU)) {

accel/tcg/translate-all.c

@@ -1527,7 +1527,7 @@ TranslationBlock *tb_gen_code(CPUState *cpu,
 #ifdef DEBUG_DISAS
     if (qemu_loglevel_mask(CPU_LOG_TB_OUT_ASM) &&
         qemu_log_in_addr_range(tb->pc)) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         int code_size, data_size;
         const tcg_target_ulong *rx_data_gen_ptr;
         size_t chunk_start;

accel/tcg/translator.c

@@ -139,7 +139,7 @@ void translator_loop(const TranslatorOps *ops, DisasContextBase *db,
 #ifdef DEBUG_DISAS
     if (qemu_loglevel_mask(CPU_LOG_TB_IN_ASM)
         && qemu_log_in_addr_range(db->pc_first)) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         qemu_log("----------------\n");
         ops->disas_log(db, cpu);
         qemu_log("\n");

cpu.c

@@ -399,7 +399,7 @@ void cpu_abort(CPUState *cpu, const char *fmt, ...)
     fprintf(stderr, "\n");
     cpu_dump_state(cpu, stderr, CPU_DUMP_FPU | CPU_DUMP_CCOP);
     if (qemu_log_separate()) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         qemu_log("qemu: fatal: ");
         qemu_log_vprintf(fmt, ap2);
         qemu_log("\n");

hw/net/can/can_sja1000.c

@@ -247,7 +247,7 @@ int can_sja_accept_filter(CanSJA1000State *s,
 static void can_display_msg(const char *prefix, const qemu_can_frame *msg)
 {
     int i;
-    FILE *logfile = qemu_log_lock();
+    FILE *logfile = qemu_log_trylock();
 
     qemu_log("%s%03X [%01d] %s %s",
              prefix,

include/exec/log.h

@@ -71,7 +71,7 @@ static inline void log_disas(const void *code, unsigned long size)
 /* page_dump() output to the log file: */
 static inline void log_page_dump(const char *operation)
 {
-    FILE *logfile = qemu_log_lock();
+    FILE *logfile = qemu_log_trylock();
     if (logfile) {
         qemu_log("page layout changed following %s\n", operation);
         page_dump(logfile);

include/qemu/log.h

@@ -67,7 +67,7 @@ static inline bool qemu_log_separate(void)
 
 /* Lock/unlock output. */
 
-FILE *qemu_log_lock(void);
+FILE *qemu_log_trylock(void);
 void qemu_log_unlock(FILE *fd);
 
 /* Logging functions: */

net/can/can_socketcan.c

@@ -76,7 +76,7 @@ QEMU_BUILD_BUG_ON(offsetof(qemu_can_frame, data)
 static void can_host_socketcan_display_msg(struct qemu_can_frame *msg)
 {
     int i;
-    FILE *logfile = qemu_log_lock();
+    FILE *logfile = qemu_log_trylock();
     qemu_log("[cansocketcan]: %03X [%01d] %s %s",
              msg->can_id & QEMU_CAN_EFF_MASK,
              msg->can_dlc,

target/i386/tcg/translate.c

@@ -2580,7 +2580,7 @@ static void gen_unknown_opcode(CPUX86State *env, DisasContext *s)
     gen_illegal_opcode(s);
 
     if (qemu_loglevel_mask(LOG_UNIMP)) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         target_ulong pc = s->pc_start, end = s->pc;
 
         qemu_log("ILLOPC: " TARGET_FMT_lx ":", pc);

tcg/tcg.c

@@ -756,7 +756,7 @@ void tcg_prologue_init(TCGContext *s)
 
 #ifdef DEBUG_DISAS
     if (qemu_loglevel_mask(CPU_LOG_TB_OUT_ASM)) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         qemu_log("PROLOGUE: [size=%zu]\n", prologue_size);
         if (s->data_gen_ptr) {
             size_t code_size = s->data_gen_ptr - s->code_gen_ptr;
@@ -4200,7 +4200,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
 #ifdef DEBUG_DISAS
     if (unlikely(qemu_loglevel_mask(CPU_LOG_TB_OP)
                  && qemu_log_in_addr_range(tb->pc))) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         qemu_log("OP:\n");
         tcg_dump_ops(s, false);
         qemu_log("\n");
@@ -4245,7 +4245,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
 #ifdef DEBUG_DISAS
         if (unlikely(qemu_loglevel_mask(CPU_LOG_TB_OP_IND)
                      && qemu_log_in_addr_range(tb->pc))) {
-            FILE *logfile = qemu_log_lock();
+            FILE *logfile = qemu_log_trylock();
             qemu_log("OP before indirect lowering:\n");
             tcg_dump_ops(s, false);
             qemu_log("\n");
@@ -4266,7 +4266,7 @@ int tcg_gen_code(TCGContext *s, TranslationBlock *tb)
 #ifdef DEBUG_DISAS
     if (unlikely(qemu_loglevel_mask(CPU_LOG_TB_OP_OPT)
                  && qemu_log_in_addr_range(tb->pc))) {
-        FILE *logfile = qemu_log_lock();
+        FILE *logfile = qemu_log_trylock();
         qemu_log("OP after optimization and liveness analysis:\n");
         tcg_dump_ops(s, true);
         qemu_log("\n");

tests/unit/test-logging.c

@@ -162,7 +162,7 @@ static void test_logfile_lock(gconstpointer data)
      * our handle remains valid for use due to RCU.
      */
     qemu_set_log_filename(file_path, &error_abort);
-    logfile = qemu_log_lock();
+    logfile = qemu_log_trylock();
     g_assert(logfile);
     fprintf(logfile, "%s 1st write to file\n", __func__);
     fflush(logfile);

util/log.c

@@ -36,15 +36,17 @@ static GArray *debug_regions;
 
 /* Lock/unlock output. */
 
-FILE *qemu_log_lock(void)
+FILE *qemu_log_trylock(void)
 {
     QemuLogFile *logfile;
+
     rcu_read_lock();
     logfile = qatomic_rcu_read(&qemu_logfile);
     if (logfile) {
         qemu_flockfile(logfile->fd);
         return logfile->fd;
     } else {
+        rcu_read_unlock();
         return NULL;
     }
 }
@@ -53,8 +55,8 @@ void qemu_log_unlock(FILE *fd)
 {
     if (fd) {
         qemu_funlockfile(fd);
+        rcu_read_unlock();
     }
-    rcu_read_unlock();
 }
 
 /* Return the number of characters emitted.  */