[PATCH 18/21] log: enable directing log messages to data recorder

["Daniel P. Berrangé" <berrange@redhat.com>]

Currently the log APIs can output messages to stderr, a named
loge file, or discarded to /dev/null.  Introduce a "tldr" log
mask category which causes log messages to be directed to the
data recorder.

This this output is mutually exclusive with file based logging
and only captures single line logs emitted with qemu_log() or
qemu_log_mask(). Log callers using direct FILE* access will be
discarded. This is sufficient for the primary intended use case
which is to collect output from the 'log' trace backend.

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
---
 include/qemu/log.h |  1 +
 util/log.c         | 42 +++++++++++++++++++++++++++++++++---------
 2 files changed, 34 insertions(+), 9 deletions(-)

diff --git a/include/qemu/log.h b/include/qemu/log.h
index 92956e5d0f5..47d89681d8e 100644
--- a/include/qemu/log.h
+++ b/include/qemu/log.h
@@ -38,6 +38,7 @@ bool qemu_log_separate(void);
 #define CPU_LOG_TB_VPU     (1u << 21)
 #define LOG_TB_OP_PLUGIN   (1u << 22)
 #define LOG_INVALID_MEM    (1u << 23)
+#define LOG_TLDR           (1u << 24)
 
 /* Lock/unlock output. */
 
diff --git a/util/log.c b/util/log.c
index 7cffbc1bf89..df7499012f6 100644
--- a/util/log.c
+++ b/util/log.c
@@ -27,6 +27,7 @@
 #include "qemu/thread.h"
 #include "qemu/lockable.h"
 #include "qemu/rcu.h"
+#include "qemu/tldr.h"
 #ifdef CONFIG_LINUX
 #include <sys/syscall.h>
 #endif
@@ -172,12 +173,20 @@ void qemu_log_unlock(FILE *logfile)
 
 void qemu_log(const char *fmt, ...)
 {
-    FILE *f = qemu_log_trylock_with_context();
-    if (f) {
-        va_list ap;
-        va_start(ap, fmt);
-        vfprintf(f, fmt, ap);
-        va_end(ap);
+    va_list ap;
+    if (qemu_loglevel & LOG_TLDR) {
+        if (qtldr_msg_enabled(QTLDR_MSG_BUCKET_TYPE_LOG)) {
+            va_start(ap, fmt);
+            qtldr_msg_record_vprintf(QTLDR_MSG_BUCKET_TYPE_LOG, fmt, ap);
+            va_end(ap);
+        }
+    } else {
+        FILE *f = qemu_log_trylock_with_context();
+        if (f) {
+            va_start(ap, fmt);
+            vfprintf(f, fmt, ap);
+            va_end(ap);
+        }
         qemu_log_unlock(f);
     }
 }
@@ -236,6 +245,7 @@ static bool qemu_set_log_internal(const char *filename, bool changed_name,
     bool need_to_open_file;
     bool daemonized;
     bool per_thread;
+    bool tldr;
     FILE *logfile;
 
     QEMU_LOCK_GUARD(&global_mutex);
@@ -251,8 +261,20 @@ static bool qemu_set_log_internal(const char *filename, bool changed_name,
     }
 
     per_thread = log_flags & LOG_PER_THREAD;
+    tldr = log_flags & LOG_TLDR;
 
-    if (changed_name) {
+    if (tldr) {
+        if (filename) {
+            error_setg(errp, "Cannot enable TLDR with a log file");
+            return false;
+        }
+        if (per_thread) {
+            error_setg(errp, "Cannot enable TLDR with per-thread log files");
+            return false;
+        }
+    }
+
+    if (changed_name && !tldr) {
         char *newname = NULL;
 
         /*
@@ -282,7 +304,7 @@ static bool qemu_set_log_internal(const char *filename, bool changed_name,
         g_free(global_filename);
         global_filename = newname;
         filename = newname;
-    } else {
+    } else if (!tldr) {
         filename = global_filename;
         if (per_thread &&
             valid_filename_template(filename, true, errp) == vft_error) {
@@ -309,7 +331,7 @@ static bool qemu_set_log_internal(const char *filename, bool changed_name,
          * stderr or to a file (if there is a filename).
          * If per-thread, open the file for each thread in qemu_log_trylock().
          */
-        need_to_open_file = qemu_loglevel && !log_per_thread;
+        need_to_open_file = qemu_loglevel && !log_per_thread && !tldr;
     } else {
         /*
          * If we are daemonized, we will only log if there is a filename.
@@ -531,6 +553,8 @@ const QEMULogItem qemu_log_items[] = {
       "include VPU registers in the 'cpu' logging" },
     { LOG_INVALID_MEM, "invalid_mem",
       "log invalid memory accesses" },
+    { LOG_TLDR, "tldr",
+      "log to QEMU data recorder instead ofa file" },
     { 0, NULL, NULL },
 };
 
-- 
2.56.0