log: Add locking to large logging blocks

Reuse the existing locking provided by stdio to keep in_asm, cpu,
op, op_opt, op_ind, and out_asm as contiguous blocks.

While it isn't possible to interleave e.g. in_asm or op_opt logs
because of the TB lock protecting all code generation, it is
possible to interleave cpu logs, or to interleave a cpu dump with
an out_asm dump.

For mingw32, we appear to have no viable solution for this.  The locking
functions are not properly exported from the system runtime library.

Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Richard Henderson <rth@twiddle.net>

include/qemu/log.h

@@ -51,6 +51,22 @@ static inline bool qemu_loglevel_mask(int mask)
     return (qemu_loglevel & mask) != 0;
 }
 
+/* Lock output for a series of related logs.  Since this is not needed
+ * for a single qemu_log / qemu_log_mask / qemu_log_mask_and_addr, we
+ * assume that qemu_loglevel_mask has already been tested, and that
+ * qemu_loglevel is never set when qemu_logfile is unset.
+ */
+
+static inline void qemu_log_lock(void)
+{
+    qemu_flockfile(qemu_logfile);
+}
+
+static inline void qemu_log_unlock(void)
+{
+    qemu_funlockfile(qemu_logfile);
+}
+
 /* Logging functions: */
 
 /* main logging function

include/sysemu/os-posix.h

@@ -87,4 +87,16 @@ void *qemu_alloc_stack(size_t *sz);
  */
 void qemu_free_stack(void *stack, size_t sz);
 
+/* POSIX and Mingw32 differ in the name of the stdio lock functions.  */
+
+static inline void qemu_flockfile(FILE *f)
+{
+    flockfile(f);
+}
+
+static inline void qemu_funlockfile(FILE *f)
+{
+    funlockfile(f);
+}
+
 #endif

include/sysemu/os-win32.h

@@ -103,6 +103,21 @@ static inline char *realpath(const char *path, char *resolved_path)
     return resolved_path;
 }
 
+/* ??? Mingw appears to export _lock_file and _unlock_file as the functions
+ * with which to lock a stdio handle.  But something is wrong in the markup,
+ * either in the header or the library, such that we get undefined references
+ * to "_imp___lock_file" etc when linking.  Since we seem to have no other
+ * alternative, and the usage within the logging functions isn't critical,
+ * ignore FILE locking.
+ */
+
+static inline void qemu_flockfile(FILE *f)
+{
+}
+
+static inline void qemu_funlockfile(FILE *f)
+{
+}
 
 /* We wrap all the sockets functions so that we can
  * set errno based on WSAGetLastError()