[PATCH v2 1/2] util/log: Derive thread id from getpid() on hosts w/o gettid() syscall

[Greg Kurz <groug@kaod.org>]

A subsequent patch needs to be able to differentiate the main QEMU
thread from other threads. An obvious way to do so is to compare
log_thread_id() and getpid(), based on the fact that they are equal
for the main thread on systems that have the gettid() syscall (e.g.
linux).

Adapt the fallback code for systems without gettid() to provide the
same assumption.

Suggested-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
---
 util/log.c | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/util/log.c b/util/log.c
index d6eb0378c3a3..e1c2535cfcd2 100644
--- a/util/log.c
+++ b/util/log.c
@@ -72,8 +72,13 @@ static int log_thread_id(void)
 #elif defined(SYS_gettid)
     return syscall(SYS_gettid);
 #else
+    static __thread int my_id = -1;
     static int counter;
-    return qatomic_fetch_inc(&counter);
+
+    if (my_id == -1) {
+        my_id = getpid() + qatomic_fetch_inc(&counter);
+    }
+    return my_id;
 #endif
 }
 
-- 
2.37.3