linux-user: Use `qemu_log' for strace

This change switches linux-user strace logging to use the newer `qemu_log`
logging subsystem rather than the older `gemu_log` (notice the "g")
logger. `qemu_log` has several advantages, namely that it allows logging
to a file, and provides a more unified interface for configuration
of logging (via the QEMU_LOG environment variable or options).

This change introduces a new log mask: `LOG_STRACE` which is used for
logging of user-mode strace messages.

Reviewed-by: Laurent Vivier <laurent@vivier.eu>
Signed-off-by: Josh Kunz <jkz@google.com>
Message-Id: <20200204025416.111409-3-jkz@google.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>

1 files changed, 23 insertions, 7 deletions

diff --git a/linux-user/main.c b/linux-user/main.c
index fba833a..8f1d07c 100644
--- a/linux-user/main.c
+++ b/linux-user/main.c
@@ -61,6 +61,19 @@ unsigned long guest_base;
 int have_guest_base;
 
 /*
+ * Used to implement backwards-compatibility for the `-strace`, and
+ * QEMU_STRACE options. Without this, the QEMU_LOG can be overwritten by
+ * -strace, or vice versa.
+ */
+static bool enable_strace;
+
+/*
+ * The last log mask given by the user in an environment variable or argument.
+ * Used to support command line arguments overriding environment variables.
+ */
+static int last_log_mask;
+
+/*
  * When running 32-on-64 we should make sure we can fit all of the possible
  * guest address space into a contiguous chunk of virtual host memory.
  *
@@ -223,15 +236,11 @@ static void handle_arg_help(const char *arg)
 
 static void handle_arg_log(const char *arg)
 {
-    int mask;
-
-    mask = qemu_str_to_log_mask(arg);
-    if (!mask) {
+    last_log_mask = qemu_str_to_log_mask(arg);
+    if (!last_log_mask) {
         qemu_print_log_usage(stdout);
         exit(EXIT_FAILURE);
     }
-    qemu_log_needs_buffers();
-    qemu_set_log(mask);
 }
 
 static void handle_arg_dfilter(const char *arg)
@@ -375,7 +384,7 @@ static void handle_arg_singlestep(const char *arg)
 
 static void handle_arg_strace(const char *arg)
 {
-    do_strace = 1;
+    enable_strace = true;
 }
 
 static void handle_arg_version(const char *arg)
@@ -629,6 +638,7 @@ int main(int argc, char **argv, char **envp)
     int i;
     int ret;
     int execfd;
+    int log_mask;
     unsigned long max_reserved_va;
 
     error_init(argv[0]);
@@ -661,6 +671,12 @@ int main(int argc, char **argv, char **envp)
 
     optind = parse_args(argc, argv);
 
+    log_mask = last_log_mask | (enable_strace ? LOG_STRACE : 0);
+    if (log_mask) {
+        qemu_log_needs_buffers();
+        qemu_set_log(log_mask);
+    }
+
     if (!trace_init_backends()) {
         exit(1);
     }