rust/qemu-api: log: implement io::Write

This makes it possible to lock the log file; it also makes log_mask_ln!
not allocate memory when logging a constant string.

Reviewed-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Manos Pitsidianakis <manos.pitsidianakis@linaro.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/util/log.c b/util/log.c
index b87d399e4c..58d24de48a 100644
--- a/util/log.c
+++ b/util/log.c
@@ -558,3 +558,15 @@ void qemu_print_log_usage(FILE *f)
     fprintf(f, "\nUse \"-d trace:help\" to get a list of trace events.\n\n");
 #endif
 }
+
+#ifdef CONFIG_HAVE_RUST
+ssize_t rust_fwrite(const void *ptr, size_t size, size_t nmemb, FILE *stream)
+{
+    /*
+     * Same as fwrite, but return -errno because Rust libc does not provide
+     * portable access to errno. :(
+     */
+    int ret = fwrite(ptr, size, nmemb, stream);
+    return ret < 0 ? -errno : 0;
+}
+#endif