4 files changed, 63 insertions, 10 deletions

diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
index 7d96f33420..5dda0ca1cd 100644
--- a/trace2/tr2_dst.c
+++ b/trace2/tr2_dst.c
@@ -1,14 +1,13 @@
 #include "cache.h"
 #include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
 #include "trace2/tr2_sysenv.h"
 
 /*
- * If a Trace2 target cannot be opened for writing, we should issue a
- * warning to stderr, but this is very annoying if the target is a pipe
- * or socket and beyond the user's control -- especially since every
- * git command (and sub-command) will print the message.  So we silently
- * eat these warnings and just discard the trace data.
+ * How many attempts we will make at creating an automatically-named trace file.
  */
+#define MAX_AUTO_ATTEMPTS 10
+
 static int tr2_dst_want_warning(void)
 {
 	static int tr2env_dst_debug = -1;
@@ -33,6 +32,56 @@ void tr2_dst_trace_disable(struct tr2_dst *dst)
 	dst->need_close = 0;
 }
 
+static int tr2_dst_try_auto_path(struct tr2_dst *dst, const char *tgt_prefix)
+{
+	int fd;
+	const char *last_slash, *sid = tr2_sid_get();
+	struct strbuf path = STRBUF_INIT;
+	size_t base_path_len;
+	unsigned attempt_count;
+
+	last_slash = strrchr(sid, '/');
+	if (last_slash)
+		sid = last_slash + 1;
+
+	strbuf_addstr(&path, tgt_prefix);
+	if (!is_dir_sep(path.buf[path.len - 1]))
+		strbuf_addch(&path, '/');
+	strbuf_addstr(&path, sid);
+	base_path_len = path.len;
+
+	for (attempt_count = 0; attempt_count < MAX_AUTO_ATTEMPTS; attempt_count++) {
+		if (attempt_count > 0) {
+			strbuf_setlen(&path, base_path_len);
+			strbuf_addf(&path, ".%d", attempt_count);
+		}
+
+		fd = open(path.buf, O_WRONLY | O_CREAT | O_EXCL, 0666);
+		if (fd != -1)
+			break;
+	}
+
+	if (fd == -1) {
+		if (tr2_dst_want_warning())
+			warning("trace2: could not open '%.*s' for '%s' tracing: %s",
+				(int) base_path_len, path.buf,
+				tr2_sysenv_display_name(dst->sysenv_var),
+				strerror(errno));
+
+		tr2_dst_trace_disable(dst);
+		strbuf_release(&path);
+		return 0;
+	}
+
+	strbuf_release(&path);
+
+	dst->fd = fd;
+	dst->need_close = 1;
+	dst->initialized = 1;
+
+	return dst->fd;
+}
+
 static int tr2_dst_try_path(struct tr2_dst *dst, const char *tgt_value)
 {
 	int fd = open(tgt_value, O_WRONLY | O_APPEND | O_CREAT, 0666);
@@ -203,8 +252,12 @@ int tr2_dst_get_trace_fd(struct tr2_dst *dst)
 		return dst->fd;
 	}
 
-	if (is_absolute_path(tgt_value))
-		return tr2_dst_try_path(dst, tgt_value);
+	if (is_absolute_path(tgt_value)) {
+		if (is_directory(tgt_value))
+			return tr2_dst_try_auto_path(dst, tgt_value);
+		else
+			return tr2_dst_try_path(dst, tgt_value);
+	}
 
 #ifndef NO_UNIX_SOCKETS
 	if (starts_with(tgt_value, PREFIX_AF_UNIX))
diff --git a/trace2/tr2_tgt_event.c b/trace2/tr2_tgt_event.c
index 2c97cf54be..c2852d1bd2 100644
--- a/trace2/tr2_tgt_event.c
+++ b/trace2/tr2_tgt_event.c
@@ -193,7 +193,7 @@ static void fn_atexit(uint64_t us_elapsed_absolute, int code)
 static void maybe_add_string_va(struct json_writer *jw, const char *field_name,
 				const char *fmt, va_list ap)
 {
-	if (fmt && *fmt && ap) {
+	if (fmt && *fmt) {
 		va_list copy_ap;
 		struct strbuf buf = STRBUF_INIT;
 
diff --git a/trace2/tr2_tgt_normal.c b/trace2/tr2_tgt_normal.c
index 1ce6f97863..00b116d797 100644
--- a/trace2/tr2_tgt_normal.c
+++ b/trace2/tr2_tgt_normal.c
@@ -127,7 +127,7 @@ static void fn_atexit(uint64_t us_elapsed_absolute, int code)
 static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
 				   va_list ap)
 {
-	if (fmt && *fmt && ap) {
+	if (fmt && *fmt) {
 		va_list copy_ap;
 
 		va_copy(copy_ap, ap);
diff --git a/trace2/tr2_tgt_perf.c b/trace2/tr2_tgt_perf.c
index 328d2234bd..ea0cbbe13e 100644
--- a/trace2/tr2_tgt_perf.c
+++ b/trace2/tr2_tgt_perf.c
@@ -212,7 +212,7 @@ static void fn_atexit(uint64_t us_elapsed_absolute, int code)
 static void maybe_append_string_va(struct strbuf *buf, const char *fmt,
 				   va_list ap)
 {
-	if (fmt && *fmt && ap) {
+	if (fmt && *fmt) {
 		va_list copy_ap;
 
 		va_copy(copy_ap, ap);