trace2: write to directory targets

When the value of a trace2 environment variable is an absolute path
referring to an existing directory, write output to files (one per
process) underneath the given directory. Files will be named according
to the final component of the trace2 SID, followed by a counter to avoid
potential collisions.

This makes it more convenient to collect traces for every git invocation
by unconditionally setting the relevant trace2 envvar to a constant
directory name.

Signed-off-by: Josh Steadmon <steadmon@google.com>
Reviewed-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 61 insertions, 2 deletions

diff --git a/trace2/tr2_dst.c b/trace2/tr2_dst.c
index fd490a4..c3d82ca 100644
--- a/trace2/tr2_dst.c
+++ b/trace2/tr2_dst.c
@@ -1,5 +1,6 @@
 #include "cache.h"
 #include "trace2/tr2_dst.h"
+#include "trace2/tr2_sid.h"
 
 /*
  * If a Trace2 target cannot be opened for writing, we should issue a
@@ -12,6 +13,11 @@
  */
 #define TR2_ENVVAR_DST_DEBUG "GIT_TR2_DST_DEBUG"
 
+/*
+ * 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;
@@ -36,6 +42,55 @@ 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,
+				dst->env_var_name, 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);
@@ -202,8 +257,12 @@ 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))