log_ref_setup(): improve robustness against races

diff --git a/trace.c b/trace.c
index 4aeea60973100bfed212842cb46a5a81154b7781..7508aea028bb642140cabcd02c37cdaf3a21234c 100644 (file)
--- a/trace.c
+++ b/trace.c
@@ -25,15 +25,25 @@
 #include "cache.h"
 #include "quote.h"
 
+/*
+ * "Normalize" a key argument by converting NULL to our trace_default,
+ * and otherwise passing through the value. All caller-facing functions
+ * should normalize their inputs in this way, though most get it
+ * for free by calling get_trace_fd() (directly or indirectly).
+ */
+static void normalize_trace_key(struct trace_key **key)
+{
+       static struct trace_key trace_default = { "GIT_TRACE" };
+       if (!*key)
+               *key = &trace_default;
+}
+
 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
 {
-       static struct trace_key trace_default = { "GIT_TRACE" };
        const char *trace;
 
-       /* use default "GIT_TRACE" if NULL */
-       if (!key)
-               key = &trace_default;
+       normalize_trace_key(&key);
 
        /* don't open twice */
        if (key->initialized)
@@ -51,22 +61,19 @@ static int get_trace_fd(struct trace_key *key)
        else if (is_absolute_path(trace)) {
                int fd = open(trace, O_WRONLY | O_APPEND | O_CREAT, 0666);
                if (fd == -1) {
-                       fprintf(stderr,
-                               "Could not open '%s' for tracing: %s\n"
-                               "Defaulting to tracing on stderr...\n",
+                       warning("could not open '%s' for tracing: %s",
                                trace, strerror(errno));
-                       key->fd = STDERR_FILENO;
+                       trace_disable(key);
                } else {
                        key->fd = fd;
                        key->need_close = 1;
                }
        } else {
-               fprintf(stderr, "What does '%s' for %s mean?\n"
-                       "If you want to trace into a file, then please set "
-                       "%s to an absolute pathname (starting with /).\n"
-                       "Defaulting to tracing on stderr...\n",
-                       trace, key->key, key->key);
-               key->fd = STDERR_FILENO;
+               warning("unknown trace value for '%s': %s\n"
+                       "         If you want to trace into a file, then please set %s\n"
+                       "         to an absolute pathname (starting with /)",
+                       key->key, trace, key->key);
+               trace_disable(key);
        }
 
        key->initialized = 1;
@@ -75,6 +82,8 @@ static int get_trace_fd(struct trace_key *key)
 
 void trace_disable(struct trace_key *key)
 {
+       normalize_trace_key(&key);
+
        if (key->need_close)
                close(key->fd);
        key->fd = 0;
@@ -82,9 +91,6 @@ void trace_disable(struct trace_key *key)
        key->need_close = 0;
 }
 
-static const char err_msg[] = "Could not trace into fd given by "
-       "GIT_TRACE environment variable";
-
 static int prepare_trace_line(const char *file, int line,
                              struct trace_key *key, struct strbuf *buf)
 {
@@ -120,18 +126,27 @@ static int prepare_trace_line(const char *file, int line,
        return 1;
 }
 
+static void trace_write(struct trace_key *key, const void *buf, unsigned len)
+{
+       if (write_in_full(get_trace_fd(key), buf, len) < 0) {
+               normalize_trace_key(&key);
+               warning("unable to write trace for %s: %s",
+                       key->key, strerror(errno));
+               trace_disable(key);
+       }
+}
+
 void trace_verbatim(struct trace_key *key, const void *buf, unsigned len)
 {
        if (!trace_want(key))
                return;
-       write_or_whine_pipe(get_trace_fd(key), buf, len, err_msg);
+       trace_write(key, buf, len);
 }
 
 static void print_trace_line(struct trace_key *key, struct strbuf *buf)
 {
        strbuf_complete_line(buf);
-
-       write_or_whine_pipe(get_trace_fd(key), buf->buf, buf->len, err_msg);
+       trace_write(key, buf->buf, buf->len);
        strbuf_release(buf);
 }