fsmonitor: enhance existing comments, clarify trivial response handling

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

diff --git a/fsmonitor.c b/fsmonitor.c
index ab9bfc60b34e3146f73194d01cf8963a90f1d768..448d0ee33f5a79eef0addb102f4871c0ea841eaa 100644 (file)
--- a/fsmonitor.c
+++ b/fsmonitor.c
@@ -168,29 +168,15 @@ static int query_fsmonitor(int version, const char *last_update, struct strbuf *
 
        if (result)
                trace2_data_intmax("fsm_hook", NULL, "query/failed", result);
-       else {
+       else
                trace2_data_intmax("fsm_hook", NULL, "query/response-length",
                                   query_result->len);
 
-               if (fsmonitor_is_trivial_response(query_result))
-                       trace2_data_intmax("fsm_hook", NULL,
-                                          "query/trivial-response", 1);
-       }
-
        trace2_region_leave("fsm_hook", "query", NULL);
 
        return result;
 }
 
-int fsmonitor_is_trivial_response(const struct strbuf *query_result)
-{
-       static char trivial_response[3] = { '\0', '/', '\0' };
-
-       return query_result->len >= 3 &&
-               !memcmp(trivial_response,
-                       &query_result->buf[query_result->len - 3], 3);
-}
-
 static void fsmonitor_refresh_callback(struct index_state *istate, char *name)
 {
        int i, len = strlen(name);
@@ -238,6 +224,7 @@ void refresh_fsmonitor(struct index_state *istate)
        struct strbuf last_update_token = STRBUF_INIT;
        char *buf;
        unsigned int i;
+       int is_trivial = 0;
 
        if (!core_fsmonitor || istate->fsmonitor_has_run_once)
                return;
@@ -283,6 +270,7 @@ void refresh_fsmonitor(struct index_state *istate)
                                        query_success = 0;
                                } else {
                                        bol = last_update_token.len + 1;
+                                       is_trivial = query_result.buf[bol] == '/';
                                }
                        } else if (hook_version < 0) {
                                hook_version = HOOK_INTERFACE_VERSION1;
@@ -294,16 +282,38 @@ void refresh_fsmonitor(struct index_state *istate)
                if (hook_version == HOOK_INTERFACE_VERSION1) {
                        query_success = !query_fsmonitor(HOOK_INTERFACE_VERSION1,
                                istate->fsmonitor_last_update, &query_result);
+                       if (query_success)
+                               is_trivial = query_result.buf[0] == '/';
                }
 
+               if (is_trivial)
+                       trace2_data_intmax("fsm_hook", NULL,
+                                          "query/trivial-response", 1);
+
                trace_performance_since(last_update, "fsmonitor process '%s'", core_fsmonitor);
                trace_printf_key(&trace_fsmonitor, "fsmonitor process '%s' returned %s",
                        core_fsmonitor, query_success ? "success" : "failure");
        }
 
-       /* a fsmonitor process can return '/' to indicate all entries are invalid */
-       if (query_success && query_result.buf[bol] != '/') {
-               /* Mark all entries returned by the monitor as dirty */
+       /*
+        * The response from FSMonitor (excluding the header token) is
+        * either:
+        *
+        * [a] a (possibly empty) list of NUL delimited relative
+        *     pathnames of changed paths.  This list can contain
+        *     files and directories.  Directories have a trailing
+        *     slash.
+        *
+        * [b] a single '/' to indicate the provider had no
+        *     information and that we should consider everything
+        *     invalid.  We call this a trivial response.
+        */
+       if (query_success && !is_trivial) {
+               /*
+                * Mark all pathnames returned by the monitor as dirty.
+                *
+                * This updates both the cache-entries and the untracked-cache.
+                */
                buf = query_result.buf;
                for (i = bol; i < query_result.len; i++) {
                        if (buf[i] != '\0')
@@ -318,11 +328,16 @@ void refresh_fsmonitor(struct index_state *istate)
                if (istate->untracked)
                        istate->untracked->use_fsmonitor = 1;
        } else {
-
-               /* We only want to run the post index changed hook if we've actually changed entries, so keep track
-                * if we actually changed entries or not */
+               /*
+                * We failed to get a response or received a trivial response,
+                * so invalidate everything.
+                *
+                * We only want to run the post index changed hook if
+                * we've actually changed entries, so keep track if we
+                * actually changed entries or not.
+                */
                int is_cache_changed = 0;
-               /* Mark all entries invalid */
+
                for (i = 0; i < istate->cache_nr; i++) {
                        if (istate->cache[i]->ce_flags & CE_FSMONITOR_VALID) {
                                is_cache_changed = 1;
@@ -330,7 +345,10 @@ void refresh_fsmonitor(struct index_state *istate)
                        }
                }
 
-               /* If we're going to check every file, ensure we save the results */
+               /*
+                * If we're going to check every file, ensure we save
+                * the results.
+                */
                if (is_cache_changed)
                        istate->cache_changed |= FSMONITOR_CHANGED;