Re: [Census] So who uses git?

[Linus Torvalds <torvalds@osdl.org>]

On Tue, 31 Jan 2006, Linus Torvalds wrote:
> 
> We still have one unused bit in the cache-entry "ce_flags", so we wouldn't 
> even need to break any existing index files with it.

In case it wasn't clear, the _core_ of this optimization would be as 
simple as something like the appended.

The real meat is just making sure that CE_VALID gets set/cleared properly.

(That's also the most complex part, of course, but this trivial patch 
might help show the basic idea)

		Linus

---
diff --git a/cache.h b/cache.h
index bdbe2d6..7adc2e6 100644
--- a/cache.h
+++ b/cache.h
@@ -91,6 +91,7 @@ struct cache_entry {
 #define CE_NAMEMASK  (0x0fff)
 #define CE_STAGEMASK (0x3000)
 #define CE_UPDATE    (0x4000)
+#define CE_VALID     (0x8000)
 #define CE_STAGESHIFT 12
 
 #define create_ce_flags(len, stage) htons((len) | ((stage) << CE_STAGESHIFT))
diff --git a/read-cache.c b/read-cache.c
index c5474d4..738fe78 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -148,7 +148,16 @@ static int ce_match_stat_basic(struct ca
 
 int ce_match_stat(struct cache_entry *ce, struct stat *st)
 {
-	unsigned int changed = ce_match_stat_basic(ce, st);
+	unsigned int changed;
+
+	/*
+	 * If it's marked as always valid in the index, it's 
+	 * valid whatever the checked-out copy says
+	 */
+	if (ce->ce_flags & htons(CE_VALID))
+		return 0;
+
+	changed = ce_match_stat_basic(ce, st);
 
 	/*
 	 * Within 1 second of this sequence: