venti: add bootstrap mode (write + no index)

R=rsc, rsc
http://codereview.appspot.com/6097047

src/cmd/venti/srv/dat.h

@@ -740,6 +740,7 @@ extern	Stats		stats;
 extern	u8int		zeroscore[VtScoreSize];
 extern	int		compressblocks;
 extern	int		writestodevnull;	/* dangerous - for performance debugging */
+extern	int		bootstrap;		/* writes but does not index - cannot read */
 extern	int		collectstats;
 extern	QLock	memdrawlock;
 extern	int		icachesleeptime;

src/cmd/venti/srv/httpd.c

@@ -396,6 +396,7 @@ static struct
 	"ignorebloom",	&ignorebloom,
 	"syncwrites",	&syncwrites,
 	"icacheprefetch",	&icacheprefetch,
+	"bootstrap",	&bootstrap,
 	0
 };
 

src/cmd/venti/srv/icache.c

@@ -387,6 +387,9 @@ icachelookup(u8int score[VtScoreSize], int type, IAddr *ia)
 {
 	IEntry *ie;
 
+	if(bootstrap)
+		return -1;
+
 	qlock(&icache.lock);
 	addstat(StatIcacheLookup, 1);
 	if((ie = ihashlookup(icache.hash, score, type)) != nil){
@@ -417,6 +420,9 @@ insertscore(u8int score[VtScoreSize], IAddr *ia, int state, AState *as)
 {
 	ISum *toload;
 
+	if(bootstrap)
+		return -1;
+
 	qlock(&icache.lock);
 	icacheinsert(score, ia, state);
 	if(state == IEClean)

src/cmd/venti/srv/lump.c

@@ -2,6 +2,7 @@
 #include "dat.h"
 #include "fns.h"
 
+int			bootstrap = 0;
 int			syncwrites = 0;
 int			queuewrites = 0;
 int			writestodevnull = 0;