9660srv: keep data and metadata separate in the cache with a tag

[plan9front.git] / sys / src / cmd / 9660srv / iobuf.c

diff --git a/sys/src/cmd/9660srv/iobuf.c b/sys/src/cmd/9660srv/iobuf.c
index 6bba533e8fec6e3465f8597641a9d20346656ee4..a617483e61862976dfe4a0ef8e7f576558a56190 100644 (file)
--- a/sys/src/cmd/9660srv/iobuf.c
+++ b/sys/src/cmd/9660srv/iobuf.c
@@ -31,7 +31,7 @@ int nclust = NCLUST;
 static Ioclust*        iohead;
 static Ioclust*        iotail;
 
-static Ioclust*        getclust(Xdata*, long);
+static Ioclust*        getclust(Xdata*, long, ulong);
 static void    putclust(Ioclust*);
 static void    xread(Ioclust*);
 
@@ -53,6 +53,16 @@ iobuf_init(void)
        for(i=0; i<nclust; i++){
                c = (Ioclust*)mem;
                mem += sizeof(Ioclust);
+
+               /*
+                * on a iso filesystem, data is usually layed out sequentially
+                * but directory information is at the end of the disk. to avoid
+                * evicting directory information when reading large sequential
+                * files, we keep them tagged in the cache. for now, we use
+                * an 8th of the clusters for meta data.
+                */
+               c->tag = i <= (nclust/8);
+
                c->addr = -1;
                c->prev = iotail;
                if(iotail)
@@ -87,13 +97,13 @@ purgebuf(Xdata *dev)
 }
 
 static Ioclust*
-getclust(Xdata *dev, long addr)
+getclust(Xdata *dev, long addr, ulong tag)
 {
        Ioclust *c, *f;
 
        f = nil;
        for(c=iohead; c; c=c->next){
-               if(!c->busy)
+               if(!c->busy && c->tag == tag)
                        f = c;
                if(c->addr == addr && c->dev == dev){
                        c->busy++;
@@ -141,13 +151,13 @@ putclust(Ioclust *c)
 }
 
 Iobuf*
-getbuf(Xdata *dev, ulong addr)
+getbuf(Xdata *dev, ulong addr, ulong tag)
 {
        int off;
        Ioclust *c;
 
        off = addr%BUFPERCLUST;
-       c = getclust(dev, addr - off);
+       c = getclust(dev, addr - off, tag);
        if(c->nbuf < off){
                c->busy--;
                error("I/O read error");