kernel: pipelined read ahead for the mount cache

this changes devmnt adding mntrahread() function and some helpers
for it to do pipelined sequential read ahead for the mount cache.

basically, cread() calls mntrahread() with Mntrah structure and it
figures out if we where reading sequentially and if thats the case
issues reads of c->iounit size in advance.

the read ahead state (Mntrah) is kept in the mount cache so we can
handle (read ahead) cache invalidation in the presence of writes.

1 files changed, 26 insertions, 0 deletions

diff --git a/sys/src/9/port/portdat.h b/sys/src/9/port/portdat.h
index 106f016f8..16f24a10d 100644
--- a/sys/src/9/port/portdat.h
+++ b/sys/src/9/port/portdat.h
@@ -16,7 +16,9 @@ typedef struct Log	Log;
 typedef struct Logflag	Logflag;
 typedef struct Mntcache Mntcache;
 typedef struct Mount	Mount;
+typedef struct Mntrah	Mntrah;
 typedef struct Mntrpc	Mntrpc;
+typedef struct Mntproc	Mntproc;
 typedef struct Mnt	Mnt;
 typedef struct Mhead	Mhead;
 typedef struct Note	Note;
@@ -270,6 +272,29 @@ struct Mhead
 	Mhead*	hash;			/* Hash chain */
 };
 
+struct Mntrah
+{
+	Rendez;
+
+	ulong	vers;
+
+	vlong	off;
+	vlong	seq;
+
+	uint	i;
+	Mntrpc	*r[8];
+};
+
+struct Mntproc
+{
+	Rendez;
+
+	Mnt	*m;
+	Mntrpc	*r;
+	void	*a;
+	void	(*f)(Mntrpc*, void*);
+};
+
 struct Mnt
 {
 	Lock;
@@ -277,6 +302,7 @@ struct Mnt
 	Chan	*c;		/* Channel to file service */
 	Proc	*rip;		/* Reader in progress */
 	Mntrpc	*queue;		/* Queue of pending requests on this channel */
+	Mntproc	defered[8];	/* Worker processes for defered RPCs (read ahead) */
 	ulong	id;		/* Multiplexer id for channel check */
 	Mnt	*list;		/* Free list */
 	int	flags;		/* cache */