CLEANUP: fd: remove unused cb->b pointers in the struct fdtab

These pointers were used to hold pointers to buffers in the past, but
since we introduced the stream interface, they're no longer used but
they were still sometimes set.

Removing them shrink the struct fdtab from 32 to 24 bytes on 32-bit machines,
and from 52 to 36 bytes on 64-bit machines, which is a significant saving. A
quick tests shows a steady 0.5% performance gain, probably due to the better
cache efficiency.

include/types/fd.h

@@ -69,7 +69,6 @@ enum {
 struct fdtab {
 	struct {
 		int (*f)(int fd);            /* read/write function */
-		struct buffer *b;            /* read/write buffer */
 	} cb[DIR_SIZE];
 	void *owner;                         /* the session (or proxy) associated with this fd */
 	struct {                             /* used by pollers which support speculative polling */

src/checks.c

@@ -1434,9 +1434,7 @@ static struct task *process_chk(struct task *t)
 						fd_insert(fd);
 						fdtab[fd].owner = t;
 						fdtab[fd].cb[DIR_RD].f = &event_srv_chk_r;
-						fdtab[fd].cb[DIR_RD].b = NULL;
 						fdtab[fd].cb[DIR_WR].f = &event_srv_chk_w;
-						fdtab[fd].cb[DIR_WR].b = NULL;
 						fdinfo[fd].peeraddr = (struct sockaddr *)&sa;
 						fdinfo[fd].peerlen = get_addr_len(&sa);
 						fdtab[fd].state = FD_STCONN; /* connection in progress */

src/proto_tcp.c

@@ -451,8 +451,6 @@ int tcp_connect_server(struct stream_interface *si)
 	fdtab[fd].owner = si;
 	fdtab[fd].state = FD_STCONN; /* connection in progress */
 	fdtab[fd].flags = FD_FL_TCP | FD_FL_TCP_NODELAY;
-	fdtab[fd].cb[DIR_RD].b = si->ib;
-	fdtab[fd].cb[DIR_WR].b = si->ob;
 
 	/* If we have nothing to send or if we want to initialize the sock layer,
 	 * we want to confirm that the TCP connection is established before doing
@@ -755,7 +753,6 @@ int tcp_bind_listener(struct listener *listener, char *errmsg, int errlen)
 	fdtab[fd].flags = FD_FL_TCP | ((listener->options & LI_O_NOLINGER) ? FD_FL_TCP_NOLING : 0);
 	fdtab[fd].cb[DIR_RD].f = listener->proto->accept;
 	fdtab[fd].cb[DIR_WR].f = NULL; /* never called */
-	fdtab[fd].cb[DIR_RD].b = fdtab[fd].cb[DIR_WR].b = NULL;
 
 	fdinfo[fd].peeraddr = NULL;
 	fdinfo[fd].peerlen = 0;

src/proto_uxst.c

@@ -264,7 +264,6 @@ static int uxst_bind_listener(struct listener *listener, char *errmsg, int errle
 	fd_insert(fd);
 	fdtab[fd].cb[DIR_RD].f = listener->proto->accept;
 	fdtab[fd].cb[DIR_WR].f = NULL; /* never called */
-	fdtab[fd].cb[DIR_RD].b = fdtab[fd].cb[DIR_WR].b = NULL;
 	fdtab[fd].owner = listener; /* reference the listener instead of a task */
 	fdtab[fd].state = FD_STLISTEN;
 	fdinfo[fd].peeraddr = NULL;

src/session.c

@@ -284,9 +284,7 @@ int session_accept(struct listener *l, int cfd, struct sockaddr_storage *addr)
 	fdtab[cfd].state = FD_STREADY;
 	fdtab[cfd].flags = 0;
 	fdtab[cfd].cb[DIR_RD].f = s->si[0].sock.read;
-	fdtab[cfd].cb[DIR_RD].b = s->req;
 	fdtab[cfd].cb[DIR_WR].f = s->si[0].sock.write;
-	fdtab[cfd].cb[DIR_WR].b = s->rep;
 	fdinfo[cfd].peeraddr = (struct sockaddr *)&s->si[0].addr.from;
 	fdinfo[cfd].peerlen  = sizeof(s->si[0].addr.from);
 	EV_FD_SET(cfd, DIR_RD);