fd(4): replace disksort() with a bufq

[David Gwynne]

this replaces the bare use of disksort with a bufq in fd. this means
it will use the new system default of the nscan sorting algorithm,
but that shouldnt be a noticable change.

it works for me, but i would love to hear from someone with a real
floppy drive still...

ok?

Index: fd.c
===================================================================
RCS file: /cvs/src/sys/dev/isa/fd.c,v
retrieving revision 1.94
diff -u -p -r1.94 fd.c
--- fd.c        11 Jun 2013 16:42:15 -0000      1.94
+++ fd.c        31 Oct 2013 03:05:19 -0000
@@ -119,7 +119,8 @@ struct fd_softc {
 
        TAILQ_ENTRY(fd_softc) sc_drivechain;
        int sc_ops;             /* I/O ops since last switch */
-       struct buf sc_q;        /* head of buf chain */
+       struct bufq sc_bufq;    /* pending I/O */
+       struct buf *sc_bp;      /* the current I/O */
        struct timeout fd_motor_on_to;
        struct timeout fd_motor_off_to;
        struct timeout fdtimeout_to;
@@ -299,6 +300,7 @@ fdattach(struct device *parent, struct d
         */
        fd->sc_dk.dk_flags = DKF_NOLABELREAD;
        fd->sc_dk.dk_name = fd->sc_dev.dv_xname;
+       bufq_init(&fd->sc_bufq, BUFQ_DEFAULT);
        disk_attach(&fd->sc_dev, &fd->sc_dk);
 
        /* Setup timeout structures */
@@ -414,11 +416,13 @@ fdstrategy(struct buf *bp)
            bp->b_blkno, bp->b_bcount, fd->sc_blkno, bp->b_cylinder, sz);
 #endif
 
+       /* Queue I/O */
+       bufq_queue(&fd->sc_bufq, bp);
+
        /* Queue transfer on drive, activate drive and controller if idle. */
        s = splbio();
-       disksort(&fd->sc_q, bp);
        timeout_del(&fd->fd_motor_off_to); /* a good idea */
-       if (!fd->sc_q.b_active)
+       if (fd->sc_bp == NULL)
                fdstart(fd);
 #ifdef DIAGNOSTIC
        else {
@@ -449,7 +453,7 @@ fdstart(struct fd_softc *fd)
        int active = !TAILQ_EMPTY(&fdc->sc_link.fdlink.sc_drives);
 
        /* Link into controller queue. */
-       fd->sc_q.b_active = 1;
+       fd->sc_bp = bufq_dequeue(&fd->sc_bufq);
        TAILQ_INSERT_TAIL(&fdc->sc_link.fdlink.sc_drives, fd, sc_drivechain);
 
        /* If controller not already active, start it. */
@@ -464,6 +468,10 @@ fdfinish(struct fd_softc *fd, struct buf
 
        splassert(IPL_BIO);
 
+       bp->b_resid = fd->sc_bcount;
+       fd->sc_skip = 0;
+       fd->sc_bp = bufq_dequeue(&fd->sc_bufq);
+
        /*
         * Move this drive to the end of the queue to give others a `fair'
         * chance.  We only force a switch if N operations are completed while
@@ -473,15 +481,11 @@ fdfinish(struct fd_softc *fd, struct buf
        if (TAILQ_NEXT(fd, sc_drivechain) != NULL && ++fd->sc_ops >= 8) {
                fd->sc_ops = 0;
                TAILQ_REMOVE(&fdc->sc_link.fdlink.sc_drives, fd, sc_drivechain);
-               if (bp->b_actf) {
+               if (fd->sc_bp != NULL) {
                        TAILQ_INSERT_TAIL(&fdc->sc_link.fdlink.sc_drives, fd,
                                          sc_drivechain);
-               } else
-                       fd->sc_q.b_active = 0;
+               }
        }
-       bp->b_resid = fd->sc_bcount;
-       fd->sc_skip = 0;
-       fd->sc_q.b_actf = bp->b_actf;
 
        biodone(bp);
        /* turn off motor 5s from now */
@@ -661,11 +665,10 @@ loop:
        }
        fd_bsize = FD_BSIZE(fd);
 
-       bp = fd->sc_q.b_actf;
+       bp = fd->sc_bp;
        if (bp == NULL) {
                fd->sc_ops = 0;
                TAILQ_REMOVE(&fdc->sc_link.fdlink.sc_drives, fd, sc_drivechain);
-               fd->sc_q.b_active = 0;
                goto loop;
        }
 
@@ -927,7 +930,7 @@ fdtimeout(void *arg)
 #endif
        fdcstatus(&fd->sc_dev, 0, "timeout");
 
-       if (fd->sc_q.b_actf)
+       if (fd->sc_bp != NULL)
                fdc->sc_state++;
        else
                fdc->sc_state = DEVIDLE;
@@ -940,7 +943,7 @@ void
 fdretry(struct fd_softc *fd)
 {
        struct fdc_softc *fdc = (void *)fd->sc_dev.dv_parent;
-       struct buf *bp = fd->sc_q.b_actf;
+       struct buf *bp = fd->sc_bp;
 
        if (fd->sc_opts & FDOPT_NORETRY)
            goto fail;