Re: kern/38643: [dM] st tape drive loses data

[der Mouse <mouse%Rodents-Montreal.ORG@localhost>]

Today, I tried adding printfs in stread and ststrategy.  These indicate
that, even when stread provides a buf, physio dispatches two requests
to the strategy routine:

stread: offset 0 resid 1048577
ststrategy: bcount 65536 blkno 0
ststrategy: bcount 65536 blkno 128
stread: offset 10240 resid 10240
ststrategy: bcount 10240 blkno 20

So it appears there is something wrong with physio.  After staring at
it for a while, I came up with this

--- /dev/fd/4   Tue Dec  9 16:18:08 2003
+++ /dev/fd/5   Tue Dec  9 16:18:08 2003
@@ -336,6 +336,9 @@
                        if (error) {
                                goto done_locked;
                        }
+                       if ((mbp->b_flags & B_ERROR) != 0) {
+                               goto done_locked;
+                       }
                        simple_unlock(&mbp->b_interlock);
                        if (obp != NULL) {
                                /*

which appears to fix this.  (Otherwise, the main physio line blocks in
physio_wait before the first request comes off the workqueue and sets
B_ERROR in mbp, and the B_ERROR isn't noticed until after dispatching
the second request.)  Combine this with making st.c use its own buffer
in stread and stwrite

--- /dev/fd/4   Tue Dec  9 16:18:08 2003
+++ /dev/fd/5   Tue Dec  9 16:18:08 2003
@@ -1379,8 +1379,9 @@
 stread(dev_t dev, struct uio *uio, int iomode)
 {
        struct st_softc *st = st_cd.cd_devs[STUNIT(dev)];
+       static struct buf buf;
 
-       return (physio(ststrategy, NULL, dev, B_READ,
+       return (physio(ststrategy, &buf, dev, B_READ,
            st->sc_periph->periph_channel->chan_adapter->adapt_minphys, uio));
 }
 
@@ -1388,8 +1389,9 @@
 stwrite(dev_t dev, struct uio *uio, int iomode)
 {
        struct st_softc *st = st_cd.cd_devs[STUNIT(dev)];
+       static struct buf buf;
 
-       return (physio(ststrategy, NULL, dev, B_WRITE,
+       return (physio(ststrategy, &buf, dev, B_WRITE,
            st->sc_periph->periph_channel->chan_adapter->adapt_minphys, uio));
 }
 

and, in initial tests, st is fine.  I'll have to run with this for a
while to see if there are any subtle problems remaining.

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