Add dev_strategy_csw() function, which is similar to dev_strategy()

but assumes that a thread reference was already obtained on the passed
device.  Use the function from physio(), to avoid two extra dev_mtx
lock and unlock.  Note that physio() is always used as the cdevsw
method, or is called from a cdevsw method, and the caller already owns
the reference.

dev_strategy() is left to keep KPI intact, but now it is implemented
as a wrapper around dev_strategy_csw().

Do some style cleanup in physio().

Requested and reviewed by:	kan (previous version)
Sponsored by:	The FreeBSD Foundation
MFC after:	2 weeks

3 files changed, 32 insertions, 23 deletions

diff --git a/sys/kern/kern_physio.c b/sys/kern/kern_physio.c
index 1eb5b8f..1387c8e 100644
--- a/sys/kern/kern_physio.c
+++ b/sys/kern/kern_physio.c
@@ -34,11 +34,11 @@ __FBSDID("$FreeBSD$");
 int
 physio(struct cdev *dev, struct uio *uio, int ioflag)
 {
-	int i;
-	int error;
+	struct buf *bp;
+	struct cdevsw *csw;
 	caddr_t sa;
 	u_int iolen;
-	struct buf *bp;
+	int error, i, mapped;
 
 	/* Keep the process UPAGES from being swapped. XXX: why ? */
 	PHOLD(curproc);
@@ -91,11 +91,8 @@ physio(struct cdev *dev, struct uio *uio, int ioflag)
 
 			bp->b_blkno = btodb(bp->b_offset);
 
+			csw = dev->si_devsw;
 			if (uio->uio_segflg == UIO_USERSPACE) {
-				struct cdevsw *csw;
-				int mapped;
-
-				csw = dev->si_devsw;
 				if (csw != NULL &&
                                     (csw->d_flags & D_UNMAPPED_IO) != 0)
 					mapped = 0;
@@ -107,7 +104,7 @@ physio(struct cdev *dev, struct uio *uio, int ioflag)
 				}
 			}
 
-			dev_strategy(dev, bp);
+			dev_strategy_csw(dev, csw, bp);
 			if (uio->uio_rw == UIO_READ)
 				bwait(bp, PRIBIO, "physrd");
 			else
diff --git a/sys/kern/vfs_bio.c b/sys/kern/vfs_bio.c
index 7b1aa8e..db7d681 100644
--- a/sys/kern/vfs_bio.c
+++ b/sys/kern/vfs_bio.c
@@ -3687,11 +3687,34 @@ void
 dev_strategy(struct cdev *dev, struct buf *bp)
 {
 	struct cdevsw *csw;
-	struct bio *bip;
 	int ref;
 
-	if ((!bp->b_iocmd) || (bp->b_iocmd & (bp->b_iocmd - 1)))
-		panic("b_iocmd botch");
+	KASSERT(dev->si_refcount > 0,
+	    ("dev_strategy on un-referenced struct cdev *(%s) %p",
+	    devtoname(dev), dev));
+
+	csw = dev_refthread(dev, &ref);
+	dev_strategy_csw(dev, csw, bp);
+	dev_relthread(dev, ref);
+}
+
+void
+dev_strategy_csw(struct cdev *dev, struct cdevsw *csw, struct buf *bp)
+{
+	struct bio *bip;
+
+	KASSERT(bp->b_iocmd == BIO_READ || bp->b_iocmd == BIO_WRITE,
+	    ("b_iocmd botch"));
+	KASSERT(((dev->si_flags & SI_ETERNAL) != 0 && csw != NULL) ||
+	    dev->si_threadcount > 0,
+	    ("dev_strategy_csw threadcount cdev *(%s) %p", devtoname(dev),
+	    dev));
+	if (csw == NULL) {
+		bp->b_error = ENXIO;
+		bp->b_ioflags = BIO_ERROR;
+		bufdone(bp);
+		return;
+	}
 	for (;;) {
 		bip = g_new_bio();
 		if (bip != NULL)
@@ -3707,19 +3730,7 @@ dev_strategy(struct cdev *dev, struct buf *bp)
 	bip->bio_done = bufdonebio;
 	bip->bio_caller2 = bp;
 	bip->bio_dev = dev;
-	KASSERT(dev->si_refcount > 0,
-	    ("dev_strategy on un-referenced struct cdev *(%s)",
-	    devtoname(dev)));
-	csw = dev_refthread(dev, &ref);
-	if (csw == NULL) {
-		g_destroy_bio(bip);
-		bp->b_error = ENXIO;
-		bp->b_ioflags = BIO_ERROR;
-		bufdone(bp);
-		return;
-	}
 	(*csw->d_strategy)(bip);
-	dev_relthread(dev, ref);
 }
 
 /*
diff --git a/sys/sys/conf.h b/sys/sys/conf.h
index 8d53839..5a579b4 100644
--- a/sys/sys/conf.h
+++ b/sys/sys/conf.h
@@ -255,6 +255,7 @@ void	dev_ref(struct cdev *dev);
 void	dev_refl(struct cdev *dev);
 void	dev_rel(struct cdev *dev);
 void	dev_strategy(struct cdev *dev, struct buf *bp);
+void	dev_strategy_csw(struct cdev *dev, struct cdevsw *csw, struct buf *bp);
 struct cdev *make_dev(struct cdevsw *_devsw, int _unit, uid_t _uid, gid_t _gid,
 		int _perms, const char *_fmt, ...) __printflike(6, 7);
 struct cdev *make_dev_cred(struct cdevsw *_devsw, int _unit,