Implement VFS read clustering for MSDOSFS

This is the reverted commit by mpi@ from msdosfs_vnops.c 1.105 plus some
additional tweaks to fix some cluster/block number confusion that lead
to regressions when seeking past the end of a file.

The original commit message was:

  The logic used in msdosfs_bmap() to loop calling pcbmap() comes from
  FreeBSD and is not really efficient but it is good enough since it is
  only called when generating I/O.

  With this diff I get a 100% improvement when reading big files from a
  crappy USB stick.

  With this and bread_cluster(9) modified to not re-fetch B_CACHED buffers,
  reading large contiguous files with chunk sizes of MAXPHYS is almost as
  fast as physio(9) on the same device.

  For a 'real world' example, when copying music files from a USB stick I
  see a speed jump from 15MB/s on -current to 24Mb/s with this diff.

  While here rename some 'lbn' variables into 'cn' to better reflect what
  we're dealing with.

  Tested by Mathieu, with support from deraadt@

ok mpi@

2 files changed, 67 insertions, 44 deletions

diff --git a/sys/msdosfs/denode.h b/sys/msdosfs/denode.h
index cdca90500ab..efa8192a06d 100644
--- a/sys/msdosfs/denode.h
+++ b/sys/msdosfs/denode.h
@@ -1,4 +1,4 @@
-/*	$OpenBSD: denode.h,v 1.30 2016/08/30 19:47:23 sf Exp $	*/
+/*	$OpenBSD: denode.h,v 1.31 2017/05/29 13:48:12 sf Exp $	*/
 /*	$NetBSD: denode.h,v 1.24 1997/10/17 11:23:39 ws Exp $	*/
 
 /*-
@@ -142,7 +142,6 @@ struct denode {
 	struct vnode *de_devvp;	/* vnode of blk dev we live on */
 	uint32_t de_flag;		/* flag bits */
 	dev_t de_dev;		/* device where direntry lives */
-	daddr_t de_lastr;
 	uint32_t de_dirclust;	/* cluster of the directory file containing this entry */
 	uint32_t de_diroffset;	/* offset of this entry in the directory cluster */
 	uint32_t de_fndoffset;	/* offset of found dir entry */
diff --git a/sys/msdosfs/msdosfs_vnops.c b/sys/msdosfs/msdosfs_vnops.c
index 39c60044df5..61b45af6185 100644
--- a/sys/msdosfs/msdosfs_vnops.c
+++ b/sys/msdosfs/msdosfs_vnops.c
@@ -1,4 +1,4 @@
-/*	$OpenBSD: msdosfs_vnops.c,v 1.113 2016/08/30 19:47:23 sf Exp $	*/
+/*	$OpenBSD: msdosfs_vnops.c,v 1.114 2017/05/29 13:48:12 sf Exp $	*/
 /*	$NetBSD: msdosfs_vnops.c,v 1.63 1997/10/17 11:24:19 ws Exp $	*/
 
 /*-
@@ -77,13 +77,13 @@
 
 static uint32_t fileidhash(uint64_t);
 
+int msdosfs_bmaparray(struct vnode *, daddr_t, daddr_t *, int *);
 int msdosfs_kqfilter(void *);
 int filt_msdosfsread(struct knote *, long);
 int filt_msdosfswrite(struct knote *, long);
 int filt_msdosfsvnode(struct knote *, long);
 void filt_msdosfsdetach(struct knote *);
 
-
 /*
  * Some general notes:
  *
@@ -509,18 +509,14 @@ int
 msdosfs_read(void *v)
 {
 	struct vop_read_args *ap = v;
-	int error = 0;
-	uint32_t diff;
-	int blsize;
-	int isadir;
-	uint32_t n;
-	long on;
-	daddr_t lbn, rablock, rablkno;
-	struct buf *bp;
 	struct vnode *vp = ap->a_vp;
 	struct denode *dep = VTODE(vp);
 	struct msdosfsmount *pmp = dep->de_pmp;
 	struct uio *uio = ap->a_uio;
+	int isadir, error = 0;
+	uint32_t n, diff, size, on;
+	struct buf *bp;
+	daddr_t cn, bn;
 
 	/*
 	 * If they didn't ask for any data, then we are done.
@@ -535,7 +531,8 @@ msdosfs_read(void *v)
 		if (uio->uio_offset >= dep->de_FileSize)
 			return (0);
 
-		lbn = de_cluster(pmp, uio->uio_offset);
+		cn = de_cluster(pmp, uio->uio_offset);
+		size = pmp->pm_bpcluster;
 		on = uio->uio_offset & pmp->pm_crbomask;
 		n = ulmin(pmp->pm_bpcluster - on, uio->uio_resid);
 
@@ -548,31 +545,22 @@ msdosfs_read(void *v)
 		if (diff < n)
 			n = diff;
 
-		/* convert cluster # to block # if a directory */
-		if (isadir) {
-			error = pcbmap(dep, lbn, &lbn, 0, &blsize);
-			if (error)
-				return (error);
-		}
 		/*
 		 * If we are operating on a directory file then be sure to
 		 * do i/o with the vnode for the filesystem instead of the
 		 * vnode for the directory.
 		 */
 		if (isadir) {
-			error = bread(pmp->pm_devvp, lbn, blsize, &bp);
+			error = pcbmap(dep, cn, &cn, 0, &size);
+			if (error)
+				return (error);
+			error = bread(pmp->pm_devvp, cn, size, &bp);
 		} else {
-			rablock = lbn + 1;
-			rablkno = de_cn2bn(pmp, rablock);
-			if (dep->de_lastr + 1 == lbn &&
-			    de_cn2off(pmp, rablock) < dep->de_FileSize)
-				error = breadn(vp, de_cn2bn(pmp, lbn),
-				    pmp->pm_bpcluster, &rablkno,
-				    &pmp->pm_bpcluster, 1, &bp);
+			bn = de_cn2bn(pmp, cn);
+			if (de_cn2off(pmp, cn + 1) >= dep->de_FileSize)
+				error = bread(vp, bn, size, &bp);
 			else
-				error = bread(vp, de_cn2bn(pmp, lbn),
-				    pmp->pm_bpcluster, &bp);
-			dep->de_lastr = lbn;
+				error = bread_cluster(vp, bn, size, &bp);
 		}
 		n = min(n, pmp->pm_bpcluster - bp->b_resid);
 		if (error) {
@@ -601,7 +589,7 @@ msdosfs_write(void *v)
 	uint32_t osize;
 	int error = 0;
 	uint32_t count, lastcn;
-	daddr_t bn;
+	daddr_t cn, bn;
 	struct buf *bp;
 	int ioflag = ap->a_ioflag;
 	struct uio *uio = ap->a_uio;
@@ -678,20 +666,23 @@ msdosfs_write(void *v)
 		lastcn = de_clcount(pmp, osize) - 1;
 
 	do {
-		if (de_cluster(pmp, uio->uio_offset) > lastcn) {
+		croffset = uio->uio_offset & pmp->pm_crbomask;
+		cn = de_cluster(pmp, uio->uio_offset);
+
+		if (cn > lastcn) {
 			error = ENOSPC;
 			break;
 		}
 
-		bn = de_blk(pmp, uio->uio_offset);
-		if ((uio->uio_offset & pmp->pm_crbomask) == 0
-		    && (de_blk(pmp, uio->uio_offset + uio->uio_resid) > de_blk(pmp, uio->uio_offset)
-			|| uio->uio_offset + uio->uio_resid >= dep->de_FileSize)) {
+		if (croffset == 0 &&
+		    (de_cluster(pmp, uio->uio_offset + uio->uio_resid) > cn ||
+		     (uio->uio_offset + uio->uio_resid) >= dep->de_FileSize)) {
 			/*
 			 * If either the whole cluster gets written,
 			 * or we write the cluster from its start beyond EOF,
 			 * then no need to read data from disk.
 			 */
+			bn = de_cn2bn(pmp, cn);
 			bp = getblk(thisvp, bn, pmp->pm_bpcluster, 0, 0);
 			clrbuf(bp);
 			/*
@@ -713,8 +704,10 @@ msdosfs_write(void *v)
 			}
 		} else {
 			/*
-			 * The block we need to write into exists, so read it in.
+			 * The block we need to write into exists, so
+			 * read it in.
 			 */
+			bn = de_cn2bn(pmp, cn);
 			error = bread(thisvp, bn, pmp->pm_bpcluster, &bp);
 			if (error) {
 				brelse(bp);
@@ -722,7 +715,6 @@ msdosfs_write(void *v)
 			}
 		}
 
-		croffset = uio->uio_offset & pmp->pm_crbomask;
 		n = ulmin(uio->uio_resid, pmp->pm_bpcluster - croffset);
 		if (uio->uio_offset + n > dep->de_FileSize) {
 			dep->de_FileSize = uio->uio_offset + n;
@@ -1755,7 +1747,7 @@ msdosfs_islocked(void *v)
 
 /*
  * vp  - address of vnode file the file
- * bn  - which cluster we are interested in mapping to a filesystem block number.
+ * bn  - which cluster we are interested in mapping to a filesystem block number
  * vpp - returns the vnode for the block special file holding the filesystem
  *	 containing the file of interest
  * bnp - address of where to return the filesystem relative block number
@@ -1765,19 +1757,51 @@ msdosfs_bmap(void *v)
 {
 	struct vop_bmap_args *ap = v;
 	struct denode *dep = VTODE(ap->a_vp);
-	struct msdosfsmount *pmp = dep->de_pmp;
 
 	if (ap->a_vpp != NULL)
 		*ap->a_vpp = dep->de_devvp;
 	if (ap->a_bnp == NULL)
 		return (0);
-	if (ap->a_runp) {
+
+	return (msdosfs_bmaparray(ap->a_vp, ap->a_bn, ap->a_bnp, ap->a_runp));
+}
+
+int
+msdosfs_bmaparray(struct vnode *vp, daddr_t cn, daddr_t *bnp, int *runp)
+{
+	struct denode *dep = VTODE(vp);
+	struct msdosfsmount *pmp = dep->de_pmp;
+	struct mount *mp;
+	int error, maxrun = 0, run;
+	daddr_t daddr;
+
+	mp = vp->v_mount;
+
+	if (runp) {
 		/*
-		 * Sequential clusters should be counted here.
+		 * XXX
+		 * If MAXBSIZE is the largest transfer the disks can handle,
+		 * we probably want maxrun to be 1 block less so that we
+		 * don't create a block larger than the device can handle.
 		 */
-		*ap->a_runp = 0;
+		*runp = 0;
+		maxrun = min(MAXBSIZE / mp->mnt_stat.f_iosize - 1,
+		    pmp->pm_maxcluster - cn);
 	}
-	return (pcbmap(dep, de_bn2cn(pmp, ap->a_bn), ap->a_bnp, 0, 0));
+
+	if ((error = pcbmap(dep, cn, bnp, 0, 0)) != 0)
+		return (error);
+
+	for (run = 1; run <= maxrun; run++) {
+		error = pcbmap(dep, cn + run, &daddr, 0, 0);
+		if (error != 0 || (daddr != *bnp + de_cn2bn(pmp, run)))
+			break;
+	}
+
+	if (runp)
+		*runp = run - 1;
+
+	return (0);
 }
 
 int