Eliminate code duplication in vn_fullpath1() around the cache lookups

and calls to vn_vptocnp() by moving more of the common code to
vn_vptocnp(). Rename vn_vptocnp() to vn_vptocnp_locked() to signify that
cache is locked around the call.

Do not track buffer position by both the pointer and offset, use only
buflen to record the start of the free space.

Export vn_vptocnp() for external consumers as a wrapper around
vn_vptocnp_locked() that locks the cache and handles hold counts.

Tested by:	pho

1 files changed, 75 insertions, 85 deletions

diff --git a/sys/kern/vfs_cache.c b/sys/kern/vfs_cache.c
index 01c5e4c..cdfb308 100644
--- a/sys/kern/vfs_cache.c
+++ b/sys/kern/vfs_cache.c
@@ -206,7 +206,7 @@ SYSCTL_OPAQUE(_vfs_cache, OID_AUTO, nchstats, CTLFLAG_RD | CTLFLAG_MPSAFE,
 
 
 static void cache_zap(struct namecache *ncp);
-static int vn_vptocnp(struct vnode **vp, char **bp, char *buf, u_int *buflen);
+static int vn_vptocnp_locked(struct vnode **vp, char *buf, u_int *buflen);
 static int vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
     char *buf, char **retbuf, u_int buflen);
 
@@ -1036,12 +1036,55 @@ vn_fullpath_global(struct thread *td, struct vnode *vn,
 	return (error);
 }
 
+int
+vn_vptocnp(struct vnode **vp, char *buf, u_int *buflen)
+{
+	int error;
+
+	CACHE_RLOCK();
+	error = vn_vptocnp_locked(vp, buf, buflen);
+	if (error == 0) {
+		/*
+		 * vn_vptocnp_locked() dropped hold acquired by
+		 * VOP_VPTOCNP immediately after locking the
+		 * cache. Since we are going to drop the cache rlock,
+		 * re-hold the result.
+		 */
+		vhold(*vp);
+		CACHE_RUNLOCK();
+	}
+	return (error);
+}
+
 static int
-vn_vptocnp(struct vnode **vp, char **bp, char *buf, u_int *buflen)
+vn_vptocnp_locked(struct vnode **vp, char *buf, u_int *buflen)
 {
 	struct vnode *dvp;
+	struct namecache *ncp;
 	int error, vfslocked;
 
+	TAILQ_FOREACH(ncp, &((*vp)->v_cache_dst), nc_dst) {
+		if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
+			break;
+	}
+	if (ncp != NULL) {
+		if (*buflen < ncp->nc_nlen) {
+			CACHE_RUNLOCK();
+			numfullpathfail4++;
+			error = ENOMEM;
+			SDT_PROBE(vfs, namecache, fullpath, return, error,
+			    startvp, NULL, 0, 0);
+			return (error);
+		}
+		*buflen -= ncp->nc_nlen;
+		memcpy(buf + *buflen, ncp->nc_name, ncp->nc_nlen);
+		SDT_PROBE(vfs, namecache, fullpath, hit, ncp->nc_dvp,
+		    ncp->nc_name, vp, 0, 0);
+		*vp = ncp->nc_dvp;
+		return (0);
+	}
+	SDT_PROBE(vfs, namecache, fullpath, miss, vp, 0, 0, 0, 0);
+
 	vhold(*vp);
 	CACHE_RUNLOCK();
 	vfslocked = VFS_LOCK_GIANT((*vp)->v_mount);
@@ -1052,16 +1095,21 @@ vn_vptocnp(struct vnode **vp, char **bp, char *buf, u_int *buflen)
 	VFS_UNLOCK_GIANT(vfslocked);
 	if (error) {
 		numfullpathfail2++;
+		SDT_PROBE(vfs, namecache, fullpath, return,  error, startvp,
+		    NULL, 0, 0);
 		return (error);
 	}
-	*bp = buf + *buflen;
+
 	*vp = dvp;
 	CACHE_RLOCK();
 	if ((*vp)->v_iflag & VI_DOOMED) {
 		/* forced unmount */
 		CACHE_RUNLOCK();
 		vdrop(*vp);
-		return (ENOENT);
+		error = ENOENT;
+		SDT_PROBE(vfs, namecache, fullpath, return, error, startvp,
+		    NULL, 0, 0);
+		return (error);
 	}
 	vdrop(*vp);
 
@@ -1075,59 +1123,26 @@ static int
 vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
     char *buf, char **retbuf, u_int buflen)
 {
-	char *bp;
-	int error, i, slash_prefixed;
-	struct namecache *ncp;
+	int error, slash_prefixed;
 #ifdef KDTRACE_HOOKS
 	struct vnode *startvp = vp;
 #endif
 
 	buflen--;
-	bp = buf + buflen;
-	*bp = '\0';
+	buf[buflen] = '\0';
 	error = 0;
 	slash_prefixed = 0;
 
 	SDT_PROBE(vfs, namecache, fullpath, entry, vp, 0, 0, 0, 0);
-	CACHE_RLOCK();
 	numfullpathcalls++;
+	CACHE_RLOCK();
 	if (vp->v_type != VDIR) {
-		ncp = TAILQ_FIRST(&vp->v_cache_dst);
-		if (ncp != NULL) {
-			buflen -= ncp->nc_nlen;
-			for (i = ncp->nc_nlen - 1; i >= 0 && bp != buf; i--)
-				*--bp = ncp->nc_name[i];
-			if (bp == buf) {
-				numfullpathfail4++;
-				CACHE_RUNLOCK();
-				error = ENOMEM;
-				SDT_PROBE(vfs, namecache, fullpath, return,
-				    error, startvp, NULL, 0, 0);
-				return (error);
-			}
-			SDT_PROBE(vfs, namecache, fullpath, hit, ncp->nc_dvp,
-			    ncp->nc_name, vp, 0, 0);
-			vp = ncp->nc_dvp;
-		} else {
-			SDT_PROBE(vfs, namecache, fullpath, miss, vp, 0, 0,
-			    0, 0);
-			error = vn_vptocnp(&vp, &bp, buf, &buflen);
-			if (error) {
-				SDT_PROBE(vfs, namecache, fullpath, return,
-				    error, startvp, NULL, 0, 0);
-				return (error);
-			}
-		}
-		if (buflen <= 0) {
-			numfullpathfail4++;
-			CACHE_RUNLOCK();
-			error = ENOMEM;
-			SDT_PROBE(vfs, namecache, fullpath, return, error,
-			    startvp, NULL, 0, 0);
+		error = vn_vptocnp_locked(&vp, buf, &buflen);
+		if (error)
 			return (error);
-		}
-		*--bp = '/';
-		buflen--;
+		if (buflen == 0)
+			return (ENOMEM);
+		buf[--buflen] = '/';
 		slash_prefixed = 1;
 	}
 	while (vp != rdir && vp != rootvnode) {
@@ -1141,64 +1156,39 @@ vn_fullpath1(struct thread *td, struct vnode *vp, struct vnode *rdir,
 			continue;
 		}
 		if (vp->v_type != VDIR) {
-			numfullpathfail1++;
 			CACHE_RUNLOCK();
+			numfullpathfail1++;
 			error = ENOTDIR;
 			break;
 		}
- 		TAILQ_FOREACH(ncp, &vp->v_cache_dst, nc_dst)
- 			if ((ncp->nc_flag & NCF_ISDOTDOT) == 0)
- 				break;
-		if (ncp != NULL) {
-			buflen -= ncp->nc_nlen;
-			for (i = ncp->nc_nlen - 1; i >= 0 && bp != buf; i--)
-				*--bp = ncp->nc_name[i];
-			if (bp == buf) {
-				numfullpathfail4++;
-				CACHE_RUNLOCK();
-				error = ENOMEM;
-				break;
-			}
-			SDT_PROBE(vfs, namecache, fullpath, hit, ncp->nc_dvp,
-			    ncp->nc_name, vp, 0, 0);
-			vp = ncp->nc_dvp;
-		} else {
-			SDT_PROBE(vfs, namecache, fullpath, miss, vp, 0, 0,
-			    0, 0);
-			error = vn_vptocnp(&vp, &bp, buf, &buflen);
-			if (error)
-				break;
-		}
-		if (buflen <= 0) {
-			numfullpathfail4++;
-			CACHE_RUNLOCK();
+		error = vn_vptocnp_locked(&vp, buf, &buflen);
+		if (error)
+			break;
+		if (buflen == 0) {
 			error = ENOMEM;
 			break;
 		}
-		*--bp = '/';
-		buflen--;
+		buf[--buflen] = '/';
 		slash_prefixed = 1;
 	}
-	if (error) {
-		SDT_PROBE(vfs, namecache, fullpath, return, error, startvp,
-		    NULL, 0, 0);
+	if (error)
 		return (error);
-	}
 	if (!slash_prefixed) {
-		if (bp == buf) {
-			numfullpathfail4++;
+		if (buflen == 0) {
 			CACHE_RUNLOCK();
+			numfullpathfail4++;
 			SDT_PROBE(vfs, namecache, fullpath, return, 0,
-			    startvp, bp, 0, 0);
+			    startvp, fullpath, 0, 0);
 			return (ENOMEM);
-		} else
-			*--bp = '/';
+		}
+		buf[--buflen] = '/';
 	}
 	numfullpathfound++;
 	CACHE_RUNLOCK();
 
-	SDT_PROBE(vfs, namecache, fullpath, return, 0, startvp, bp, 0, 0);
-	*retbuf = bp;
+	SDT_PROBE(vfs, namecache, fullpath, return, 0, startvp, buf + *buflen,
+	    0, 0);
+	*retbuf = buf + buflen;
 	return (0);
 }