Instrumentation for an in-kernel getcwd() implementation.

Not yet activated. Diff by marius@ long ago, from NetBSD.
Okay miod@ and krw@.

2 files changed, 562 insertions, 1 deletions

diff --git a/sys/kern/syscalls.master b/sys/kern/syscalls.master
index 5e231f2975c..623b21011e3 100644
--- a/sys/kern/syscalls.master
+++ b/sys/kern/syscalls.master
@@ -1,4 +1,4 @@
-;	$OpenBSD: syscalls.master,v 1.81 2005/12/30 04:02:17 tedu Exp $
+;	$OpenBSD: syscalls.master,v 1.82 2006/04/28 08:34:31 pedro Exp $
 ;	$NetBSD: syscalls.master,v 1.32 1996/04/23 10:24:21 mycroft Exp $
 
 ;	@(#)syscalls.master	8.2 (Berkeley) 1/13/94
@@ -608,3 +608,4 @@
 302	UNIMPL
 303	UNIMPL
 #endif
+304	STD		{ int sys___getcwd(char *buf, size_t len); }
diff --git a/sys/kern/vfs_getcwd.c b/sys/kern/vfs_getcwd.c
new file mode 100644
index 00000000000..a4c81329801
--- /dev/null
+++ b/sys/kern/vfs_getcwd.c
@@ -0,0 +1,560 @@
+/* $OpenBSD: vfs_getcwd.c,v 1.1 2006/04/28 08:34:31 pedro Exp $ */
+/* $NetBSD: vfs_getcwd.c,v 1.3.2.3 1999/07/11 10:24:09 sommerfeld Exp $ */
+
+/*
+ * Copyright (c) 1999 The NetBSD Foundation, Inc.
+ * All rights reserved.
+ *
+ * This code is derived from software contributed to The NetBSD Foundation
+ * by Bill Sommerfeld.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. All advertising materials mentioning features or use of this software
+ *    must display the following acknowledgement:
+ *        This product includes software developed by the NetBSD
+ *        Foundation, Inc. and its contributors.
+ * 4. Neither the name of The NetBSD Foundation nor the names of its
+ *    contributors may be used to endorse or promote products derived
+ *    from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
+ * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
+ * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+ * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
+ * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+#include <sys/param.h>
+#include <sys/systm.h>
+#include <sys/namei.h>
+#include <sys/filedesc.h>
+#include <sys/kernel.h>
+#include <sys/file.h>
+#include <sys/stat.h>
+#include <sys/vnode.h>
+#include <sys/mount.h>
+#include <sys/proc.h>
+#include <sys/uio.h>
+#include <sys/malloc.h>
+#include <sys/dirent.h>
+#include <ufs/ufs/dir.h>	/* XXX only for DIRBLKSIZ */
+
+#include <sys/syscallargs.h>
+
+static int getcwd_scandir(struct vnode **, struct vnode **,
+    char **, char *, struct proc *);
+static int getcwd_getcache(struct vnode **, struct vnode **, char **, char *);
+static int getcwd_common(struct vnode *, struct vnode *,
+    char **, char *, int, int, struct proc *);
+
+static int vn_isunder(struct vnode *, struct vnode *, struct proc *);
+
+#define DIRENT_MINSIZE (sizeof(struct dirent) - (MAXNAMLEN+1) + 4)
+
+/*
+ * Vnode variable naming conventions in this file:
+ *
+ * rvp: the current root we're aiming towards.
+ * lvp, *lvpp: the "lower" vnode
+ * uvp, *uvpp: the "upper" vnode.
+ *
+ * Since all the vnodes we're dealing with are directories, and the
+ * lookups are going *up* in the filesystem rather than *down*, the
+ * usual "pvp" (parent) or "dvp" (directory) naming conventions are
+ * too confusing.
+ */
+
+/*
+ * XXX: is EINVAL the right thing to return if a directory is
+ *      malformed?
+ */
+
+
+/*
+ * Find parent vnode of *lvpp, return in *uvpp
+ *
+ * If we care about the name, scan it looking for name of directory
+ * entry pointing at lvp.
+ *
+ * Place the name in the buffer which starts at bufp, immediately
+ * before *bpp, and move bpp backwards to point at the start of it.
+ *
+ * On entry, *lvpp is a locked vnode reference; on exit, it is vput and NULL'ed
+ * On exit, *uvpp is either NULL or is a locked vnode reference.
+ */
+static int
+getcwd_scandir(struct vnode **lvpp, struct vnode **uvpp,
+    char **bpp, char *bufp, struct proc *p)
+{
+	int     error = 0;
+	int     eofflag;
+	off_t   off;
+	int     tries;
+	struct uio uio;
+	struct iovec iov;
+	char   *dirbuf = NULL;
+	int	dirbuflen;
+	ino_t   fileno;
+	struct vattr va;
+	struct vnode *uvp = NULL;
+	struct vnode *lvp = *lvpp;	
+	struct componentname cn;
+	int len, reclen;
+	tries = 0;
+
+	/*
+	 * If we want the filename, get some info we need while the
+	 * current directory is still locked.
+	 */
+	if (bufp != NULL) {
+		error = VOP_GETATTR(lvp, &va, p->p_ucred, p);
+		if (error) {
+			vput(lvp);
+			*lvpp = NULL;
+			*uvpp = NULL;
+			return error;
+		}
+	}
+
+	/*
+	 * Ok, we have to do it the hard way..
+	 * Next, get parent vnode using lookup of ..
+	 */
+	cn.cn_nameiop = LOOKUP;
+	cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
+	cn.cn_proc = p;
+	cn.cn_cred = p->p_ucred;
+	cn.cn_pnbuf = NULL;
+	cn.cn_nameptr = "..";
+	cn.cn_namelen = 2;
+	cn.cn_hash = 0;
+	cn.cn_consume = 0;
+	
+	/*
+	 * At this point, lvp is locked and will be unlocked by the lookup.
+	 * On successful return, *uvpp will be locked
+	 */
+	error = VOP_LOOKUP(lvp, uvpp, &cn);
+	if (error) {
+		vput(lvp);
+		*lvpp = NULL;
+		*uvpp = NULL;
+		return error;
+	}
+	uvp = *uvpp;
+
+	/* If we don't care about the pathname, we're done */
+	if (bufp == NULL) {
+		vrele(lvp);
+		*lvpp = NULL;
+		return 0;
+	}
+	
+	fileno = va.va_fileid;
+
+	dirbuflen = DIRBLKSIZ;
+	if (dirbuflen < va.va_blocksize)
+		dirbuflen = va.va_blocksize;
+	dirbuf = (char *)malloc(dirbuflen, M_TEMP, M_WAITOK);
+
+	off = 0;
+	do {
+		char   *cpos;
+		struct dirent *dp;
+
+		/* call VOP_READDIR of parent */
+		iov.iov_base = dirbuf;
+		iov.iov_len = dirbuflen;
+
+		uio.uio_iov = &iov;
+		uio.uio_iovcnt = 1;
+		uio.uio_offset = off;
+		uio.uio_resid = dirbuflen;
+		uio.uio_segflg = UIO_SYSSPACE;
+		uio.uio_rw = UIO_READ;
+		uio.uio_procp = p;
+
+		eofflag = 0;
+
+		error = VOP_READDIR(uvp, &uio, p->p_ucred, &eofflag, 0, 0);
+
+		off = uio.uio_offset;
+
+		/*
+		 * Try again if NFS tosses its cookies.
+		 */
+		if (error == EINVAL && tries < 3) {
+			tries++;
+			off = 0;
+			continue;
+		} else if (error != 0) {
+			/*
+			 * We simply bail on error, even if we don't
+			 * have eofflag yet.  This is the exact
+			 * behavior of the old userland getcwd()
+			 */
+			goto out;
+		}
+
+		/* No error */
+		cpos = dirbuf;
+		tries = 0;
+
+		/* scan directory page looking for matching vnode */ 
+		for (len = (dirbuflen - uio.uio_resid); len > 0;
+		     len -= reclen) {
+			dp = (struct dirent *)cpos;
+			reclen = dp->d_reclen;
+
+			/* check for malformed directory.. */
+			if (reclen < DIRENT_MINSIZE) {
+				error = EINVAL;
+				goto out;
+			}
+			/*
+			 * XXX should perhaps do VOP_LOOKUP to
+			 * check that we got back to the right place,
+			 * but getting the locking games for that
+			 * right would be heinous.
+			 */
+			if (dp->d_fileno == fileno) {
+				char *bp = *bpp;
+				bp -= dp->d_namlen;
+
+				if (bp <= bufp) {
+					error = ERANGE;
+					goto out;
+				}
+				bcopy(dp->d_name, bp, dp->d_namlen);
+				error = 0;
+				*bpp = bp;
+				goto out;
+			}
+			cpos += reclen;
+		}
+
+	} while (!eofflag);
+
+	error = ENOENT;
+
+out:
+	vrele(lvp);
+	*lvpp = NULL;
+	free(dirbuf, M_TEMP);
+	return error;
+}
+
+/*
+ * Look in the vnode-to-name reverse cache to see if
+ * we can find things the easy way.
+ *
+ * XXX vget failure path is untested.
+ *
+ * On entry, *lvpp is a locked vnode reference.
+ * On exit, one of the following is the case:
+ *	0) Both *lvpp and *uvpp are NULL and failure is returned.
+ * 	1) *uvpp is NULL, *lvpp remains locked and -1 is returned (cache miss)
+ *      2) *uvpp is a locked vnode reference, *lvpp is vput and NULL'ed
+ *	   and 0 is returned (cache hit)
+ */
+
+static int
+getcwd_getcache(struct vnode **lvpp, struct vnode **uvpp,
+    char **bpp, char *bufp)
+{
+	struct vnode *lvp, *uvp = NULL;
+	int error;
+	int vpid;
+	struct proc *p = curproc;
+	
+	lvp = *lvpp;
+
+	/*
+	 * This returns 0 on a cache hit, -1 on a clean cache miss, or
+	 * an errno on other failure.
+	 */
+	error = cache_revlookup(lvp, uvpp, bpp, bufp);
+	if (error) {
+		if (error != -1) {
+			vput(lvp);
+			*lvpp = NULL;
+			*uvpp = NULL;
+		}
+		return error;
+	}
+	uvp = *uvpp;
+	vpid = uvp->v_id;
+
+	/*
+	 * Since we're going up, we have to release the current lock
+	 * before we take the parent lock.
+	 */
+
+	VOP_UNLOCK(lvp, 0, p);
+
+	error = vget(uvp, LK_EXCLUSIVE | LK_RETRY, p);
+	if (error != 0)
+		*uvpp = NULL;
+	/*
+	 * Verify that vget succeeded, and check that vnode capability
+	 * didn't change while we were waiting for the lock.
+	 *
+	 * XXX: this is kind of nasty to have to check here.  It
+	 * should really be done in cache_revlookup() (see comments
+	 * there, too).
+	 */
+	if (error || (vpid != uvp->v_id)) {
+		/*
+		 * Oops, we missed.  If the vget failed, or the
+		 * capability changed, try to get our lock back; if
+		 * that works, tell caller to try things the hard way,
+		 * otherwise give up.
+		 */
+		if (!error)
+			vput(uvp);
+		*uvpp = NULL;
+		
+		error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY, p);
+
+		if (!error)
+			return -1;
+	}
+	vrele(lvp);
+	*lvpp = NULL;
+	return (error);
+}
+
+/*
+ * common routine shared by sys___getcwd() and vn_isunder()
+ */
+
+#define GETCWD_CHECK_ACCESS 0x0001
+
+static int
+getcwd_common(struct vnode *lvp, struct vnode *rvp,
+    char **bpp, char *bufp, int limit, int flags, struct proc *p)
+{
+	struct filedesc *fdp = p->p_fd;
+	struct vnode *uvp = NULL;
+	char *bp = NULL;
+	int error;
+	int perms = VEXEC;
+
+	if (rvp == NULL) {
+		rvp = fdp->fd_rdir;
+		if (rvp == NULL)
+			rvp = rootvnode;
+	}
+
+	VREF(rvp);
+	VREF(lvp);
+
+	/*
+	 * Error handling invariant:
+	 * Before a `goto out':
+	 *	lvp is either NULL, or locked and held.
+	 *	uvp is either NULL, or locked and held.
+	 */
+
+	error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY, p);
+	if (error) {
+		vrele(lvp);
+		lvp = NULL;
+		goto out;
+	}
+	if (bufp)
+		bp = *bpp;
+	/*
+	 * this loop will terminate when one of the following happens:
+	 *	- we hit the root
+	 *	- getdirentries or lookup fails
+	 *	- we run out of space in the buffer.
+	 */
+	if (lvp == rvp) {
+		if (bp)
+			*(--bp) = '/';
+		goto out;
+	}
+	do {
+		if (lvp->v_type != VDIR) {
+			error = ENOTDIR;
+			goto out;
+		}
+		
+		/*
+		 * access check here is optional, depending on
+		 * whether or not caller cares.
+		 */
+		if (flags & GETCWD_CHECK_ACCESS) {
+			error = VOP_ACCESS(lvp, perms, p->p_ucred, p);
+			if (error)
+				goto out;
+			perms = VEXEC|VREAD;
+		}
+		
+		/*
+		 * step up if we're a covered vnode..
+		 */
+		while (lvp->v_flag & VROOT) {
+			struct vnode *tvp;
+
+			if (lvp == rvp)
+				goto out;
+			
+			tvp = lvp;
+			lvp = lvp->v_mount->mnt_vnodecovered;
+			vput(tvp);
+			/*
+			 * hodie natus est radici frater
+			 */
+			if (lvp == NULL) {
+				error = ENOENT;
+				goto out;
+			}
+			VREF(lvp);
+			error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY, p);
+			if (error != 0) {
+				vrele(lvp);
+				lvp = NULL;
+				goto out;
+			}
+		}
+		/*
+		 * Look in the name cache; if that fails, look in the
+		 * directory..
+		 */
+		error = getcwd_getcache(&lvp, &uvp, &bp, bufp);
+		if (error == -1)
+			error = getcwd_scandir(&lvp, &uvp, &bp, bufp, p);
+		if (error)
+			goto out;
+#ifdef DIAGNOSTIC		
+		if (lvp != NULL)
+			panic("getcwd: oops, forgot to null lvp");
+		if (bufp && (bp <= bufp)) {
+			panic("getcwd: oops, went back too far");
+		}
+#endif		
+		if (bp)
+			*(--bp) = '/';
+		lvp = uvp;
+		uvp = NULL;
+		limit--;
+	} while ((lvp != rvp) && (limit > 0)); 
+
+out:
+	if (bpp)
+		*bpp = bp;
+	if (uvp)
+		vput(uvp);
+	if (lvp)
+		vput(lvp);
+	vrele(rvp);
+	return error;
+}
+
+/*
+ * Check if one directory can be found inside another in the directory
+ * hierarchy.
+ *
+ * Intended to be used in chroot, chdir, fchdir, etc., to ensure that
+ * chroot() actually means something.
+ */
+static int
+vn_isunder(struct vnode *lvp, struct vnode *rvp, struct proc *p)
+{
+	int error;
+
+	error = getcwd_common(lvp, rvp, NULL, NULL, MAXPATHLEN/2, 0, p);
+
+	if (!error)
+		return 1;
+	else
+		return 0;
+}
+
+/*
+ * Returns true if proc p1's root directory equal to or under p2's
+ * root directory.
+ *
+ * Intended to be used from ptrace/procfs sorts of things.
+ */
+
+int
+proc_isunder(struct proc *p1, struct proc *p2)
+{
+	struct vnode *r1 = p1->p_fd->fd_rdir;
+	struct vnode *r2 = p2->p_fd->fd_rdir;
+
+	if (r1 == NULL)
+		return (r2 == NULL);
+	else if (r2 == NULL)
+		return 1;
+	else
+		return vn_isunder(r1, r2, p2);
+}
+
+/*
+ * Find pathname of process's current directory.
+ *
+ * Use vfs vnode-to-name reverse cache; if that fails, fall back
+ * to reading directory contents.
+ */
+
+int
+sys___getcwd(struct proc *p, void *v, register_t *retval) 
+{
+	register struct sys___getcwd_args /* {
+		syscallarg(char *) buf;
+		syscallarg(size_t) len;
+	} */ *uap = v;
+
+	int     error;
+	char   *path;
+	char   *bp, *bend;
+	int     len = SCARG(uap, len);
+	int	lenused;
+
+	if (len > MAXPATHLEN*4)
+		len = MAXPATHLEN*4;
+	else if (len < 2)
+		return ERANGE;
+
+	path = (char *)malloc(len, M_TEMP, M_WAITOK);
+
+	bp = &path[len];
+	bend = bp;
+	*(--bp) = '\0';
+
+	/*
+	 * 5th argument here is "max number of vnodes to traverse".
+	 * Since each entry takes up at least 2 bytes in the output
+	 * buffer, limit it to N/2 vnodes for an N byte buffer.
+	 */
+	error = getcwd_common(p->p_fd->fd_cdir, NULL, &bp, path, len/2,
+	    GETCWD_CHECK_ACCESS, p);
+
+	if (error)
+		goto out;
+	lenused = bend - bp;
+	*retval = lenused;
+	/* put the result into user buffer */
+	error = copyout(bp, SCARG(uap, buf), lenused);
+
+out:
+	free(path, M_TEMP);
+	return error;
+}