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      1 /*
      2  * CDDL HEADER START
      3  *
      4  * The contents of this file are subject to the terms of the
      5  * Common Development and Distribution License (the "License").
      6  * You may not use this file except in compliance with the License.
      7  *
      8  * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
      9  * or http://www.opensolaris.org/os/licensing.
     10  * See the License for the specific language governing permissions
     11  * and limitations under the License.
     12  *
     13  * When distributing Covered Code, include this CDDL HEADER in each
     14  * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
     15  * If applicable, add the following below this CDDL HEADER, with the
     16  * fields enclosed by brackets "[]" replaced with your own identifying
     17  * information: Portions Copyright [yyyy] [name of copyright owner]
     18  *
     19  * CDDL HEADER END
     20  */
     21 /*
     22  * Copyright 2007 Sun Microsystems, Inc.  All rights reserved.
     23  * Use is subject to license terms.
     24  */
     25 
     26 /*	Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T	*/
     27 /*	  All Rights Reserved  	*/
     28 
     29 /*
     30  * Portions of this source code were derived from Berkeley 4.3 BSD
     31  * under license from the Regents of the University of California.
     32  */
     33 
     34 #pragma ident	"%Z%%M%	%I%	%E% SMI"
     35 
     36 #include <sys/param.h>
     37 #include <sys/isa_defs.h>
     38 #include <sys/types.h>
     39 #include <sys/sysmacros.h>
     40 #include <sys/cred.h>
     41 #include <sys/systm.h>
     42 #include <sys/errno.h>
     43 #include <sys/pathname.h>
     44 #include <sys/vnode.h>
     45 #include <sys/file.h>
     46 #include <sys/uio.h>
     47 #include <sys/debug.h>
     48 #include <fs/fs_subr.h>
     49 
     50 /*
     51  * Read the contents of a symbolic link.
     52  */
     53 ssize_t
     54 readlink(char *name, char *buf, size_t count)
     55 {
     56 	vnode_t *vp;
     57 	struct iovec aiov;
     58 	struct uio auio;
     59 	int error;
     60 	struct vattr vattr;
     61 	ssize_t cnt;
     62 	int estale_retry = 0;
     63 
     64 	if ((cnt = (ssize_t)count) < 0)
     65 		return (set_errno(EINVAL));
     66 
     67 lookup:
     68 	if (error = lookupname(name, UIO_USERSPACE, NO_FOLLOW, NULLVPP, &vp)) {
     69 		if ((error == ESTALE) && fs_need_estale_retry(estale_retry++))
     70 			goto lookup;
     71 		return (set_errno(error));
     72 	}
     73 
     74 	if (vp->v_type != VLNK) {
     75 		/*
     76 		 * Ask the underlying filesystem if it wants this
     77 		 * object to look like a symlink at user-level.
     78 		 */
     79 		vattr.va_mask = AT_TYPE;
     80 		error = VOP_GETATTR(vp, &vattr, 0, CRED(), NULL);
     81 		if (error || vattr.va_type != VLNK) {
     82 			VN_RELE(vp);
     83 			if ((error == ESTALE) &&
     84 			    fs_need_estale_retry(estale_retry++))
     85 				goto lookup;
     86 			return (set_errno(EINVAL));
     87 		}
     88 	}
     89 	aiov.iov_base = buf;
     90 	aiov.iov_len = cnt;
     91 	auio.uio_iov = &aiov;
     92 	auio.uio_iovcnt = 1;
     93 	auio.uio_loffset = 0;
     94 	auio.uio_segflg = UIO_USERSPACE;
     95 	auio.uio_extflg = UIO_COPY_CACHED;
     96 	auio.uio_resid = cnt;
     97 	error = VOP_READLINK(vp, &auio, CRED(), NULL);
     98 	VN_RELE(vp);
     99 	if (error) {
    100 		if ((error == ESTALE) && fs_need_estale_retry(estale_retry++))
    101 			goto lookup;
    102 		return (set_errno(error));
    103 	}
    104 	return ((ssize_t)(cnt - auio.uio_resid));
    105 }
    106 
    107 #ifdef _SYSCALL32_IMPL
    108 /*
    109  * readlink32() intentionally returns a ssize_t rather than ssize32_t;
    110  * see the comments above read32 for details.
    111  */
    112 
    113 ssize_t
    114 readlink32(caddr32_t name, caddr32_t buf, size32_t count)
    115 {
    116 	return ((ssize32_t)readlink((char *)(uintptr_t)name,
    117 	    (char *)(uintptr_t)buf, (ssize32_t)count));
    118 }
    119 
    120 #endif	/* _SYSCALL32_IMPL */
    121