The Design and Implementation of the FreeBSD Operating System, Second Edition
Now available: The Design and Implementation of the FreeBSD Operating System (Second Edition)


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FreeBSD/Linux Kernel Cross Reference
sys/compat/linux/linux_getcwd.c

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    1 /* $OpenBSD: linux_getcwd.c,v 1.2 2001/05/16 12:50:21 ho Exp $ */
    2 /* $NetBSD: vfs_getcwd.c,v 1.3.2.3 1999/07/11 10:24:09 sommerfeld Exp $ */
    3 /*-
    4  * Copyright (c) 1999 The NetBSD Foundation, Inc.
    5  * All rights reserved.
    6  *
    7  * This code is derived from software contributed to The NetBSD Foundation
    8  * by Bill Sommerfeld.
    9  *
   10  * Redistribution and use in source and binary forms, with or without
   11  * modification, are permitted provided that the following conditions
   12  * are met:
   13  * 1. Redistributions of source code must retain the above copyright
   14  *    notice, this list of conditions and the following disclaimer.
   15  * 2. Redistributions in binary form must reproduce the above copyright
   16  *    notice, this list of conditions and the following disclaimer in the
   17  *    documentation and/or other materials provided with the distribution.
   18  * 3. All advertising materials mentioning features or use of this software
   19  *    must display the following acknowledgement:
   20  *        This product includes software developed by the NetBSD
   21  *        Foundation, Inc. and its contributors.
   22  * 4. Neither the name of The NetBSD Foundation nor the names of its
   23  *    contributors may be used to endorse or promote products derived
   24  *    from this software without specific prior written permission.
   25  *
   26  * THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
   27  * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
   28  * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
   29  * PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
   30  * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
   31  * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
   32  * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
   33  * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
   34  * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
   35  * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   36  * POSSIBILITY OF SUCH DAMAGE.
   37  */
   38 
   39 #include <sys/cdefs.h>
   40 __FBSDID("$FreeBSD: releng/5.2/sys/compat/linux/linux_getcwd.c 122861 2003-11-17 18:57:20Z rwatson $");
   41 
   42 #include "opt_compat.h"
   43 #include "opt_mac.h"
   44 
   45 #include <sys/param.h>
   46 #include <sys/systm.h>
   47 #include <sys/namei.h>
   48 #include <sys/filedesc.h>
   49 #include <sys/kernel.h>
   50 #include <sys/file.h>
   51 #include <sys/stat.h>
   52 #include <sys/syscallsubr.h>
   53 #include <sys/vnode.h>
   54 #include <sys/mount.h>
   55 #include <sys/proc.h>
   56 #include <sys/uio.h>
   57 #include <sys/mac.h>
   58 #include <sys/malloc.h>
   59 #include <sys/dirent.h>
   60 #include <ufs/ufs/dir.h>        /* XXX only for DIRBLKSIZ */
   61 
   62 #include <machine/../linux/linux.h>
   63 #include <machine/../linux/linux_proto.h>
   64 #include <compat/linux/linux_util.h>
   65 
   66 static int
   67 linux_getcwd_scandir(struct vnode **, struct vnode **,
   68     char **, char *, struct thread *);
   69 static int
   70 linux_getcwd_common(struct vnode *, struct vnode *,
   71                    char **, char *, int, int, struct thread *);
   72 
   73 #define DIRENT_MINSIZE (sizeof(struct dirent) - (MAXNAMLEN+1) + 4)
   74 
   75 /*
   76  * Vnode variable naming conventions in this file:
   77  *
   78  * rvp: the current root we're aiming towards.
   79  * lvp, *lvpp: the "lower" vnode
   80  * uvp, *uvpp: the "upper" vnode.
   81  *
   82  * Since all the vnodes we're dealing with are directories, and the
   83  * lookups are going *up* in the filesystem rather than *down*, the
   84  * usual "pvp" (parent) or "dvp" (directory) naming conventions are
   85  * too confusing.
   86  */
   87 
   88 /*
   89  * XXX Will infinite loop in certain cases if a directory read reliably
   90  *      returns EINVAL on last block.
   91  * XXX is EINVAL the right thing to return if a directory is malformed?
   92  */
   93 
   94 /*
   95  * XXX Untested vs. mount -o union; probably does the wrong thing.
   96  */
   97 
   98 /*
   99  * Find parent vnode of *lvpp, return in *uvpp
  100  *
  101  * If we care about the name, scan it looking for name of directory
  102  * entry pointing at lvp.
  103  *
  104  * Place the name in the buffer which starts at bufp, immediately
  105  * before *bpp, and move bpp backwards to point at the start of it.
  106  *
  107  * On entry, *lvpp is a locked vnode reference; on exit, it is vput and NULL'ed
  108  * On exit, *uvpp is either NULL or is a locked vnode reference.
  109  */
  110 static int
  111 linux_getcwd_scandir(lvpp, uvpp, bpp, bufp, td)
  112         struct vnode **lvpp;
  113         struct vnode **uvpp;
  114         char **bpp;
  115         char *bufp;
  116         struct thread *td;
  117 {
  118         int     error = 0;
  119         int     eofflag;
  120         off_t   off;
  121         int     tries;
  122         struct uio uio;
  123         struct iovec iov;
  124         char   *dirbuf = NULL;
  125         int     dirbuflen;
  126         ino_t   fileno;
  127         struct vattr va;
  128         struct vnode *uvp = NULL;
  129         struct vnode *lvp = *lvpp;      
  130         struct componentname cn;
  131         int len, reclen;
  132         tries = 0;
  133 
  134         /*
  135          * If we want the filename, get some info we need while the
  136          * current directory is still locked.
  137          */
  138         if (bufp != NULL) {
  139                 error = VOP_GETATTR(lvp, &va, td->td_ucred, td);
  140                 if (error) {
  141                         vput(lvp);
  142                         *lvpp = NULL;
  143                         *uvpp = NULL;
  144                         return error;
  145                 }
  146         }
  147 
  148         /*
  149          * Ok, we have to do it the hard way..
  150          * Next, get parent vnode using lookup of ..
  151          */
  152         cn.cn_nameiop = LOOKUP;
  153         cn.cn_flags = ISLASTCN | ISDOTDOT | RDONLY;
  154         cn.cn_thread = td;
  155         cn.cn_cred = td->td_ucred;
  156         cn.cn_pnbuf = NULL;
  157         cn.cn_nameptr = "..";
  158         cn.cn_namelen = 2;
  159         cn.cn_consume = 0;
  160         
  161         /*
  162          * At this point, lvp is locked and will be unlocked by the lookup.
  163          * On successful return, *uvpp will be locked
  164          */
  165 #ifdef MAC
  166         error = mac_check_vnode_lookup(td->td_ucred, lvp, &cn);
  167         if (error == 0)
  168 #endif
  169                 error = VOP_LOOKUP(lvp, uvpp, &cn);
  170         if (error) {
  171                 vput(lvp);
  172                 *lvpp = NULL;
  173                 *uvpp = NULL;
  174                 return error;
  175         }
  176         uvp = *uvpp;
  177 
  178         /* If we don't care about the pathname, we're done */
  179         if (bufp == NULL) {
  180                 vrele(lvp);
  181                 *lvpp = NULL;
  182                 return 0;
  183         }
  184         
  185         fileno = va.va_fileid;
  186 
  187         dirbuflen = DIRBLKSIZ;
  188         if (dirbuflen < va.va_blocksize)
  189                 dirbuflen = va.va_blocksize;
  190         dirbuf = (char *)malloc(dirbuflen, M_TEMP, M_WAITOK);
  191 
  192 #if 0
  193 unionread:
  194 #endif
  195         off = 0;
  196         do {
  197                 /* call VOP_READDIR of parent */
  198                 iov.iov_base = dirbuf;
  199                 iov.iov_len = dirbuflen;
  200 
  201                 uio.uio_iov = &iov;
  202                 uio.uio_iovcnt = 1;
  203                 uio.uio_offset = off;
  204                 uio.uio_resid = dirbuflen;
  205                 uio.uio_segflg = UIO_SYSSPACE;
  206                 uio.uio_rw = UIO_READ;
  207                 uio.uio_td = td;
  208 
  209                 eofflag = 0;
  210 
  211 #ifdef MAC
  212                 error = mac_check_vnode_readdir(td->td_ucred, uvp);
  213                 if (error == 0)
  214 #endif /* MAC */
  215                         error = VOP_READDIR(uvp, &uio, td->td_ucred, &eofflag,
  216                             0, 0);
  217 
  218                 off = uio.uio_offset;
  219 
  220                 /*
  221                  * Try again if NFS tosses its cookies.
  222                  * XXX this can still loop forever if the directory is busted
  223                  * such that the second or subsequent page of it always
  224                  * returns EINVAL
  225                  */
  226                 if ((error == EINVAL) && (tries < 3)) {
  227                         off = 0;
  228                         tries++;
  229                         continue;       /* once more, with feeling */
  230                 }
  231 
  232                 if (!error) {
  233                         char   *cpos;
  234                         struct dirent *dp;
  235                         
  236                         cpos = dirbuf;
  237                         tries = 0;
  238                                 
  239                         /* scan directory page looking for matching vnode */ 
  240                         for (len = (dirbuflen - uio.uio_resid); len > 0; len -= reclen) {
  241                                 dp = (struct dirent *) cpos;
  242                                 reclen = dp->d_reclen;
  243 
  244                                 /* check for malformed directory.. */
  245                                 if (reclen < DIRENT_MINSIZE) {
  246                                         error = EINVAL;
  247                                         goto out;
  248                                 }
  249                                 /*
  250                                  * XXX should perhaps do VOP_LOOKUP to
  251                                  * check that we got back to the right place,
  252                                  * but getting the locking games for that
  253                                  * right would be heinous.
  254                                  */
  255                                 if ((dp->d_type != DT_WHT) &&
  256                                     (dp->d_fileno == fileno)) {
  257                                         char *bp = *bpp;
  258                                         bp -= dp->d_namlen;
  259                                         
  260                                         if (bp <= bufp) {
  261                                                 error = ERANGE;
  262                                                 goto out;
  263                                         }
  264                                         bcopy(dp->d_name, bp, dp->d_namlen);
  265                                         error = 0;
  266                                         *bpp = bp;
  267                                         goto out;
  268                                 }
  269                                 cpos += reclen;
  270                         }
  271                 }
  272         } while (!eofflag);
  273         error = ENOENT;
  274                 
  275 out:
  276         vrele(lvp);
  277         *lvpp = NULL;
  278         free(dirbuf, M_TEMP);
  279         return error;
  280 }
  281 
  282 
  283 /*
  284  * common routine shared by sys___getcwd() and linux_vn_isunder()
  285  */
  286 
  287 #define GETCWD_CHECK_ACCESS 0x0001
  288 
  289 static int
  290 linux_getcwd_common (lvp, rvp, bpp, bufp, limit, flags, td)
  291         struct vnode *lvp;
  292         struct vnode *rvp;
  293         char **bpp;
  294         char *bufp;
  295         int limit;
  296         int flags;
  297         struct thread *td;
  298 {
  299         struct filedesc *fdp = td->td_proc->p_fd;
  300         struct vnode *uvp = NULL;
  301         char *bp = NULL;
  302         int error;
  303         int perms = VEXEC;
  304 
  305         if (rvp == NULL) {
  306                 rvp = fdp->fd_rdir;
  307                 if (rvp == NULL)
  308                         rvp = rootvnode;
  309         }
  310         
  311         VREF(rvp);
  312         VREF(lvp);
  313 
  314         /*
  315          * Error handling invariant:
  316          * Before a `goto out':
  317          *      lvp is either NULL, or locked and held.
  318          *      uvp is either NULL, or locked and held.
  319          */
  320 
  321         error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY, td);
  322         if (error) {
  323                 vrele(lvp);
  324                 lvp = NULL;
  325                 goto out;
  326         }
  327         if (bufp)
  328                 bp = *bpp;
  329         /*
  330          * this loop will terminate when one of the following happens:
  331          *      - we hit the root
  332          *      - getdirentries or lookup fails
  333          *      - we run out of space in the buffer.
  334          */
  335         if (lvp == rvp) {
  336                 if (bp)
  337                         *(--bp) = '/';
  338                 goto out;
  339         }
  340         do {
  341                 if (lvp->v_type != VDIR) {
  342                         error = ENOTDIR;
  343                         goto out;
  344                 }
  345                 
  346                 /*
  347                  * access check here is optional, depending on
  348                  * whether or not caller cares.
  349                  */
  350                 if (flags & GETCWD_CHECK_ACCESS) {
  351                         error = VOP_ACCESS(lvp, perms, td->td_ucred, td);
  352                         if (error)
  353                                 goto out;
  354                         perms = VEXEC|VREAD;
  355                 }
  356                 
  357                 /*
  358                  * step up if we're a covered vnode..
  359                  */
  360                 while (lvp->v_vflag & VV_ROOT) {
  361                         struct vnode *tvp;
  362 
  363                         if (lvp == rvp)
  364                                 goto out;
  365                         
  366                         tvp = lvp;
  367                         lvp = lvp->v_mount->mnt_vnodecovered;
  368                         vput(tvp);
  369                         /*
  370                          * hodie natus est radici frater
  371                          */
  372                         if (lvp == NULL) {
  373                                 error = ENOENT;
  374                                 goto out;
  375                         }
  376                         VREF(lvp);
  377                         error = vn_lock(lvp, LK_EXCLUSIVE | LK_RETRY, td);
  378                         if (error != 0) {
  379                                 vrele(lvp);
  380                                 lvp = NULL;
  381                                 goto out;
  382                         }
  383                 }
  384                 error = linux_getcwd_scandir(&lvp, &uvp, &bp, bufp, td);
  385                 if (error)
  386                         goto out;
  387 #if DIAGNOSTIC          
  388                 if (lvp != NULL)
  389                         panic("getcwd: oops, forgot to null lvp");
  390                 if (bufp && (bp <= bufp)) {
  391                         panic("getcwd: oops, went back too far");
  392                 }
  393 #endif          
  394                 if (bp) 
  395                         *(--bp) = '/';
  396                 lvp = uvp;
  397                 uvp = NULL;
  398                 limit--;
  399         } while ((lvp != rvp) && (limit > 0)); 
  400 
  401 out:
  402         if (bpp)
  403                 *bpp = bp;
  404         if (uvp)
  405                 vput(uvp);
  406         if (lvp)
  407                 vput(lvp);
  408         vrele(rvp);
  409         return error;
  410 }
  411 
  412 
  413 /*
  414  * Find pathname of process's current directory.
  415  *
  416  * Use vfs vnode-to-name reverse cache; if that fails, fall back
  417  * to reading directory contents.
  418  */
  419 
  420 int
  421 linux_getcwd(struct thread *td, struct linux_getcwd_args *args)
  422 {
  423         caddr_t bp, bend, path;
  424         int error, len, lenused;
  425 
  426 #ifdef DEBUG
  427         printf("Linux-emul(%ld): getcwd(%p, %ld)\n", (long)td->td_proc->p_pid,
  428                args->buf, (long)args->bufsize);
  429 #endif
  430 
  431         len = args->bufsize;
  432 
  433         if (len > MAXPATHLEN*4)
  434                 len = MAXPATHLEN*4;
  435         else if (len < 2)
  436                 return ERANGE;
  437 
  438         path = (char *)malloc(len, M_TEMP, M_WAITOK);
  439 
  440         error = kern___getcwd(td, path, UIO_SYSSPACE, len);
  441         if (!error) {
  442                 lenused = strlen(path) + 1;
  443                 if (lenused <= args->bufsize) {
  444                         td->td_retval[0] = lenused;
  445                         error = copyout(path, args->buf, lenused);
  446                 }
  447                 else
  448                         error = ERANGE;
  449         } else {
  450                 bp = &path[len];
  451                 bend = bp;
  452                 *(--bp) = '\0';
  453 
  454                 /*
  455                  * 5th argument here is "max number of vnodes to traverse".
  456                  * Since each entry takes up at least 2 bytes in the output buffer,
  457                  * limit it to N/2 vnodes for an N byte buffer.
  458                  */
  459 
  460                 error = linux_getcwd_common (td->td_proc->p_fd->fd_cdir, NULL,
  461                     &bp, path, len/2, GETCWD_CHECK_ACCESS, td);
  462 
  463                 if (error)
  464                         goto out;
  465                 lenused = bend - bp;
  466                 td->td_retval[0] = lenused;
  467                 /* put the result into user buffer */
  468                 error = copyout(bp, args->buf, lenused);
  469         }
  470 out:
  471         free(path, M_TEMP);
  472         return (error);
  473 }
  474 

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