The Design and Implementation of the FreeBSD Operating System, Second Edition
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FreeBSD/Linux Kernel Cross Reference
sys/fs/ext2fs/ext2_bmap.c

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    1 /*-
    2  * Copyright (c) 1989, 1991, 1993
    3  *      The Regents of the University of California.  All rights reserved.
    4  * (c) UNIX System Laboratories, Inc.
    5  * All or some portions of this file are derived from material licensed
    6  * to the University of California by American Telephone and Telegraph
    7  * Co. or Unix System Laboratories, Inc. and are reproduced herein with
    8  * the permission of UNIX System Laboratories, Inc.
    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  * 4. Neither the name of the University nor the names of its contributors
   19  *    may be used to endorse or promote products derived from this software
   20  *    without specific prior written permission.
   21  *
   22  * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
   23  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   24  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   25  * ARE DISCLAIMED.  IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
   26  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   27  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   28  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   29  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   30  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   31  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   32  * SUCH DAMAGE.
   33  *
   34  *      @(#)ufs_bmap.c  8.7 (Berkeley) 3/21/95
   35  * $FreeBSD: releng/10.4/sys/fs/ext2fs/ext2_bmap.c 317532 2017-04-27 23:14:01Z pfg $
   36  */
   37 
   38 #include <sys/param.h>
   39 #include <sys/systm.h>
   40 #include <sys/bio.h>
   41 #include <sys/buf.h>
   42 #include <sys/proc.h>
   43 #include <sys/vnode.h>
   44 #include <sys/mount.h>
   45 #include <sys/resourcevar.h>
   46 #include <sys/stat.h>
   47 
   48 #include <fs/ext2fs/inode.h>
   49 #include <fs/ext2fs/fs.h>
   50 #include <fs/ext2fs/ext2fs.h>
   51 #include <fs/ext2fs/ext2_dinode.h>
   52 #include <fs/ext2fs/ext2_extern.h>
   53 #include <fs/ext2fs/ext2_mount.h>
   54 
   55 static int ext4_bmapext(struct vnode *, int32_t, int64_t *, int *, int *);
   56 
   57 /*
   58  * Bmap converts the logical block number of a file to its physical block
   59  * number on the disk. The conversion is done by using the logical block
   60  * number to index into the array of block pointers described by the dinode.
   61  */
   62 int
   63 ext2_bmap(struct vop_bmap_args *ap)
   64 {
   65         daddr_t blkno;
   66         int error;
   67 
   68         /*
   69          * Check for underlying vnode requests and ensure that logical
   70          * to physical mapping is requested.
   71          */
   72         if (ap->a_bop != NULL)
   73                 *ap->a_bop = &VTOI(ap->a_vp)->i_devvp->v_bufobj;
   74         if (ap->a_bnp == NULL)
   75                 return (0);
   76 
   77         if (VTOI(ap->a_vp)->i_flag & IN_E4EXTENTS)
   78                 error = ext4_bmapext(ap->a_vp, ap->a_bn, &blkno,
   79                     ap->a_runp, ap->a_runb);
   80         else
   81                 error = ext2_bmaparray(ap->a_vp, ap->a_bn, &blkno,
   82                     ap->a_runp, ap->a_runb);
   83         *ap->a_bnp = blkno;
   84         return (error);
   85 }
   86 
   87 /*
   88  * This function converts the logical block number of a file to
   89  * its physical block number on the disk within ext4 extents.
   90  */
   91 static int
   92 ext4_bmapext(struct vnode *vp, int32_t bn, int64_t *bnp, int *runp, int *runb)
   93 {
   94         struct inode *ip;
   95         struct m_ext2fs *fs;
   96         struct ext4_extent *ep;
   97         struct ext4_extent_path path = {.ep_bp = NULL};
   98         daddr_t lbn;
   99         int ret = 0;
  100 
  101         ip = VTOI(vp);
  102         fs = ip->i_e2fs;
  103         lbn = bn;
  104 
  105         /*
  106          * TODO: need to implement read ahead to improve the performance.
  107          */
  108         if (runp != NULL)
  109                 *runp = 0;
  110 
  111         if (runb != NULL)
  112                 *runb = 0;
  113 
  114         ext4_ext_find_extent(fs, ip, lbn, &path);
  115         ep = path.ep_ext;
  116         if (ep == NULL)
  117                 ret = EIO;
  118         else {
  119                 *bnp = fsbtodb(fs, lbn - ep->e_blk +
  120                     (ep->e_start_lo | (daddr_t)ep->e_start_hi << 32));
  121 
  122                 if (*bnp == 0)
  123                         *bnp = -1;
  124         }
  125 
  126         if (path.ep_bp != NULL) {
  127                 brelse(path.ep_bp);
  128                 path.ep_bp = NULL;
  129         }
  130 
  131         return (ret);
  132 }
  133 
  134 /*
  135  * Indirect blocks are now on the vnode for the file.  They are given negative
  136  * logical block numbers.  Indirect blocks are addressed by the negative
  137  * address of the first data block to which they point.  Double indirect blocks
  138  * are addressed by one less than the address of the first indirect block to
  139  * which they point.  Triple indirect blocks are addressed by one less than
  140  * the address of the first double indirect block to which they point.
  141  *
  142  * ext2_bmaparray does the bmap conversion, and if requested returns the
  143  * array of logical blocks which must be traversed to get to a block.
  144  * Each entry contains the offset into that block that gets you to the
  145  * next block and the disk address of the block (if it is assigned).
  146  */
  147 
  148 int
  149 ext2_bmaparray(struct vnode *vp, daddr_t bn, daddr_t *bnp, int *runp, int *runb)
  150 {
  151         struct inode *ip;
  152         struct buf *bp;
  153         struct ext2mount *ump;
  154         struct mount *mp;
  155         struct indir a[NIADDR + 1], *ap;
  156         daddr_t daddr;
  157         e2fs_lbn_t metalbn;
  158         int error, num, maxrun = 0, bsize;
  159         int *nump;
  160 
  161         ap = NULL;
  162         ip = VTOI(vp);
  163         mp = vp->v_mount;
  164         ump = VFSTOEXT2(mp);
  165 
  166         bsize = EXT2_BLOCK_SIZE(ump->um_e2fs);
  167 
  168         if (runp) {
  169                 maxrun = mp->mnt_iosize_max / bsize - 1;
  170                 *runp = 0;
  171         }
  172         if (runb)
  173                 *runb = 0;
  174 
  175 
  176         ap = a;
  177         nump = &num;
  178         error = ext2_getlbns(vp, bn, ap, nump);
  179         if (error)
  180                 return (error);
  181 
  182         num = *nump;
  183         if (num == 0) {
  184                 *bnp = blkptrtodb(ump, ip->i_db[bn]);
  185                 if (*bnp == 0) {
  186                         *bnp = -1;
  187                 } else if (runp) {
  188                         daddr_t bnb = bn;
  189 
  190                         for (++bn; bn < NDADDR && *runp < maxrun &&
  191                             is_sequential(ump, ip->i_db[bn - 1], ip->i_db[bn]);
  192                             ++bn, ++*runp);
  193                         bn = bnb;
  194                         if (runb && (bn > 0)) {
  195                                 for (--bn; (bn >= 0) && (*runb < maxrun) &&
  196                                         is_sequential(ump, ip->i_db[bn],
  197                                                 ip->i_db[bn + 1]);
  198                                                 --bn, ++*runb);
  199                         }
  200                 }
  201                 return (0);
  202         }
  203 
  204         /* Get disk address out of indirect block array */
  205         daddr = ip->i_ib[ap->in_off];
  206 
  207         for (bp = NULL, ++ap; --num; ++ap) {
  208                 /*
  209                  * Exit the loop if there is no disk address assigned yet and
  210                  * the indirect block isn't in the cache, or if we were
  211                  * looking for an indirect block and we've found it.
  212                  */
  213 
  214                 metalbn = ap->in_lbn;
  215                 if ((daddr == 0 && !incore(&vp->v_bufobj, metalbn)) || metalbn == bn)
  216                         break;
  217                 /*
  218                  * If we get here, we've either got the block in the cache
  219                  * or we have a disk address for it, go fetch it.
  220                  */
  221                 if (bp)
  222                         bqrelse(bp);
  223 
  224                 bp = getblk(vp, metalbn, bsize, 0, 0, 0);
  225                 if ((bp->b_flags & B_CACHE) == 0) {
  226 #ifdef INVARIANTS
  227                         if (!daddr)
  228                                 panic("ext2_bmaparray: indirect block not in cache");
  229 #endif
  230                         bp->b_blkno = blkptrtodb(ump, daddr);
  231                         bp->b_iocmd = BIO_READ;
  232                         bp->b_flags &= ~B_INVAL;
  233                         bp->b_ioflags &= ~BIO_ERROR;
  234                         vfs_busy_pages(bp, 0);
  235                         bp->b_iooffset = dbtob(bp->b_blkno);
  236                         bstrategy(bp);
  237                         curthread->td_ru.ru_inblock++;
  238                         error = bufwait(bp);
  239                         if (error) {
  240                                 brelse(bp);
  241                                 return (error);
  242                         }
  243                 }
  244 
  245                 daddr = ((e2fs_daddr_t *)bp->b_data)[ap->in_off];
  246                 if (num == 1 && daddr && runp) {
  247                         for (bn = ap->in_off + 1;
  248                             bn < MNINDIR(ump) && *runp < maxrun &&
  249                             is_sequential(ump,
  250                             ((e2fs_daddr_t *)bp->b_data)[bn - 1],
  251                             ((e2fs_daddr_t *)bp->b_data)[bn]);
  252                             ++bn, ++*runp);
  253                         bn = ap->in_off;
  254                         if (runb && bn) {
  255                                 for (--bn; bn >= 0 && *runb < maxrun &&
  256                                         is_sequential(ump,
  257                                         ((e2fs_daddr_t *)bp->b_data)[bn],
  258                                         ((e2fs_daddr_t *)bp->b_data)[bn + 1]);
  259                                         --bn, ++*runb);
  260                         }
  261                 }
  262         }
  263         if (bp)
  264                 bqrelse(bp);
  265 
  266         /*
  267          * Since this is FFS independent code, we are out of scope for the
  268          * definitions of BLK_NOCOPY and BLK_SNAP, but we do know that they
  269          * will fall in the range 1..um_seqinc, so we use that test and
  270          * return a request for a zeroed out buffer if attempts are made
  271          * to read a BLK_NOCOPY or BLK_SNAP block.
  272          */
  273         if ((ip->i_flags & SF_SNAPSHOT) && daddr > 0 && daddr < ump->um_seqinc) {
  274                 *bnp = -1;
  275                 return (0);
  276         }
  277         *bnp = blkptrtodb(ump, daddr);
  278         if (*bnp == 0) {
  279                 *bnp = -1;
  280         }
  281         return (0);
  282 }
  283 
  284 /*
  285  * Create an array of logical block number/offset pairs which represent the
  286  * path of indirect blocks required to access a data block.  The first "pair"
  287  * contains the logical block number of the appropriate single, double or
  288  * triple indirect block and the offset into the inode indirect block array.
  289  * Note, the logical block number of the inode single/double/triple indirect
  290  * block appears twice in the array, once with the offset into the i_ib and
  291  * once with the offset into the page itself.
  292  */
  293 int
  294 ext2_getlbns(struct vnode *vp, daddr_t bn, struct indir *ap, int *nump)
  295 {
  296         long blockcnt;
  297         e2fs_lbn_t metalbn, realbn;
  298         struct ext2mount *ump;
  299         int i, numlevels, off;
  300         int64_t qblockcnt;
  301 
  302         ump = VFSTOEXT2(vp->v_mount);
  303         if (nump)
  304                 *nump = 0;
  305         numlevels = 0;
  306         realbn = bn;
  307         if ((long)bn < 0)
  308                 bn = -(long)bn;
  309 
  310         /* The first NDADDR blocks are direct blocks. */
  311         if (bn < NDADDR)
  312                 return (0);
  313 
  314         /*
  315          * Determine the number of levels of indirection.  After this loop
  316          * is done, blockcnt indicates the number of data blocks possible
  317          * at the previous level of indirection, and NIADDR - i is the number
  318          * of levels of indirection needed to locate the requested block.
  319          */
  320         for (blockcnt = 1, i = NIADDR, bn -= NDADDR;; i--, bn -= blockcnt) {
  321                 if (i == 0)
  322                         return (EFBIG);
  323                 /*
  324                  * Use int64_t's here to avoid overflow for triple indirect
  325                  * blocks when longs have 32 bits and the block size is more
  326                  * than 4K.
  327                  */
  328                 qblockcnt = (int64_t)blockcnt * MNINDIR(ump);
  329                 if (bn < qblockcnt)
  330                         break;
  331                 blockcnt = qblockcnt;
  332         }
  333 
  334         /* Calculate the address of the first meta-block. */
  335         if (realbn >= 0)
  336                 metalbn = -(realbn - bn + NIADDR - i);
  337         else
  338                 metalbn = -(-realbn - bn + NIADDR - i);
  339 
  340         /*
  341          * At each iteration, off is the offset into the bap array which is
  342          * an array of disk addresses at the current level of indirection.
  343          * The logical block number and the offset in that block are stored
  344          * into the argument array.
  345          */
  346         ap->in_lbn = metalbn;
  347         ap->in_off = off = NIADDR - i;
  348         ap++;
  349         for (++numlevels; i <= NIADDR; i++) {
  350                 /* If searching for a meta-data block, quit when found. */
  351                 if (metalbn == realbn)
  352                         break;
  353 
  354                 off = (bn / blockcnt) % MNINDIR(ump);
  355 
  356                 ++numlevels;
  357                 ap->in_lbn = metalbn;
  358                 ap->in_off = off;
  359                 ++ap;
  360 
  361                 metalbn -= -1 + off * blockcnt;
  362                 blockcnt /= MNINDIR(ump);
  363         }
  364         if (nump)
  365                 *nump = numlevels;
  366         return (0);
  367 }

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