FreeBSD/Linux Kernel Cross Reference
sys/fs/msdosfs/msdosfs_fileno.c

     /*-
      * Copyright (c) 2003-2004 Tim J. Robbins.
      * All rights reserved.
      *
      * 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.
     *
     * THIS SOFTWARE IS PROVIDED BY THE AUTHOR 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 AUTHOR 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.
     */
    /*
     * Compress 64-bit file numbers into temporary, unique 32-bit file numbers.
     * This is needed because the algorithm we use to calculate these numbers
     * generates 64-bit quantities, but struct dirent's d_fileno member and
     * struct vnodeattr's va_fileid member only have space for 32 bits.
     *
     * 32-bit file numbers are generated sequentially, and stored in a
     * red-black tree, indexed on 64-bit file number. The mappings do not
     * persist across reboots (or unmounts); anything that relies on this
     * (e.g. NFS) will not work correctly. This scheme consumes 32 bytes
     * of kernel memory per file (on i386), and it may be possible for a user
     * to cause a panic by creating millions of tiny files.
     *
     * As an optimization, we split the file number space between statically
     * allocated and dynamically allocated. File numbers less than
     * FILENO_FIRST_DYN are left unchanged and do not have any tree nodes
     * allocated to them.
     */
    
    #include <sys/cdefs.h>
    __FBSDID("$FreeBSD: releng/11.0/sys/fs/msdosfs/msdosfs_fileno.c 276887 2015-01-09 14:50:08Z emaste $");
    
    #include <sys/param.h>
    #include <sys/systm.h>
    #include <sys/kernel.h>
    #include <sys/lock.h>
    #include <sys/malloc.h>
    #include <sys/mount.h>
    
    #include <fs/msdosfs/bpb.h>
    #include <fs/msdosfs/direntry.h>
    #include <fs/msdosfs/msdosfsmount.h>
    
    static MALLOC_DEFINE(M_MSDOSFSFILENO, "msdosfs_fileno", "MSDOSFS fileno mapping node");
    
    RB_PROTOTYPE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
        msdosfs_fileno_compare)
    
    static int msdosfs_fileno_compare(struct msdosfs_fileno *,
        struct msdosfs_fileno *);
    
    #define FILENO_FIRST_DYN        0xf0000000
    
    /* Initialize file number mapping structures. */
    void
    msdosfs_fileno_init(struct mount *mp)
    {
            struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
    
            RB_INIT(&pmp->pm_filenos);
            pmp->pm_nfileno = FILENO_FIRST_DYN;
            if (pmp->pm_HugeSectors > 0xffffffff /
                (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1)
                    pmp->pm_flags |= MSDOSFS_LARGEFS;
    }
    
    /* Free 32-bit file number generation structures. */
    void
    msdosfs_fileno_free(struct mount *mp)
    {
            struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
            struct msdosfs_fileno *mf, *next;
    
            for (mf = RB_MIN(msdosfs_filenotree, &pmp->pm_filenos); mf != NULL;
                mf = next) {
                    next = RB_NEXT(msdosfs_filenotree, &pmp->pm_filenos, mf);
                    RB_REMOVE(msdosfs_filenotree, &pmp->pm_filenos, mf);
                    free(mf, M_MSDOSFSFILENO);
            }
    }
    
    /* Map a 64-bit file number into a 32-bit one. */
    uint32_t
    msdosfs_fileno_map(struct mount *mp, uint64_t fileno)
   {
           struct msdosfsmount *pmp = VFSTOMSDOSFS(mp);
           struct msdosfs_fileno key, *mf, *tmf;
           uint32_t mapped;
   
           if ((pmp->pm_flags & MSDOSFS_LARGEFS) == 0) {
                   KASSERT((uint32_t)fileno == fileno,
                       ("fileno >32 bits but not a large fs?"));
                   return ((uint32_t)fileno);
           }
           if (fileno < FILENO_FIRST_DYN)
                   return ((uint32_t)fileno);
           MSDOSFS_LOCK_MP(pmp);
           key.mf_fileno64 = fileno;
           mf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
           if (mf != NULL) {
                   mapped = mf->mf_fileno32;
                   MSDOSFS_UNLOCK_MP(pmp);
                   return (mapped);
           }
           if (pmp->pm_nfileno < FILENO_FIRST_DYN)
                   panic("msdosfs_fileno_map: wraparound");
           MSDOSFS_UNLOCK_MP(pmp);
           mf = malloc(sizeof(*mf), M_MSDOSFSFILENO, M_WAITOK);
           MSDOSFS_LOCK_MP(pmp);
           tmf = RB_FIND(msdosfs_filenotree, &pmp->pm_filenos, &key);
           if (tmf != NULL) {
                   mapped = tmf->mf_fileno32;
                   MSDOSFS_UNLOCK_MP(pmp);
                   free(mf, M_MSDOSFSFILENO);
                   return (mapped);
           }
           mf->mf_fileno64 = fileno;
           mapped = mf->mf_fileno32 = pmp->pm_nfileno++;
           RB_INSERT(msdosfs_filenotree, &pmp->pm_filenos, mf);
           MSDOSFS_UNLOCK_MP(pmp);
           return (mapped);
   }
   
   /* Compare by 64-bit file number. */
   static int
   msdosfs_fileno_compare(struct msdosfs_fileno *fa, struct msdosfs_fileno *fb)
   {
   
           if (fa->mf_fileno64 > fb->mf_fileno64)
                   return (1);
           else if (fa->mf_fileno64 < fb->mf_fileno64)
                   return (-1);
           return (0);
   }
   
   RB_GENERATE(msdosfs_filenotree, msdosfs_fileno, mf_tree,
       msdosfs_fileno_compare)

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