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Date:      Fri, 24 Dec 1999 01:50:02 -0800 (PST)
From:      Boris Popov <bp@butya.kz>
To:        freebsd-bugs@FreeBSD.org
Subject:   Re: kern/15136: Panic on MSDOS FS mount
Message-ID:  <199912240950.BAA88522@freefall.freebsd.org>
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The following reply was made to PR kern/15136; it has been noted by GNATS.

From: Boris Popov <bp@butya.kz>
To: freebsd-gnats-submit@freebsd.org, netch@lucky.net
Cc:  
Subject: Re: kern/15136: Panic on MSDOS FS mount
Date: Fri, 24 Dec 1999 15:41:23 +0600

 > On attempt to mount MSDOS (FAT16) file system, kernel falls to panic with
 >      message:
 >      panic: vm_fault: fault on nofault entry, addr=c16de000
 
 	This caused by inconsistent data in the boot record. Could please test
 the following patch and tell me if this helps:
 
 diff -u ../msdosfs_vfsops.c ./msdosfs_vfsops.c
 --- ../msdosfs_vfsops.c Sun Dec 19 12:07:56 1999
 +++ ./msdosfs_vfsops.c  Fri Dec 24 15:15:08 1999
 @@ -364,6 +364,7 @@
         struct byte_bpb50 *b50;
         struct byte_bpb710 *b710;
         u_int8_t SecPerClust;
 +       u_long clusters;
         int     ronly, error;
  
         /*
 @@ -595,14 +596,13 @@
                 pmp->pm_firstcluster = pmp->pm_rootdirblk +
 pmp->pm_rootdirsize;
         }
  
 -       pmp->pm_nmbrofclusters = (pmp->pm_HugeSectors - pmp->pm_firstcluster)
 /
 -           SecPerClust;
 -       pmp->pm_maxcluster = pmp->pm_nmbrofclusters + 1;
 +       pmp->pm_maxcluster = (pmp->pm_HugeSectors - pmp->pm_firstcluster) /
 +           SecPerClust + 1;
         pmp->pm_fatsize = pmp->pm_FATsecs * pmp->pm_BytesPerSec;
  
  #ifndef __FreeBSD__
         if (argp->flags & MSDOSFSMNT_GEMDOSFS) {
 -               if ((pmp->pm_nmbrofclusters <= (0xff0 - 2))
 +               if ((pmp->pm_maxcluster <= (0xff0 - 2))
                       && ((dtype == DTYPE_FLOPPY) || ((dtype == DTYPE_VNODE)
                       && ((pmp->pm_Heads == 1) || (pmp->pm_Heads == 2))))
                     ) {
 @@ -633,6 +633,15 @@
                         pmp->pm_fatdiv = 1;
                 }
         }
 +
 +       clusters = (pmp->pm_fatsize / pmp->pm_fatmult) * pmp->pm_fatdiv;
 +       if (pmp->pm_maxcluster >= clusters) {
 +               printf("Warning: number of clusters (%ld) exceeds FAT "
 +                   "capasity (%ld)\n", pmp->pm_maxcluster + 1, clusters);
 +               pmp->pm_maxcluster = clusters - 1;
 +       }
 +
 +
         if (FAT12(pmp))
                 pmp->pm_fatblocksize = 3 * pmp->pm_BytesPerSec;
         else
 @@ -829,7 +838,7 @@
         pmp = VFSTOMSDOSFS(mp);
         sbp->f_bsize = pmp->pm_bpcluster;
         sbp->f_iosize = pmp->pm_bpcluster;
 -       sbp->f_blocks = pmp->pm_nmbrofclusters;
 +       sbp->f_blocks = pmp->pm_maxcluster + 1;
         sbp->f_bfree = pmp->pm_freeclustercount;
         sbp->f_bavail = pmp->pm_freeclustercount;
         sbp->f_files = pmp->pm_RootDirEnts;                     /* XXX */
 diff -u ../msdosfsmount.h ./msdosfsmount.h
 --- ../msdosfsmount.h   Sat Aug 28 07:48:11 1999
 +++ ./msdosfsmount.h    Fri Dec 24 12:18:12 1999
 @@ -73,7 +73,6 @@
         u_long pm_rootdirblk;   /* block # (cluster # for FAT32) of root
 directory number */
         u_long pm_rootdirsize;  /* size in blocks (not clusters) */
         u_long pm_firstcluster; /* block number of first cluster */
 -       u_long pm_nmbrofclusters;       /* # of clusters in filesystem */
         u_long pm_maxcluster;   /* maximum cluster number */
         u_long pm_freeclustercount;     /* number of free clusters */
         u_long pm_cnshift;      /* shift file offset right this amount to get
 a cluster number */
 


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