Add a "-o large" mount option for msdosfs. Convert compile-time checks for

#ifdef MSDOSFS_LARGE to run-time checks to see if "-o large" was specified.

Test case provided by Oliver Fromme:
  truncate -s 200G test.img
  mdconfig -a -t vnode -f test.img -u 9
  newfs_msdos -s 419430400 -n 1 /dev/md9 zip250
  mount -t msdosfs /dev/md9 /mnt    # should fail
  mount -t msdosfs -o large /dev/md9 /mnt   # should succeed

PR:		105964
Requested by:	Oliver Fromme <olli lurza secnetix de>
Tested by:	trhodes
MFC after:	2 weeks

2 files changed, 54 insertions, 36 deletions

diff --git a/sys/fs/msdosfs/msdosfs_vfsops.c b/sys/fs/msdosfs/msdosfs_vfsops.c
index 5bc7ba8..d1999e9 100644
--- a/sys/fs/msdosfs/msdosfs_vfsops.c
+++ b/sys/fs/msdosfs/msdosfs_vfsops.c
@@ -83,7 +83,7 @@ static const char *msdosfs_opts[] = {
 	"export", "force", "sync",
 	"uid", "gid", "mask", "dirmask",
 	"shortname", "shortnames", "longname", "longnames", "nowin95", "win95",
-	"kiconv", "cs_win", "cs_dos", "cs_local",
+	"kiconv", "cs_win", "cs_dos", "cs_local", "large",
 	NULL
 };
 
@@ -467,6 +467,21 @@ mountmsdosfs(devvp, mp, td)
 	pmp->pm_bo = bo;
 
 	/*
+	 * Experimental support for large MS-DOS filesystems.
+	 * WARNING: This uses at least 32 bytes of kernel memory (which is not
+	 * reclaimed until the FS is unmounted) for each file on disk to map
+	 * between the 32-bit inode numbers used by VFS and the 64-bit
+	 * pseudo-inode numbers used internally by msdosfs. This is only
+	 * safe to use in certain controlled situations (e.g. read-only FS
+	 * with less than 1 million files).
+	 * Since the mappings do not persist across unmounts (or reboots), these
+	 * filesystems are not suitable for exporting through NFS, or any other
+	 * application that requires fixed inode numbers.
+	 */
+	vfs_flagopt(mp->mnt_optnew, "large", &pmp->pm_flags,
+	  MSDOSFS_LARGEFS);
+
+	/*
 	 * Compute several useful quantities from the bpb in the
 	 * bootsector.  Copy in the dos 5 variant of the bpb then fix up
 	 * the fields that are different between dos 5 and dos 3.3.
@@ -508,19 +523,20 @@ mountmsdosfs(devvp, mp, td)
 		pmp->pm_HiddenSects = getushort(b33->bpbHiddenSecs);
 		pmp->pm_HugeSectors = pmp->pm_Sectors;
 	}
-#ifndef MSDOSFS_LARGE
-	if (pmp->pm_HugeSectors > 0xffffffff / 
-	    (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1) {
-		/*
-		 * We cannot deal currently with this size of disk
-		 * due to fileid limitations (see msdosfs_getattr and
-		 * msdosfs_readdir)
-		 */
-		error = EINVAL;
-		printf("mountmsdosfs(): disk too big, sorry\n");
-		goto error_exit;
+	if (!(pmp->pm_flags & MSDOSFS_LARGEFS)) {
+		if (pmp->pm_HugeSectors > 0xffffffff / 
+		    (pmp->pm_BytesPerSec / sizeof(struct direntry)) + 1) {
+			/*
+			 * We cannot deal currently with this size of disk
+			 * due to fileid limitations (see msdosfs_getattr and
+			 * msdosfs_readdir)
+			 */
+			error = EINVAL;
+			vfs_mount_error(mp,
+			    "Disk too big, try '-o large' mount option");
+			goto error_exit;
+		}
 	}
-#endif	/* !MSDOSFS_LARGE */
 
 	if (pmp->pm_RootDirEnts == 0) {
 		if (pmp->pm_Sectors
@@ -721,9 +737,8 @@ mountmsdosfs(devvp, mp, td)
 	mp->mnt_flag |= MNT_LOCAL;
 	MNT_IUNLOCK(mp);
 
-#ifdef MSDOSFS_LARGE
-	msdosfs_fileno_init(mp);
-#endif
+	if (pmp->pm_flags & MSDOSFS_LARGEFS)
+		msdosfs_fileno_init(mp);
 
 	return 0;
 
@@ -806,9 +821,9 @@ msdosfs_unmount(mp, mntflags, td)
 	PICKUP_GIANT();
 	vrele(pmp->pm_devvp);
 	free(pmp->pm_inusemap, M_MSDOSFSFAT);
-#ifdef MSDOSFS_LARGE
-	msdosfs_fileno_free(mp);
-#endif
+	if (pmp->pm_flags & MSDOSFS_LARGEFS) {
+		msdosfs_fileno_free(mp);
+	}
 	free(pmp, M_MSDOSFSMNT);
 	mp->mnt_data = (qaddr_t)0;
 	MNT_ILOCK(mp);
diff --git a/sys/fs/msdosfs/msdosfs_vnops.c b/sys/fs/msdosfs/msdosfs_vnops.c
index 57b0ec8..cc0a046 100644
--- a/sys/fs/msdosfs/msdosfs_vnops.c
+++ b/sys/fs/msdosfs/msdosfs_vnops.c
@@ -326,11 +326,12 @@ msdosfs_getattr(ap)
 			fileid = (uint64_t)roottobn(pmp, 0) * dirsperblk;
 		fileid += (uint64_t)dep->de_diroffset / sizeof(struct direntry);
 	}
-#ifdef MSDOSFS_LARGE
-	vap->va_fileid = msdosfs_fileno_map(pmp->pm_mountp, fileid);
-#else
-	vap->va_fileid = (long)fileid;
-#endif
+
+	if (pmp->pm_flags & MSDOSFS_LARGEFS)
+		vap->va_fileid = msdosfs_fileno_map(pmp->pm_mountp, fileid);
+	else
+		vap->va_fileid = (long)fileid;
+
 	if ((dep->de_Attributes & ATTR_READONLY) == 0)
 		mode = S_IRWXU|S_IRWXG|S_IRWXO;
 	else
@@ -1571,12 +1572,14 @@ msdosfs_readdir(ap)
 							  * dirsperblk;
 				else
 					fileno = 1;
-#ifdef MSDOSFS_LARGE
-				dirbuf.d_fileno = msdosfs_fileno_map(
-				    pmp->pm_mountp, fileno);
-#else
-				dirbuf.d_fileno = (uint32_t)fileno;
-#endif
+				if (pmp->pm_flags & MSDOSFS_LARGEFS) {
+					dirbuf.d_fileno =
+					    msdosfs_fileno_map(pmp->pm_mountp,
+					    fileno);
+				} else {
+
+					dirbuf.d_fileno = (uint32_t)fileno;
+				}
 				dirbuf.d_type = DT_DIR;
 				switch (n) {
 				case 0:
@@ -1700,12 +1703,12 @@ msdosfs_readdir(ap)
 				fileno = (uint64_t)offset / sizeof(struct direntry);
 				dirbuf.d_type = DT_REG;
 			}
-#ifdef MSDOSFS_LARGE
-			dirbuf.d_fileno = msdosfs_fileno_map(pmp->pm_mountp,
-			    fileno);
-#else
-			dirbuf.d_fileno = (uint32_t)fileno;
-#endif
+			if (pmp->pm_flags & MSDOSFS_LARGEFS) {
+				dirbuf.d_fileno =
+				    msdosfs_fileno_map(pmp->pm_mountp, fileno);
+			} else
+				dirbuf.d_fileno = (uint32_t)fileno;
+
 			if (chksum != winChksum(dentp)) {
 				dirbuf.d_namlen = dos2unixfn(dentp->deName,
 				    (u_char *)dirbuf.d_name,