1 files changed, 67 insertions, 0 deletions
diff --git a/sys/fs/msdosfs/msdosfs_fat.c b/sys/fs/msdosfs/msdosfs_fat.c
index 1e9a3cf..1f75d7a 100644
--- a/sys/fs/msdosfs/msdosfs_fat.c
+++ b/sys/fs/msdosfs/msdosfs_fat.c
@@ -1106,3 +1106,70 @@ extendfile(dep, count, bpp, ncp, flags)
 
 	return (0);
 }
+
+/* [2753891]
+ * Routine to mark a FAT16 or FAT32 volume as "clean" or "dirty" by manipulating the upper bit
+ * of the FAT entry for cluster 1.  Note that this bit is not defined for FAT12 volumes, which
+ * are always assumed to be dirty.
+ *
+ * The fatentry() routine only works on cluster numbers that a file could occupy, so it won't
+ * manipulate the entry for cluster 1.  So we have to do it here.  The code is ripped from
+ * fatentry(), and tailored for cluster 1.
+ *
+ * Inputs:
+ *     pmp     The MS-DOS volume to mark
+ *     dirty   Non-zero if the volume should be marked dirty; zero if it should be marked clean.
+ *
+ * Result:
+ *     0       Success
+ *     EROFS   Volume is read-only
+ *     ?       (other errors from called routines)
+ */
+int markvoldirty(struct msdosfsmount *pmp, int dirty)
+{
+    int error;
+    u_long bn, bo, bsize, byteoffset;
+    u_long fatval;
+    struct buf *bp;
+
+    /* FAT12 does not support a "clean" bit, so don't do anything */
+    if (FAT12(pmp))
+        return 0;
+
+    /* Can't change the bit on a read-only filesystem */
+    if (pmp->pm_flags & MSDOSFSMNT_RONLY)
+        return EROFS;
+
+    /* Fetch the block containing the FAT entry */
+    byteoffset = FATOFS(pmp, 1);       /* Find the location of cluster 1 */
+    fatblock(pmp, byteoffset, &bn, &bsize, &bo);
+    
+    error = bread(pmp->pm_devvp, bn, bsize, NOCRED, &bp);
+    if (error) {
+            brelse(bp);
+            return (error);
+    }
+
+    /* Get the current value of the FAT entry and set/clear the high bit */
+    if (FAT32(pmp)) {
+        /* FAT32 uses bit 27 */
+        fatval = getulong(&bp->b_data[bo]);
+        if (dirty)
+            fatval &= 0xF7FFFFFF;      /* dirty means clear the "clean" bit */
+        else
+            fatval |= 0x08000000;      /* clean means set the "clean" bit */
+        putulong(&bp->b_data[bo], fatval);
+    }
+    else {
+        /* Must be FAT16; use bit 15 */
+        fatval = getushort(&bp->b_data[bo]);
+        if (dirty)
+            fatval &= 0x7FFF;          /* dirty means clear the "clean" bit */
+        else
+            fatval |= 0x8000;          /* clean means set the "clean" bit */
+        putushort(&bp->b_data[bo], fatval);
+    }
+
+    /* Write out the modified FAT block immediately */
+    return bwrite(bp);
+}