infra: account for truncated files

kernel/lib_mapfree.c

@@ -146,9 +146,22 @@ struct mapfree_info *mapfree_get(const char *name, int flags)
 		}
 		up_read(&mapfree_mutex);
 	
-		if (mf)
+		if (mf) {
+			struct inode *inode = mf->mf_filp->f_mapping->host;
+			loff_t length;
+			int i;
+
+			/* In some cases like truncated logfiles,
+			 * account for any shortenings.
+			 */
+			length = i_size_read(inode);
+			mf->mf_max = length;
+			for (i = 0; i < DIRTY_MAX; i++)
+				mf_dirty_reduce(mf, i, length);
+
 			goto done;
 		}
+	}
 
 	for (;;) {
 		struct address_space *mapping;
@@ -338,6 +351,17 @@ void mf_dirty_append(struct mapfree_info *mf, enum dirty_stage stage, loff_t new
 	traced_writeunlock(&dl->dl_lock, flags);
 }
 
+void mf_dirty_reduce(struct mapfree_info *mf, enum dirty_stage stage, loff_t newlen)
+{
+	struct dirty_length *dl = _get_dl(mf, stage);
+	unsigned long flags;
+
+	traced_writelock(&dl->dl_lock, flags);
+	if (dl->dl_length > newlen)
+		dl->dl_length = newlen;
+	traced_writeunlock(&dl->dl_lock, flags);
+}
+
 loff_t mf_dirty_length(struct mapfree_info *mf, enum dirty_stage stage)
 {
 	struct dirty_length *dl = _get_dl(mf, stage);

kernel/lib_mapfree.h

@@ -87,6 +87,7 @@ void mapfree_pages(struct mapfree_info *mf, int grace_keep);
 ////////////////// dirty IOs in append mode  //////////////////
 
 void mf_dirty_append(struct mapfree_info *mf, enum dirty_stage stage, loff_t newlen);
+void mf_dirty_reduce(struct mapfree_info *mf, enum dirty_stage stage, loff_t newlen);
 loff_t mf_dirty_length(struct mapfree_info *mf, enum dirty_stage stage);
 
 ////////////////// dirty IOs on the fly  //////////////////