clean up vmtruncate

vmtruncate is a twisted maze of gotos, this patch cleans it up to have a
proper if else for the two major cases of extending and truncating truncate
and thus makes it a lot more readable while keeping exactly the same
functinality.
Signed-off-by: NChristoph Hellwig <hch@lst.de>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memory.c

@@ -1909,50 +1909,49 @@ EXPORT_SYMBOL(unmap_mapping_range);
  */
 int vmtruncate(struct inode * inode, loff_t offset)
 {
-	struct address_space *mapping = inode->i_mapping;
-	unsigned long limit;
+	if (inode->i_size < offset) {
+		unsigned long limit;
+
+		limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
+		if (limit != RLIM_INFINITY && offset > limit)
+			goto out_sig;
+		if (offset > inode->i_sb->s_maxbytes)
+			goto out_big;
+		i_size_write(inode, offset);
+	} else {
+		struct address_space *mapping = inode->i_mapping;
 
-	if (inode->i_size < offset)
-		goto do_expand;
-	/*
-	 * truncation of in-use swapfiles is disallowed - it would cause
-	 * subsequent swapout to scribble on the now-freed blocks.
-	 */
-	if (IS_SWAPFILE(inode))
-		goto out_busy;
-	i_size_write(inode, offset);
+		/*
+		 * truncation of in-use swapfiles is disallowed - it would
+		 * cause subsequent swapout to scribble on the now-freed
+		 * blocks.
+		 */
+		if (IS_SWAPFILE(inode))
+			return -ETXTBSY;
+		i_size_write(inode, offset);
+
+		/*
+		 * unmap_mapping_range is called twice, first simply for
+		 * efficiency so that truncate_inode_pages does fewer
+		 * single-page unmaps.  However after this first call, and
+		 * before truncate_inode_pages finishes, it is possible for
+		 * private pages to be COWed, which remain after
+		 * truncate_inode_pages finishes, hence the second
+		 * unmap_mapping_range call must be made for correctness.
+		 */
+		unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
+		truncate_inode_pages(mapping, offset);
+		unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
+	}
 
-	/*
-	 * unmap_mapping_range is called twice, first simply for efficiency
-	 * so that truncate_inode_pages does fewer single-page unmaps. However
-	 * after this first call, and before truncate_inode_pages finishes,
-	 * it is possible for private pages to be COWed, which remain after
-	 * truncate_inode_pages finishes, hence the second unmap_mapping_range
-	 * call must be made for correctness.
-	 */
-	unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
-	truncate_inode_pages(mapping, offset);
-	unmap_mapping_range(mapping, offset + PAGE_SIZE - 1, 0, 1);
-	goto out_truncate;
-
-do_expand:
-	limit = current->signal->rlim[RLIMIT_FSIZE].rlim_cur;
-	if (limit != RLIM_INFINITY && offset > limit)
-		goto out_sig;
-	if (offset > inode->i_sb->s_maxbytes)
-		goto out_big;
-	i_size_write(inode, offset);
-
-out_truncate:
 	if (inode->i_op && inode->i_op->truncate)
 		inode->i_op->truncate(inode);
 	return 0;
+
 out_sig:
 	send_sig(SIGXFSZ, current, 0);
 out_big:
 	return -EFBIG;
-out_busy:
-	return -ETXTBSY;
 }
 EXPORT_SYMBOL(vmtruncate);