[PATCH] ufs: truncate correction

1) When we allocated last fragment in ufs_truncate, we read page, check
if block mapped to address, and if not trying to allocate it. This is
wrong behaviour, fragment may be NOT allocated, but mapped, this
happened because of "block map" function not checked allocated fragment
or not, it just take address of the first fragment in the block, add
offset of fragment and return result, this is correct behaviour in
almost all situation except call from ufs_truncate.

2) Almost all implementation of UFS, which I can investigate have such
"defect": if you have full disk, and try truncate file, for example 3GB
to 2MB, and have hole in this region, truncate return -ENOSPC. I tried
evade from this problem, but "block allocation" algorithm is tied to
right value of i_lastfrag, and fix of this corner case may slow down of
ordinaries scenarios, so this patch makes behavior of "truncate"
operations similar to what other UFS implementations do.

Signed-off-by: Evgeniy Dushistov <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

fs/ufs/truncate.c

···
 	int err = 0;
 	struct address_space *mapping = inode->i_mapping;
 	struct ufs_sb_private_info *uspi = UFS_SB(inode->i_sb)->s_uspi;
-	struct ufs_inode_info *ufsi = UFS_I(inode);
 	unsigned lastfrag, i, end;
 	struct page *lastpage;
 	struct buffer_head *bh;
 
 	lastfrag = (i_size_read(inode) + uspi->s_fsize - 1) >> uspi->s_fshift;
 
-	if (!lastfrag) {
-		ufsi->i_lastfrag = 0;
+	if (!lastfrag)
 		goto out;
-	}
+
 	lastfrag--;
 
 	lastpage = ufs_get_locked_page(mapping, lastfrag >>
···
        for (i = 0; i < end; ++i)
                bh = bh->b_this_page;
 
-       if (!buffer_mapped(bh)) {
-               err = ufs_getfrag_block(inode, lastfrag, bh, 1);
 
-               if (unlikely(err))
-                       goto out_unlock;
+       err = ufs_getfrag_block(inode, lastfrag, bh, 1);
 
-               if (buffer_new(bh)) {
-                       clear_buffer_new(bh);
-                       unmap_underlying_metadata(bh->b_bdev,
-						 bh->b_blocknr);
-		       /*
-			* we do not zeroize fragment, because of
-			* if it maped to hole, it already contains zeroes
-			*/
-                       set_buffer_uptodate(bh);
-                       mark_buffer_dirty(bh);
-                       set_page_dirty(lastpage);
-               }
+       if (unlikely(err))
+	       goto out_unlock;
+
+       if (buffer_new(bh)) {
+	       clear_buffer_new(bh);
+	       unmap_underlying_metadata(bh->b_bdev,
+					 bh->b_blocknr);
+	       /*
+		* we do not zeroize fragment, because of
+		* if it maped to hole, it already contains zeroes
+		*/
+	       set_buffer_uptodate(bh);
+	       mark_buffer_dirty(bh);
+	       set_page_dirty(lastpage);
        }
+
 out_unlock:
        ufs_put_locked_page(lastpage);
 out:
···
 	if (IS_APPEND(inode) || IS_IMMUTABLE(inode))
 		return -EPERM;
 
-	if (inode->i_size > old_i_size) {
-		/*
-		 * if we expand file we should care about
-		 * allocation of block for last byte first of all
-		 */
-		err = ufs_alloc_lastblock(inode);
+	err = ufs_alloc_lastblock(inode);
 
-		if (err) {
-			i_size_write(inode, old_i_size);
-			goto out;
-		}
-		/*
-		 * go away, because of we expand file, and we do not
-		 * need free blocks, and zeroizes page
-		 */
-		lock_kernel();
-		goto almost_end;
+	if (err) {
+		i_size_write(inode, old_i_size);
+		goto out;
 	}
 
 	block_truncate_page(inode->i_mapping, inode->i_size, ufs_getfrag_block);
···
 		yield();
 	}
 
-	if (inode->i_size < old_i_size) {
-		/*
-		 * now we should have enough space
-		 * to allocate block for last byte
-		 */
-		err = ufs_alloc_lastblock(inode);
-		if (err)
-			/*
-			 * looks like all the same - we have no space,
-			 * but we truncate file already
-			 */
-			inode->i_size = (ufsi->i_lastfrag - 1) * uspi->s_fsize;
-	}
-almost_end:
 	inode->i_mtime = inode->i_ctime = CURRENT_TIME_SEC;
+	ufsi->i_lastfrag = DIRECT_FRAGMENT;
 	unlock_kernel();
 	mark_inode_dirty(inode);
 out: