[GFS2] Update truncate function (shrinking partial blocks)

Update the function in GFS2 which deals with truncation of
partial blocks. Some of the code is "borrowed" from ext3
since it appears to give a good model of how to do this
operation. The function is renamed gfs2_block_truncate_page
accordingly.
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

fs/gfs2/bmap.c

@@ -872,7 +872,7 @@ static int trunc_start(struct gfs2_inode *ip, uint64_t size)
 			if (do_div(junk, sdp->sd_jbsize))
 				error = truncator_journaled(ip, size);
 		} else if (size & (uint64_t)(sdp->sd_sb.sb_bsize - 1))
-			error = gfs2_truncator_page(ip, size);
+			error = gfs2_block_truncate_page(ip->i_vnode->i_mapping);
 
 		if (!error) {
 			ip->i_di.di_size = size;

fs/gfs2/ops_address.c

@@ -385,7 +385,7 @@ static int gfs2_commit_write(struct file *file, struct page *page,
 			i_size_write(inode, file_size);
 	} else {
 		if (sdp->sd_args.ar_data == GFS2_DATA_ORDERED)
-			gfs2_page_add_databufs(sdp, page, from, to);
+			gfs2_page_add_databufs(ip, page, from, to);
 		error = generic_commit_write(file, page, from, to);
 		if (error)
 			goto fail;

fs/gfs2/page.c

@@ -21,6 +21,7 @@
 #include "inode.h"
 #include "page.h"
 #include "trans.h"
+#include "ops_address.h"
 
 /**
  * gfs2_pte_inval - Sync and invalidate all PTEs associated with a glock
@@ -184,76 +185,81 @@ int gfs2_unstuffer_page(struct gfs2_inode *ip, struct buffer_head *dibh,
 }
 
 /**
- * gfs2_truncator_page - truncate a partial data block in the page cache
- * @ip: the inode
- * @size: the size the file should be
+ * gfs2_block_truncate_page - Deal with zeroing out data for truncate
  *
- * Returns: errno
+ * This is partly borrowed from ext3.
  */
-
-int gfs2_truncator_page(struct gfs2_inode *ip, uint64_t size)
+int gfs2_block_truncate_page(struct address_space *mapping)
 {
+	struct inode *inode = mapping->host;
+	struct gfs2_inode *ip = get_v2ip(inode);
 	struct gfs2_sbd *sdp = ip->i_sbd;
-	struct inode *inode = ip->i_vnode;
-	struct page *page;
+	loff_t from = inode->i_size;
+	unsigned long index = from >> PAGE_CACHE_SHIFT;
+	unsigned offset = from & (PAGE_CACHE_SIZE-1);
+	unsigned blocksize, iblock, length, pos;
 	struct buffer_head *bh;
+	struct page *page;
 	void *kaddr;
-	uint64_t lbn, dbn;
-	unsigned long index;
-	unsigned int offset;
-	unsigned int bufnum;
-	int new = 0;
-	int error;
-
-	lbn = size >> inode->i_blkbits;
-	error = gfs2_block_map(ip, lbn, &new, &dbn, NULL);
-	if (error || !dbn)
-		return error;
-
-	index = size >> PAGE_CACHE_SHIFT;
-	offset = size & (PAGE_CACHE_SIZE - 1);
-	bufnum = lbn - (index << (PAGE_CACHE_SHIFT - inode->i_blkbits));
-
-	page = read_cache_page(inode->i_mapping, index,
-			       (filler_t *)inode->i_mapping->a_ops->readpage,
-			       NULL);
-	if (IS_ERR(page))
-		return PTR_ERR(page);
-
-	lock_page(page);
-
-	if (!PageUptodate(page) || PageError(page)) {
-		error = -EIO;
-		goto out;
-	}
+	int err;
+
+	page = grab_cache_page(mapping, index);
+	if (!page)
+		return 0;
 
-	kaddr = kmap(page);
-	memset(kaddr + offset, 0, PAGE_CACHE_SIZE - offset);
-	kunmap(page);
+	blocksize = inode->i_sb->s_blocksize;
+	length = blocksize - (offset & (blocksize - 1));
+	iblock = index << (PAGE_CACHE_SHIFT - inode->i_sb->s_blocksize_bits);
 
 	if (!page_has_buffers(page))
-		create_empty_buffers(page, 1 << inode->i_blkbits,
-				     (1 << BH_Uptodate));
+		create_empty_buffers(page, blocksize, 0);
 
-	for (bh = page_buffers(page); bufnum--; bh = bh->b_this_page)
-		/* Do nothing */;
+	/* Find the buffer that contains "offset" */
+	bh = page_buffers(page);
+	pos = blocksize;
+	while (offset >= pos) {
+		bh = bh->b_this_page;
+		iblock++;
+		pos += blocksize;
+	}
 
-	if (!buffer_mapped(bh))
-		map_bh(bh, inode->i_sb, dbn);
+	err = 0;
 
-	set_buffer_uptodate(bh);
-	if (sdp->sd_args.ar_data == GFS2_DATA_ORDERED)
+	if (!buffer_mapped(bh)) {
+		gfs2_get_block(inode, iblock, bh, 0);
+		/* unmapped? It's a hole - nothing to do */
+		if (!buffer_mapped(bh))
+			goto unlock;
+	}
+
+	/* Ok, it's mapped. Make sure it's up-to-date */
+	if (PageUptodate(page))
+		set_buffer_uptodate(bh);
+
+	if (!buffer_uptodate(bh)) {
+		err = -EIO;
+		ll_rw_block(READ, 1, &bh);
+		wait_on_buffer(bh);
+		/* Uhhuh. Read error. Complain and punt. */
+		if (!buffer_uptodate(bh))
+			goto unlock;
+	}
+
+	if (sdp->sd_args.ar_data == GFS2_DATA_ORDERED/* || gfs2_is_jdata(ip)*/)
 		gfs2_trans_add_databuf(sdp, bh);
-	mark_buffer_dirty(bh);
 
- out:
+	kaddr = kmap_atomic(page, KM_USER0);
+	memset(kaddr + offset, 0, length);
+	flush_dcache_page(page);
+	kunmap_atomic(kaddr, KM_USER0);
+
+unlock:
 	unlock_page(page);
 	page_cache_release(page);
-
-	return error;
+	return err;
 }
 
-void gfs2_page_add_databufs(struct gfs2_sbd *sdp, struct page *page,
+void gfs2_page_add_databufs(struct gfs2_inode *ip, struct page *page,
 			    unsigned int from, unsigned int to)
 {
 	struct buffer_head *head = page_buffers(page);
@@ -267,7 +273,7 @@ void gfs2_page_add_databufs(struct gfs2_sbd *sdp, struct page *page,
 		end = start + bsize;
 		if (end <= from || start >= to)
 			continue;
-		gfs2_trans_add_databuf(sdp, bh);
+		gfs2_trans_add_databuf(ip->i_sbd, bh);
 	}
 }
 

fs/gfs2/page.h

@@ -16,8 +16,8 @@ void gfs2_page_sync(struct gfs2_glock *gl, int flags);
 
 int gfs2_unstuffer_page(struct gfs2_inode *ip, struct buffer_head *dibh,
 			uint64_t block, void *private);
-int gfs2_truncator_page(struct gfs2_inode *ip, uint64_t size);
-void gfs2_page_add_databufs(struct gfs2_sbd *sdp, struct page *page,
+int gfs2_block_truncate_page(struct address_space *mapping);
+void gfs2_page_add_databufs(struct gfs2_inode *ip, struct page *page,
 			    unsigned int from, unsigned int to);
 
 #endif /* __PAGE_DOT_H__ */