[PATCH v2 21/23] xfs: handle merkle tree block size != fs blocksize != PAGE_SIZE

[Andrey Albershteyn <aalbersh@xxxxxxxxxx>]

In case of different Merkle tree block size fs-verity expects
->read_merkle_tree_page() to return Merkle tree page filled with
Merkle tree blocks. The XFS stores each merkle tree block under
extended attribute. Those attributes are addressed by block offset
into Merkle tree.

This patch make ->read_merkle_tree_page() to fetch multiple merkle
tree blocks based on size ratio. Also the reference to each xfs_buf
is passed with page->private to ->drop_page().

Signed-off-by: Andrey Albershteyn <aalbersh@xxxxxxxxxx>
---
 fs/xfs/xfs_verity.c | 74 +++++++++++++++++++++++++++++++++++----------
 fs/xfs/xfs_verity.h |  8 +++++
 2 files changed, 66 insertions(+), 16 deletions(-)

diff --git a/fs/xfs/xfs_verity.c b/fs/xfs/xfs_verity.c
index a9874ff4efcd..ef0aff216f06 100644
--- a/fs/xfs/xfs_verity.c
+++ b/fs/xfs/xfs_verity.c
@@ -134,6 +134,10 @@ xfs_read_merkle_tree_page(
 	struct page		*page = NULL;
 	__be64			name = cpu_to_be64(index << PAGE_SHIFT);
 	uint32_t		bs = 1 << log_blocksize;
+	int			blocks_per_page =
+		(1 << (PAGE_SHIFT - log_blocksize));
+	int			n = 0;
+	int			offset = 0;
 	struct xfs_da_args	args = {
 		.dp		= ip,
 		.attr_filter	= XFS_ATTR_VERITY,
@@ -143,26 +147,59 @@ xfs_read_merkle_tree_page(
 		.valuelen	= bs,
 	};
 	int			error = 0;
+	bool			is_checked = true;
+	struct xfs_verity_buf_list	*buf_list;
 
 	page = alloc_page(GFP_KERNEL);
 	if (!page)
 		return ERR_PTR(-ENOMEM);
 
-	error = xfs_attr_get(&args);
-	if (error) {
-		kmem_free(args.value);
-		xfs_buf_rele(args.bp);
+	buf_list = kzalloc(sizeof(struct xfs_verity_buf_list), GFP_KERNEL);
+	if (!buf_list) {
 		put_page(page);
-		return ERR_PTR(-EFAULT);
+		return ERR_PTR(-ENOMEM);
 	}
 
-	if (args.bp->b_flags & XBF_VERITY_CHECKED)
+	/*
+	 * Fill the page with Merkle tree blocks. The blcoks_per_page is higher
+	 * than 1 when fs block size != PAGE_SIZE or Merkle tree block size !=
+	 * PAGE SIZE
+	 */
+	for (n = 0; n < blocks_per_page; n++) {
+		offset = bs * n;
+		name = cpu_to_be64(((index << PAGE_SHIFT) + offset));
+		args.name = (const uint8_t *)&name;
+
+		error = xfs_attr_get(&args);
+		if (error) {
+			kmem_free(args.value);
+			/*
+			 * No more Merkle tree blocks (e.g. this was the last
+			 * block of the tree)
+			 */
+			if (error == -ENOATTR)
+				break;
+			xfs_buf_rele(args.bp);
+			put_page(page);
+			kmem_free(buf_list);
+			return ERR_PTR(-EFAULT);
+		}
+
+		buf_list->bufs[buf_list->buf_count++] = args.bp;
+
+		/* One of the buffers was dropped */
+		if (!(args.bp->b_flags & XBF_VERITY_CHECKED))
+			is_checked = false;
+
+		memcpy(page_address(page) + offset, args.value, args.valuelen);
+		kmem_free(args.value);
+		args.value = NULL;
+	}
+
+	if (is_checked)
 		SetPageChecked(page);
+	page->private = (unsigned long)buf_list;
 
-	page->private = (unsigned long)args.bp;
-	memcpy(page_address(page), args.value, args.valuelen);
-
-	kmem_free(args.value);
 	return page;
 }
 
@@ -191,16 +228,21 @@ xfs_write_merkle_tree_block(
 
 static void
 xfs_drop_page(
-	struct page	*page)
+	struct page			*page)
 {
-	struct xfs_buf *buf = (struct xfs_buf *)page->private;
+	int				i = 0;
+	struct xfs_verity_buf_list	*buf_list =
+		(struct xfs_verity_buf_list *)page->private;
 
-	ASSERT(buf != NULL);
+	ASSERT(buf_list != NULL);
 
-	if (PageChecked(page))
-		buf->b_flags |= XBF_VERITY_CHECKED;
+	for (i = 0; i < buf_list->buf_count; i++) {
+		if (PageChecked(page))
+			buf_list->bufs[i]->b_flags |= XBF_VERITY_CHECKED;
+		xfs_buf_rele(buf_list->bufs[i]);
+	}
 
-	xfs_buf_rele(buf);
+	kmem_free(buf_list);
 	put_page(page);
 }
 
diff --git a/fs/xfs/xfs_verity.h b/fs/xfs/xfs_verity.h
index ae5d87ca32a8..433b2f4ae3bc 100644
--- a/fs/xfs/xfs_verity.h
+++ b/fs/xfs/xfs_verity.h
@@ -16,4 +16,12 @@ extern const struct fsverity_operations xfs_verity_ops;
 #define xfs_verity_ops NULL
 #endif	/* CONFIG_FS_VERITY */
 
+/* Minimal Merkle tree block size is 1024 */
+#define XFS_VERITY_MAX_MBLOCKS_PER_PAGE (1 << (PAGE_SHIFT - 10))
+
+struct xfs_verity_buf_list {
+	unsigned int	buf_count;
+	struct xfs_buf	*bufs[XFS_VERITY_MAX_MBLOCKS_PER_PAGE];
+};
+
 #endif	/* __XFS_VERITY_H__ */
-- 
2.38.4