[RFC 11/11] ext4: add ext4_dax_pfn_mkwrite()

[Ross Zwisler <ross.zwisler@linux.intel.com>]

Add ext4_dax_pfn_mkwrite() that properly protects against freeze, sets
the file update time and calls into dax_pfn_mkwrite() to add the newly
dirtied page to the radix tree which tracks dirty DAX pages.

Signed-off-by: Ross Zwisler <ross.zwisler@linux.intel.com>
---
 fs/ext4/file.c | 22 +++++++++++++++++++++-
 1 file changed, 21 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 54d7729..7f62cad 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -272,11 +272,31 @@ static int ext4_dax_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
 				ext4_end_io_unwritten);
 }
 
+static int ext4_dax_pfn_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+	struct inode *inode = file_inode(vma->vm_file);
+	loff_t size;
+	int ret;
+
+	sb_start_pagefault(inode->i_sb);
+	file_update_time(vma->vm_file);
+
+	/* check that the faulting page hasn't raced with truncate */
+	size = (i_size_read(inode) + PAGE_SIZE - 1) >> PAGE_SHIFT;
+	if (vmf->pgoff >= size)
+		ret = VM_FAULT_SIGBUS;
+	else
+		ret = dax_pfn_mkwrite(vma, vmf);
+
+	sb_end_pagefault(inode->i_sb);
+	return ret;
+}
+
 static const struct vm_operations_struct ext4_dax_vm_ops = {
 	.fault		= ext4_dax_fault,
 	.pmd_fault	= ext4_dax_pmd_fault,
 	.page_mkwrite	= ext4_dax_mkwrite,
-	.pfn_mkwrite	= dax_pfn_mkwrite,
+	.pfn_mkwrite	= ext4_dax_pfn_mkwrite,
 };
 #else
 #define ext4_dax_vm_ops	ext4_file_vm_ops
-- 
2.1.0