[PATCH 11/18] btrfs: add dax mmap support

[Goldwyn Rodrigues <rgoldwyn@xxxxxxx>]

From: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>

Add a new vm_operations struct btrfs_dax_vm_ops
specifically for dax files.

Since we will be removing(nulling) readpages/writepages for dax
return ENOEXEC only for non-dax files.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@xxxxxxxx>
---
 fs/btrfs/ctree.h |  1 +
 fs/btrfs/dax.c   | 13 ++++++++++++-
 fs/btrfs/file.c  | 18 ++++++++++++++++--
 3 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index eec01eb92f33..2b7bdabb44f8 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3802,6 +3802,7 @@ int btree_readahead_hook(struct extent_buffer *eb, int err);
 /* dax.c */
 ssize_t btrfs_file_dax_read(struct kiocb *iocb, struct iov_iter *to);
 ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *from);
+vm_fault_t btrfs_dax_fault(struct vm_fault *vmf);
 #else
 static inline ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *from)
 {
diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
index f5cc9bcdbf14..de957d681e16 100644
--- a/fs/btrfs/dax.c
+++ b/fs/btrfs/dax.c
@@ -139,7 +139,7 @@ static int btrfs_iomap_begin(struct inode *inode, loff_t pos,
 
 	iomap->addr = em->block_start + diff;
 	/* Check if we really need to copy data from old extent */
-	if (bi && !bi->nocow && (offset || pos + length < bi->end)) {
+	if (bi && !bi->nocow && (offset || pos + length < bi->end || flags & IOMAP_FAULT)) {
 		iomap->type = IOMAP_DAX_COW;
 		if (srcblk) {
 			sector_t sector = (srcblk + (pos & PAGE_MASK) -
@@ -216,4 +216,15 @@ ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct iov_iter *iter)
 	}
 	return ret;
 }
+
+vm_fault_t btrfs_dax_fault(struct vm_fault *vmf)
+{
+	vm_fault_t ret;
+	pfn_t pfn;
+	ret = dax_iomap_fault(vmf, PE_SIZE_PTE, &pfn, NULL, &btrfs_iomap_ops);
+	if (ret & VM_FAULT_NEEDDSYNC)
+		ret = dax_finish_sync_fault(vmf, PE_SIZE_PTE, pfn);
+
+	return ret;
+}
 #endif /* CONFIG_FS_DAX */
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index a795023e26ca..9d5a3c99a6b9 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2214,15 +2214,29 @@ static const struct vm_operations_struct btrfs_file_vm_ops = {
 	.page_mkwrite	= btrfs_page_mkwrite,
 };
 
+#ifdef CONFIG_FS_DAX
+static const struct vm_operations_struct btrfs_dax_vm_ops = {
+	.fault          = btrfs_dax_fault,
+	.page_mkwrite   = btrfs_dax_fault,
+	.pfn_mkwrite    = btrfs_dax_fault,
+};
+#else
+#define btrfs_dax_vm_ops btrfs_file_vm_ops
+#endif
+
 static int btrfs_file_mmap(struct file	*filp, struct vm_area_struct *vma)
 {
 	struct address_space *mapping = filp->f_mapping;
+	struct inode *inode = file_inode(filp);
 
-	if (!mapping->a_ops->readpage)
+	if (!IS_DAX(inode) && !mapping->a_ops->readpage)
 		return -ENOEXEC;
 
 	file_accessed(filp);
-	vma->vm_ops = &btrfs_file_vm_ops;
+	if (IS_DAX(inode))
+		vma->vm_ops = &btrfs_dax_vm_ops;
+	else
+		vma->vm_ops = &btrfs_file_vm_ops;
 
 	return 0;
 }
-- 
2.16.4