[PATCH 08/10] btrfs: dax add read mmap path

[Goldwyn Rodrigues]

From: Goldwyn Rodrigues <rgold...@suse.com>

Signed-off-by: Goldwyn Rodrigues <rgold...@suse.com>
---
 fs/btrfs/ctree.h |  1 +
 fs/btrfs/dax.c   | 43 +++++++++++++++++++++++++++++++++++++++++++
 fs/btrfs/file.c  | 12 +++++++++++-
 3 files changed, 55 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index d91ff283a966..33648121ca52 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3694,6 +3694,7 @@ 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);
 #endif /* CONFIG_FS_DAX */
 
 static inline int is_fstree(u64 rootid)
diff --git a/fs/btrfs/dax.c b/fs/btrfs/dax.c
index 4000259a426c..88017f8799d1 100644
--- a/fs/btrfs/dax.c
+++ b/fs/btrfs/dax.c
@@ -190,5 +190,48 @@ ssize_t btrfs_file_dax_write(struct kiocb *iocb, struct 
iov_iter *from)
                                count - done, true);
        extent_changeset_free(data_reserved);
         return done ? done : ret;
+}
+
+/* As copied from dax_iomap_pte_fault() */
+vm_fault_t btrfs_dax_fault(struct vm_fault *vmf)
+{
+       pfn_t pfn;
+       struct address_space *mapping = vmf->vma->vm_file->f_mapping;
+       XA_STATE(xas, &mapping->i_pages, vmf->pgoff);
+       struct inode *inode = mapping->host;
+       loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
+       void *entry = NULL;
+       vm_fault_t ret = 0;
+
+       if (pos > i_size_read(inode)) {
+               ret = VM_FAULT_SIGBUS;
+               goto out;
+       }
 
+       entry = grab_mapping_entry(&xas, mapping, 0);
+       if (IS_ERR(entry)) {
+               ret = dax_fault_return(PTR_ERR(entry));
+               goto out;
+       }
+
+       if (!vmf->cow_page) {
+               sector_t sector;
+               struct extent_map *em;
+                em = btrfs_get_extent(BTRFS_I(inode), NULL, 0, pos, PAGE_SIZE, 
0);
+               if (em->block_start == EXTENT_MAP_HOLE) {
+                       ret = dax_load_hole(&xas, mapping, entry, vmf);
+                       goto out;
+               }
+               sector = ((get_start_sect(em->bdev) << 9) +
+                         (em->block_start + (pos - em->start))) >> 9;
+               ret = dax_pfn(fs_dax_get_by_bdev(em->bdev), em->bdev, sector, 
PAGE_SIZE, &pfn);
+               if (ret)
+                       goto out;
+               dax_insert_entry(&xas, mapping, vmf, entry, pfn, 0, false);
+               ret = vmf_insert_mixed(vmf->vma, vmf->address, pfn);
+       }
+out:
+       if (entry)
+               dax_unlock_entry(&xas, entry);
+       return ret;
 }
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index 29a3b12e6660..38b494686fb2 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2227,8 +2227,18 @@ int btrfs_sync_file(struct file *file, loff_t start, 
loff_t end, int datasync)
        return ret > 0 ? -EIO : ret;
 }
 
+static vm_fault_t btrfs_fault(struct vm_fault *vmf)
+{
+       struct inode *inode = vmf->vma->vm_file->f_mapping->host;
+#ifdef CONFIG_FS_DAX
+       if (IS_DAX(inode))
+               return btrfs_dax_fault(vmf);
+#endif
+       return filemap_fault(vmf);
+}
+
 static const struct vm_operations_struct btrfs_file_vm_ops = {
-       .fault          = filemap_fault,
+       .fault          = btrfs_fault,
        .map_pages      = filemap_map_pages,
        .page_mkwrite   = btrfs_page_mkwrite,
 };
-- 
2.16.4