[PATCH 06/10] fs/xfs: transition from deprecated .mmap hook to .mmap_prepare

[Lorenzo Stoakes <lorenzo.stoakes@oracle.com>]

Since commit c84bf6dd2b83 ("mm: introduce new .mmap_prepare() file
callback"), the f_op->mmap() hook has been deprecated in favour of
f_op->mmap_prepare().

This callback is invoked in the mmap() logic far earlier, so error handling
can be performed more safely without complicated and bug-prone state
unwinding required should an error arise.

This hook also avoids passing a pointer to a not-yet-correctly-established
VMA avoiding any issues with referencing this data structure.

It rather provides a pointer to the new struct vm_area_desc descriptor type
which contains all required state and allows easy setting of required
parameters without any consideration needing to be paid to locking or
reference counts.

Note that nested filesystems like overlayfs are compatible with an
.mmap_prepare() callback since commit bb666b7c2707 ("mm: add mmap_prepare()
compatibility layer for nested file systems").

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 fs/xfs/xfs_file.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index ab97ce1f9087..f7b76647d675 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -1913,10 +1913,10 @@ static const struct vm_operations_struct xfs_file_vm_ops = {
 };
 
 STATIC int
-xfs_file_mmap(
-	struct file		*file,
-	struct vm_area_struct	*vma)
+xfs_file_mmap_prepare(
+	struct vm_area_desc *desc)
 {
+	struct file		*file = desc->file;
 	struct inode		*inode = file_inode(file);
 	struct xfs_buftarg	*target = xfs_inode_buftarg(XFS_I(inode));
 
@@ -1924,14 +1924,14 @@ xfs_file_mmap(
 	 * We don't support synchronous mappings for non-DAX files and
 	 * for DAX files if underneath dax_device is not synchronous.
 	 */
-	if (!daxdev_mapping_supported(vma->vm_flags, vma->vm_file,
+	if (!daxdev_mapping_supported(desc->vm_flags, file,
 				      target->bt_daxdev))
 		return -EOPNOTSUPP;
 
 	file_accessed(file);
-	vma->vm_ops = &xfs_file_vm_ops;
+	desc->vm_ops = &xfs_file_vm_ops;
 	if (IS_DAX(inode))
-		vm_flags_set(vma, VM_HUGEPAGE);
+		desc->vm_flags |= VM_HUGEPAGE;
 	return 0;
 }
 
@@ -1946,7 +1946,7 @@ const struct file_operations xfs_file_operations = {
 #ifdef CONFIG_COMPAT
 	.compat_ioctl	= xfs_file_compat_ioctl,
 #endif
-	.mmap		= xfs_file_mmap,
+	.mmap_prepare	= xfs_file_mmap_prepare,
 	.open		= xfs_file_open,
 	.release	= xfs_file_release,
 	.fsync		= xfs_file_fsync,
-- 
2.49.0