[PATCH] shm: add split function to shm_vm_ops

[Mike Kravetz]

The split function was added to vm_operations_struct to determine
if a mapping can be split.  This was mostly for device-dax and
hugetlbfs mappings which have specific alignment constraints.

mappings initiated via shmget/shmat have their original vm_ops
overwritten with shm_vm_ops.  shm_vm_ops functions will call back
to the original vm_ops if needed.  Add such a split function.

Fixes: 31383c6865a5 ("mm, hugetlbfs: introduce ->split() to vm_operations_struct)
Reported by: Laurent Dufour <ldufour@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
---
 ipc/shm.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/ipc/shm.c b/ipc/shm.c
index 7acda23430aa..50e88fc060b1 100644
--- a/ipc/shm.c
+++ b/ipc/shm.c
@@ -386,6 +386,17 @@ static int shm_fault(struct vm_fault *vmf)
 	return sfd->vm_ops->fault(vmf);
 }
 
+static int shm_split(struct vm_area_struct *vma, unsigned long addr)
+{
+	struct file *file = vma->vm_file;
+	struct shm_file_data *sfd = shm_file_data(file);
+
+	if (sfd->vm_ops && sfd->vm_ops->split)
+		return sfd->vm_ops->split(vma, addr);
+
+	return 0;
+}
+
 #ifdef CONFIG_NUMA
 static int shm_set_policy(struct vm_area_struct *vma, struct mempolicy *new)
 {
@@ -510,6 +521,7 @@ static const struct vm_operations_struct shm_vm_ops = {
 	.open	= shm_open,	/* callback for a new vm-area open */
 	.close	= shm_close,	/* callback for when the vm-area is released */
 	.fault	= shm_fault,
+	.split	= shm_split,
 #if defined(CONFIG_NUMA)
 	.set_policy = shm_set_policy,
 	.get_policy = shm_get_policy,
-- 
2.13.6