[PATCH 05/10] mm: abstract vma_merge_new_vma() to use vma_merge_struct

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

Abstract this function to so we can write tests which use the newly
abstracted interface and maintain a stable interface for tests before/after
refactoring.

We introduce a temporary wrapper vma_merge_new_vma_wrapper() to minimise
the code changes, in a subsequent commit we will entirely refactor this
function.

We also introduce a temporary implementation of vma_merge_modified() for
the same reason - maintaining a common interface to the tests, this will be
removed when vma_merge_modified() is correctly implemented in a subsequent
commit.

Signed-off-by: Lorenzo Stoakes <lorenzo.stoakes@oracle.com>
---
 mm/mmap.c               |  6 +++---
 mm/vma.c                | 33 ++++++++++++---------------------
 mm/vma.h                | 33 ++++++++++++++++++++++++++++++---
 tools/testing/vma/vma.c | 12 ++++++++----
 4 files changed, 53 insertions(+), 31 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 04145347c245..f6593a81f73d 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1494,9 +1494,9 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 		 * vma again as we may succeed this time.
 		 */
 		if (unlikely(vm_flags != vma->vm_flags && prev)) {
-			merge = vma_merge_new_vma(&vmi, prev, vma,
-						  vma->vm_start, vma->vm_end,
-						  vma->vm_pgoff);
+			merge = vma_merge_new_vma_wrapper(&vmi, prev, vma,
+							  vma->vm_start, vma->vm_end,
+							  vma->vm_pgoff);
 			if (merge) {
 				/*
 				 * ->mmap() can change vma->vm_file and fput
diff --git a/mm/vma.c b/mm/vma.c
index 3d6ce04f1b9c..55615392e8d2 100644
--- a/mm/vma.c
+++ b/mm/vma.c
@@ -1106,6 +1106,11 @@ static struct vm_area_struct *vma_merge(struct vma_merge_struct *vmg)
 	return NULL;
 }

+struct vm_area_struct *vma_merge_modified(struct vma_merge_struct *vmg)
+{
+	return vma_merge(vmg);
+}
+
 /*
  * We are about to modify one or multiple of a VMA's flags, policy, userfaultfd
  * context and anonymous VMA name within the range [start, end).
@@ -1260,27 +1265,14 @@ struct vm_area_struct
  * Attempt to merge a newly mapped VMA with those adjacent to it. The caller
  * must ensure that [start, end) does not overlap any existing VMA.
  */
-struct vm_area_struct
-*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
-		   struct vm_area_struct *vma, unsigned long start,
-		   unsigned long end, pgoff_t pgoff)
+struct vm_area_struct *vma_merge_new_vma(struct vma_merge_struct *vmg)
 {
-	struct vma_merge_struct vmg = {
-		.vmi = vmi,
-		.prev = prev,
-		.vma = vma,
-		.start = start,
-		.end = end,
-		.flags = vma->vm_flags,
-		.file = vma->vm_file,
-		.anon_vma = vma->anon_vma,
-		.pgoff = pgoff,
-		.policy = vma_policy(vma),
-		.uffd_ctx = vma->vm_userfaultfd_ctx,
-		.anon_name = anon_vma_name(vma),
-	};
+	if (!vmg->prev) {
+		vmg->prev = vma_prev(vmg->vmi);
+		vma_iter_set(vmg->vmi, vmg->start);
+	}

-	return vma_merge(&vmg);
+	return vma_merge(vmg);
 }

 /*
@@ -1295,7 +1287,6 @@ struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
 	struct vma_merge_struct vmg = {
 		.vmi = vmi,
 		.prev = vma,
-		.vma = vma,
 		.start = vma->vm_end,
 		.end = vma->vm_end + delta,
 		.flags = vma->vm_flags,
@@ -1425,7 +1416,7 @@ struct vm_area_struct *copy_vma(struct vm_area_struct **vmap,
 	if (new_vma && new_vma->vm_start < addr + len)
 		return NULL;	/* should never get here */

-	new_vma = vma_merge_new_vma(&vmi, prev, vma, addr, addr + len, pgoff);
+	new_vma = vma_merge_new_vma_wrapper(&vmi, prev, vma, addr, addr + len, pgoff);
 	if (new_vma) {
 		/*
 		 * Source vma may have been merged into new_vma
diff --git a/mm/vma.h b/mm/vma.h
index c464d25da120..50459f9e4c7f 100644
--- a/mm/vma.h
+++ b/mm/vma.h
@@ -134,9 +134,36 @@ struct vm_area_struct
 		       struct vm_userfaultfd_ctx new_ctx);

 struct vm_area_struct
-*vma_merge_new_vma(struct vma_iterator *vmi, struct vm_area_struct *prev,
-		   struct vm_area_struct *vma, unsigned long start,
-		   unsigned long end, pgoff_t pgoff);
+*vma_merge_new_vma(struct vma_merge_struct *vmg);
+
+/* Temporary convenience wrapper. */
+static inline struct vm_area_struct
+*vma_merge_new_vma_wrapper(struct vma_iterator *vmi, struct vm_area_struct *prev,
+			   struct vm_area_struct *vma, unsigned long start,
+			   unsigned long end, pgoff_t pgoff)
+{
+	struct vma_merge_struct vmg = {
+		.vmi = vmi,
+		.prev = prev,
+		.start = start,
+		.end = end,
+		.flags = vma->vm_flags,
+		.file = vma->vm_file,
+		.anon_vma = vma->anon_vma,
+		.pgoff = pgoff,
+		.policy = vma_policy(vma),
+		.uffd_ctx = vma->vm_userfaultfd_ctx,
+		.anon_name = anon_vma_name(vma),
+	};
+
+	return vma_merge_new_vma(&vmg);
+}
+
+/*
+ * Temporary wrapper around vma_merge() so we can have a common interface for
+ * tests.
+ */
+struct vm_area_struct *vma_merge_modified(struct vma_merge_struct *vmg);

 struct vm_area_struct *vma_merge_extend(struct vma_iterator *vmi,
 					struct vm_area_struct *vma,
diff --git a/tools/testing/vma/vma.c b/tools/testing/vma/vma.c
index d216e51206c1..4416cfa93056 100644
--- a/tools/testing/vma/vma.c
+++ b/tools/testing/vma/vma.c
@@ -53,16 +53,20 @@ static bool test_simple_merge(void)
 	unsigned long flags = VM_READ | VM_WRITE | VM_MAYREAD | VM_MAYWRITE;
 	struct mm_struct mm = {};
 	struct vm_area_struct *vma_left = alloc_vma(&mm, 0, 0x1000, 0, flags);
-	struct vm_area_struct *vma_middle = alloc_vma(&mm, 0x1000, 0x2000, 1, flags);
 	struct vm_area_struct *vma_right = alloc_vma(&mm, 0x2000, 0x3000, 2, flags);
 	VMA_ITERATOR(vmi, &mm, 0x1000);
+	struct vma_merge_struct vmg = {
+		.vmi = &vmi,
+		.start = 0x1000,
+		.end = 0x2000,
+		.flags = flags,
+		.pgoff = 1,
+	};

 	ASSERT_FALSE(vma_link(&mm, vma_left));
-	ASSERT_FALSE(vma_link(&mm, vma_middle));
 	ASSERT_FALSE(vma_link(&mm, vma_right));

-	vma = vma_merge_new_vma(&vmi, vma_left, vma_middle, 0x1000,
-				0x2000, 1);
+	vma = vma_merge_new_vma(&vmg);
 	ASSERT_NE(vma, NULL);

 	ASSERT_EQ(vma->vm_start, 0);
--
2.45.2