[RFC PATCH 2/7] dax: copy data before write.

[Shiyang Ruan <ruansy.fnst@xxxxxxxxxxxxxx>]

Add dax_copy_edges() into each dax actor functions to perform COW in the
case of IOMAP_COW type is set.

Signed-off-by: Shiyang Ruan <ruansy.fnst@xxxxxxxxxxxxxx>
---
 fs/dax.c | 39 +++++++++++++++++++++++++++++++++------
 1 file changed, 33 insertions(+), 6 deletions(-)

diff --git a/fs/dax.c b/fs/dax.c
index 450baafe2ea4..084cc21d47a4 100644
--- a/fs/dax.c
+++ b/fs/dax.c
@@ -1098,11 +1098,12 @@ EXPORT_SYMBOL_GPL(__dax_zero_page_range);
  * 		    offset/offset+length are not page aligned.
  */
 static int dax_copy_edges(struct inode *inode, loff_t pos, loff_t length,
-			  struct iomap *srcmap, void *daddr)
+			  struct iomap *srcmap, void *daddr, bool pmd)
 {
-	unsigned offset = pos & (PAGE_SIZE - 1);
+	size_t page_size = pmd ? PMD_SIZE : PAGE_SIZE;
+	unsigned offset = pos & (page_size - 1);
 	loff_t end = pos + length;
-	loff_t pg_end = round_up(end, PAGE_SIZE);
+	loff_t pg_end = round_up(end, page_size);
 	void *saddr = 0;
 	int ret = 0;
 
@@ -1153,7 +1154,8 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 			return iov_iter_zero(min(length, end - pos), iter);
 	}
 
-	if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED))
+	if (WARN_ON_ONCE(iomap->type != IOMAP_MAPPED &&
+			 iomap->type != IOMAP_COW))
 		return -EIO;
 
 	/*
@@ -1192,6 +1194,13 @@ dax_iomap_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
 			break;
 		}
 
+		if (iomap->type == IOMAP_COW) {
+			ret = dax_copy_edges(inode, pos, length, srcmap, kaddr,
+					     false);
+			if (ret)
+				break;
+		}
+
 		map_len = PFN_PHYS(map_len);
 		kaddr += offset;
 		map_len -= offset;
@@ -1300,6 +1309,7 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	vm_fault_t ret = 0;
 	void *entry;
 	pfn_t pfn;
+	void *kaddr;
 
 	trace_dax_pte_fault(inode, vmf, ret);
 	/*
@@ -1380,19 +1390,27 @@ static vm_fault_t dax_iomap_pte_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	sync = dax_fault_is_synchronous(flags, vma, &iomap);
 
 	switch (iomap.type) {
+	case IOMAP_COW:
 	case IOMAP_MAPPED:
 		if (iomap.flags & IOMAP_F_NEW) {
 			count_vm_event(PGMAJFAULT);
 			count_memcg_event_mm(vma->vm_mm, PGMAJFAULT);
 			major = VM_FAULT_MAJOR;
 		}
-		error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn, NULL);
+		error = dax_iomap_pfn(&iomap, pos, PAGE_SIZE, &pfn, &kaddr);
 		if (error < 0)
 			goto error_finish_iomap;
 
 		entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
 						 0, write && !sync);
 
+		if (iomap.type == IOMAP_COW) {
+			error = dax_copy_edges(inode, pos, PAGE_SIZE, &srcmap,
+					       kaddr, false);
+			if (error)
+				goto error_finish_iomap;
+		}
+
 		/*
 		 * If we are doing synchronous page fault and inode needs fsync,
 		 * we can insert PTE into page tables only after that happens.
@@ -1523,6 +1541,7 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	loff_t pos;
 	int error;
 	pfn_t pfn;
+	void *kaddr;
 
 	/*
 	 * Check whether offset isn't beyond end of file now. Caller is
@@ -1602,14 +1621,22 @@ static vm_fault_t dax_iomap_pmd_fault(struct vm_fault *vmf, pfn_t *pfnp,
 	sync = dax_fault_is_synchronous(iomap_flags, vma, &iomap);
 
 	switch (iomap.type) {
+	case IOMAP_COW:
 	case IOMAP_MAPPED:
-		error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn, NULL);
+		error = dax_iomap_pfn(&iomap, pos, PMD_SIZE, &pfn, &kaddr);
 		if (error < 0)
 			goto finish_iomap;
 
 		entry = dax_insert_entry(&xas, mapping, vmf, entry, pfn,
 						DAX_PMD, write && !sync);
 
+		if (iomap.type == IOMAP_COW) {
+			error = dax_copy_edges(inode, pos, PMD_SIZE, &srcmap,
+					       kaddr, true);
+			if (error)
+				goto unlock_entry;
+		}
+
 		/*
 		 * If we are doing synchronous page fault and inode needs fsync,
 		 * we can insert PMD into page tables only after that happens.
-- 
2.17.0