dax: Introduce IOMAP_FAULT flag

Introduce a flag telling iomap operations whether they are handling a
fault or other IO. That may influence behavior wrt inode size and
similar things.

Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/dax.c

@@ -1266,7 +1266,7 @@ int dax_iomap_fault(struct vm_area_struct *vma, struct vm_fault *vmf,
 	loff_t pos = (loff_t)vmf->pgoff << PAGE_SHIFT;
 	sector_t sector;
 	struct iomap iomap = { 0 };
-	unsigned flags = 0;
+	unsigned flags = IOMAP_FAULT;
 	int error, major = 0;
 	int locked_status = 0;
 	void *entry;
@@ -1467,7 +1467,7 @@ int dax_iomap_pmd_fault(struct vm_area_struct *vma, unsigned long address,
 	struct address_space *mapping = vma->vm_file->f_mapping;
 	unsigned long pmd_addr = address & PMD_MASK;
 	bool write = flags & FAULT_FLAG_WRITE;
-	unsigned int iomap_flags = write ? IOMAP_WRITE : 0;
+	unsigned int iomap_flags = (write ? IOMAP_WRITE : 0) | IOMAP_FAULT;
 	struct inode *inode = mapping->host;
 	int result = VM_FAULT_FALLBACK;
 	struct iomap iomap = { 0 };

fs/iomap.c

@@ -468,8 +468,9 @@ int iomap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
 
 	offset = page_offset(page);
 	while (length > 0) {
-		ret = iomap_apply(inode, offset, length, IOMAP_WRITE,
-				ops, page, iomap_page_mkwrite_actor);
+		ret = iomap_apply(inode, offset, length,
+				IOMAP_WRITE | IOMAP_FAULT, ops, page,
+				iomap_page_mkwrite_actor);
 		if (unlikely(ret <= 0))
 			goto out_unlock;
 		offset += ret;

include/linux/iomap.h

@@ -44,6 +44,7 @@ struct iomap {
  */
 #define IOMAP_WRITE		(1 << 0)
 #define IOMAP_ZERO		(1 << 1)
+#define IOMAP_FAULT		(1 << 3) /* mapping for page fault */
 
 struct iomap_ops {
 	/*