mm: use new return type vm_fault_t

Use new return type vm_fault_t for fault handler in struct
vm_operations_struct.  For now, this is just documenting that the
function returns a VM_FAULT value rather than an errno.  Once all
instances are converted, vm_fault_t will become a distinct type.

Link: http://lkml.kernel.org/r/20180511190542.GA2412@jordon-HP-15-Notebook-PCSigned-off-by: Souptick Joarder <jrdr.linux@gmail.com>
Reviewed-by: Matthew Wilcox <mawilcox@microsoft.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Jan Kara <jack@suse.cz>
Cc: Ross Zwisler <ross.zwisler@linux.intel.com>
Cc: Rik van Riel <riel@redhat.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Hugh Dickins <hughd@google.com>
Cc: Pavel Tatashin <pasha.tatashin@oracle.com>
Cc: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mm.h

@@ -2303,10 +2303,10 @@ extern void truncate_inode_pages_range(struct address_space *,
 extern void truncate_inode_pages_final(struct address_space *);
 
 /* generic vm_area_ops exported for stackable file systems */
-extern int filemap_fault(struct vm_fault *vmf);
+extern vm_fault_t filemap_fault(struct vm_fault *vmf);
 extern void filemap_map_pages(struct vm_fault *vmf,
 		pgoff_t start_pgoff, pgoff_t end_pgoff);
-extern int filemap_page_mkwrite(struct vm_fault *vmf);
+extern vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf);
 
 /* mm/page-writeback.c */
 int __must_check write_one_page(struct page *page);

mm/filemap.c

@@ -2489,7 +2489,7 @@ static void do_async_mmap_readahead(struct vm_area_struct *vma,
  *
  * We never return with VM_FAULT_RETRY and a bit from VM_FAULT_ERROR set.
  */
-int filemap_fault(struct vm_fault *vmf)
+vm_fault_t filemap_fault(struct vm_fault *vmf)
 {
 	int error;
 	struct file *file = vmf->vma->vm_file;
@@ -2499,7 +2499,7 @@ int filemap_fault(struct vm_fault *vmf)
 	pgoff_t offset = vmf->pgoff;
 	pgoff_t max_off;
 	struct page *page;
-	int ret = 0;
+	vm_fault_t ret = 0;
 
 	max_off = DIV_ROUND_UP(i_size_read(inode), PAGE_SIZE);
 	if (unlikely(offset >= max_off))
@@ -2693,11 +2693,11 @@ void filemap_map_pages(struct vm_fault *vmf,
 }
 EXPORT_SYMBOL(filemap_map_pages);
 
-int filemap_page_mkwrite(struct vm_fault *vmf)
+vm_fault_t filemap_page_mkwrite(struct vm_fault *vmf)
 {
 	struct page *page = vmf->page;
 	struct inode *inode = file_inode(vmf->vma->vm_file);
-	int ret = VM_FAULT_LOCKED;
+	vm_fault_t ret = VM_FAULT_LOCKED;
 
 	sb_start_pagefault(inode->i_sb);
 	file_update_time(vmf->vma->vm_file);

mm/nommu.c

@@ -1763,7 +1763,7 @@ unsigned long arch_get_unmapped_area(struct file *file, unsigned long addr,
 	return -ENOMEM;
 }
 
-int filemap_fault(struct vm_fault *vmf)
+vm_fault_t filemap_fault(struct vm_fault *vmf)
 {
 	BUG();
 	return 0;