mm: Make default vm_ops provide ->page_mkwrite handler

Make default vm_ops provide ->page_mkwrite handler. Currently it only updates
file's modification times and gets locked page but later it will also handle
filesystem freezing.

BugLink: https://bugs.launchpad.net/bugs/897421
Tested-by: Kamal Mostafa <kamal@canonical.com>
Tested-by: Peter M. Petrakis <peter.petrakis@canonical.com>
Tested-by: Dann Frazier <dann.frazier@canonical.com>
Tested-by: Massimo Morana <massimo.morana@canonical.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 21 insertions, 0 deletions

diff --git a/include/linux/mm.h b/include/linux/mm.h
index b36d08ce5c57..15987d8e1d59 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -1411,6 +1411,7 @@ extern void truncate_inode_pages_range(struct address_space *,
 
 /* generic vm_area_ops exported for stackable file systems */
 extern int filemap_fault(struct vm_area_struct *, struct vm_fault *);
+extern int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf);
 
 /* mm/page-writeback.c */
 int write_one_page(struct page *page, int wait);
diff --git a/mm/filemap.c b/mm/filemap.c
index a4a5260b0279..51efee65c2cc 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -1712,8 +1712,27 @@ page_not_uptodate:
 }
 EXPORT_SYMBOL(filemap_fault);
 
+int filemap_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf)
+{
+        struct page *page = vmf->page;
+        struct inode *inode = vma->vm_file->f_path.dentry->d_inode;
+        int ret = VM_FAULT_LOCKED;
+
+        file_update_time(vma->vm_file);
+        lock_page(page);
+        if (page->mapping != inode->i_mapping) {
+                unlock_page(page);
+                ret = VM_FAULT_NOPAGE;
+                goto out;
+        }
+out:
+        return ret;
+}
+EXPORT_SYMBOL(filemap_page_mkwrite);
+
 const struct vm_operations_struct generic_file_vm_ops = {
         .fault          = filemap_fault,
+        .page_mkwrite   = filemap_page_mkwrite,
 };
 
 /* This is used for a general mmap of a disk file */
diff --git a/mm/filemap_xip.c b/mm/filemap_xip.c
index 213ca1f53409..80b34ef82dfe 100644
--- a/mm/filemap_xip.c
+++ b/mm/filemap_xip.c
@@ -304,6 +304,7 @@ out:
 
 static const struct vm_operations_struct xip_file_vm_ops = {
         .fault  = xip_file_fault,
+        .page_mkwrite   = filemap_page_mkwrite,
 };
 
 int xip_file_mmap(struct file * file, struct vm_area_struct * vma)