udf: Allocate blocks on write page fault

Currently if file with holes is mapped, udf allocates blocks for dirtied
pages during page writeback. This however creates problems when to
truncate final extent to proper size and currently we leave the last
extent untruncated which violates UDF standard. So allocate blocks on
write page fault instead. In that case the last extent gets truncated
the file is closed and everything is happy.
Signed-off-by: Jan Kara <jack@suse.cz>

fs/udf/file.c

@@ -134,6 +134,57 @@ const struct address_space_operations udf_adinicb_aops = {
 	.direct_IO	= udf_adinicb_direct_IO,
 };
 
+static vm_fault_t udf_page_mkwrite(struct vm_fault *vmf)
+{
+	struct vm_area_struct *vma = vmf->vma;
+	struct inode *inode = file_inode(vma->vm_file);
+	struct address_space *mapping = inode->i_mapping;
+	struct page *page = vmf->page;
+	loff_t size;
+	unsigned int end;
+	vm_fault_t ret = VM_FAULT_LOCKED;
+	int err;
+
+	sb_start_pagefault(inode->i_sb);
+	file_update_time(vma->vm_file);
+	filemap_invalidate_lock_shared(mapping);
+	lock_page(page);
+	size = i_size_read(inode);
+	if (page->mapping != inode->i_mapping || page_offset(page) >= size) {
+		unlock_page(page);
+		ret = VM_FAULT_NOPAGE;
+		goto out_unlock;
+	}
+	/* Space is already allocated for in-ICB file */
+	if (UDF_I(inode)->i_alloc_type == ICBTAG_FLAG_AD_IN_ICB)
+		goto out_dirty;
+	if (page->index == size >> PAGE_SHIFT)
+		end = size & ~PAGE_MASK;
+	else
+		end = PAGE_SIZE;
+	err = __block_write_begin(page, 0, end, udf_get_block);
+	if (!err)
+		err = block_commit_write(page, 0, end);
+	if (err < 0) {
+		unlock_page(page);
+		ret = block_page_mkwrite_return(err);
+		goto out_unlock;
+	}
+out_dirty:
+	set_page_dirty(page);
+	wait_for_stable_page(page);
+out_unlock:
+	filemap_invalidate_unlock_shared(mapping);
+	sb_end_pagefault(inode->i_sb);
+	return ret;
+}
+
+static const struct vm_operations_struct udf_file_vm_ops = {
+	.fault		= filemap_fault,
+	.map_pages	= filemap_map_pages,
+	.page_mkwrite	= udf_page_mkwrite,
+};
+
 static ssize_t udf_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	ssize_t retval;
@@ -238,11 +289,19 @@ static int udf_release_file(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+static int udf_file_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	file_accessed(file);
+	vma->vm_ops = &udf_file_vm_ops;
+
+	return 0;
+}
+
 const struct file_operations udf_file_operations = {
 	.read_iter		= generic_file_read_iter,
 	.unlocked_ioctl		= udf_ioctl,
 	.open			= generic_file_open,
-	.mmap			= generic_file_mmap,
+	.mmap			= udf_file_mmap,
 	.write_iter		= udf_file_write_iter,
 	.release		= udf_release_file,
 	.fsync			= generic_file_fsync,

fs/udf/inode.c

@@ -68,7 +68,6 @@ static void udf_prealloc_extents(struct inode *, int, int,
 static void udf_merge_extents(struct inode *, struct kernel_long_ad *, int *);
 static int udf_update_extents(struct inode *, struct kernel_long_ad *, int,
 			      int, struct extent_position *);
-static int udf_get_block(struct inode *, sector_t, struct buffer_head *, int);
 
 static void __udf_clear_extent_cache(struct inode *inode)
 {

fs/udf/udfdecl.h

@@ -160,6 +160,7 @@ extern void udf_evict_inode(struct inode *);
 extern int udf_write_inode(struct inode *, struct writeback_control *wbc);
 extern int8_t inode_bmap(struct inode *, sector_t, struct extent_position *,
 			 struct kernel_lb_addr *, uint32_t *, sector_t *);
+int udf_get_block(struct inode *, sector_t, struct buffer_head *, int);
 extern int udf_setup_indirect_aext(struct inode *inode, udf_pblk_t block,
 				   struct extent_position *epos);
 extern int __udf_add_aext(struct inode *inode, struct extent_position *epos,