xfs: use shmem_get_folio in xfile_obj_store

Switch to using shmem_get_folio and manually dirtying the page instead
of abusing aops->write_begin and aops->write_end in xfile_get_page.

This simplifies the code by not doing indirect calls of not actually
exported interfaces that don't really fit the use case very well, and
happens to get us large folio support for free.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Chandan Babu R <chandanbabu@kernel.org>

fs/xfs/scrub/xfile.c

@@ -183,11 +183,7 @@ xfile_store(
 	loff_t			pos)
 {
 	struct inode		*inode = file_inode(xf->file);
-	struct address_space	*mapping = inode->i_mapping;
-	const struct address_space_operations *aops = mapping->a_ops;
-	struct page		*page = NULL;
 	unsigned int		pflags;
-	int			error = 0;
 
 	if (count > MAX_RW_COUNT)
 		return -ENOMEM;
@@ -196,60 +192,45 @@ xfile_store(
 
 	trace_xfile_store(xf, pos, count);
 
+	/*
+	 * Increase the file size first so that shmem_get_folio(..., SGP_CACHE),
+	 * actually allocates a folio instead of erroring out.
+	 */
+	if (pos + count > i_size_read(inode))
+		i_size_write(inode, pos + count);
+
 	pflags = memalloc_nofs_save();
 	while (count > 0) {
-		void		*fsdata = NULL;
-		void		*p, *kaddr;
+		struct folio	*folio;
 		unsigned int	len;
-		int		ret;
+		unsigned int	offset;
 
-		len = min_t(ssize_t, count, PAGE_SIZE - offset_in_page(pos));
-
-		/*
-		 * We call write_begin directly here to avoid all the freezer
-		 * protection lock-taking that happens in the normal path.
-		 * shmem doesn't support fs freeze, but lockdep doesn't know
-		 * that and will trip over that.
-		 */
-		error = aops->write_begin(NULL, mapping, pos, len, &page,
-				&fsdata);
-		if (error) {
-			error = -ENOMEM;
+		if (shmem_get_folio(inode, pos >> PAGE_SHIFT, &folio,
+				SGP_CACHE) < 0)
 			break;
-		}
-
-		/*
-		 * xfile pages must never be mapped into userspace, so we skip
-		 * the dcache flush.  If the page is not uptodate, zero it
-		 * before writing data.
-		 */
-		kaddr = page_address(page);
-		if (!PageUptodate(page)) {
-			memset(kaddr, 0, PAGE_SIZE);
-			SetPageUptodate(page);
-		}
-		p = kaddr + offset_in_page(pos);
-		memcpy(p, buf, len);
-
-		ret = aops->write_end(NULL, mapping, pos, len, len, page,
-				fsdata);
-		if (ret < 0) {
-			error = -ENOMEM;
+		if (filemap_check_wb_err(inode->i_mapping, 0)) {
+			folio_unlock(folio);
+			folio_put(folio);
 			break;
 		}
 
-		if (ret != len) {
-			error = -ENOMEM;
-			break;
-		}
+		offset = offset_in_folio(folio, pos);
+		len = min_t(ssize_t, count, folio_size(folio) - offset);
+		memcpy(folio_address(folio) + offset, buf, len);
+
+		folio_mark_dirty(folio);
+		folio_unlock(folio);
+		folio_put(folio);
 
-		count -= ret;
-		pos += ret;
-		buf += ret;
+		count -= len;
+		pos += len;
+		buf += len;
 	}
 	memalloc_nofs_restore(pflags);
 
-	return error;
+	if (count)
+		return -ENOMEM;
+	return 0;
 }
 
 /* Find the next written area in the xfile data for a given offset. */