[PATCH] iomap: add a swapfile activation function

["Darrick J. Wong" <darrick.wong@oracle.com>]

From: Darrick J. Wong <darrick.wong@oracle.com>

Add a new iomap_swapfile_activate function so that filesystems can
activate swap files without having to use the obsolete and slow bmap
function.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
 fs/iomap.c            |   99 +++++++++++++++++++++++++++++++++++++++++++++++++
 fs/xfs/xfs_aops.c     |   12 ++++++
 include/linux/iomap.h |    7 +++
 3 files changed, 118 insertions(+)

diff --git a/fs/iomap.c b/fs/iomap.c
index afd1635..ace921b 100644
--- a/fs/iomap.c
+++ b/fs/iomap.c
@@ -1089,3 +1089,102 @@ iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 	return ret;
 }
 EXPORT_SYMBOL_GPL(iomap_dio_rw);
+
+/* Swapfile activation */
+
+struct iomap_swapfile_info {
+	struct swap_info_struct *sis;
+	uint64_t lowest_ppage;		/* lowest physical addr seen (pages) */
+	uint64_t highest_ppage;		/* highest physical addr seen (pages) */
+	unsigned long expected_page_no;	/* next logical offset wanted (pages) */
+	int nr_extents;			/* extent count */
+};
+
+static loff_t iomap_swapfile_activate_actor(struct inode *inode, loff_t pos,
+		loff_t count, void *data, struct iomap *iomap)
+{
+	struct iomap_swapfile_info *isi = data;
+	unsigned long page_no = iomap->offset >> PAGE_SHIFT;
+	unsigned long nr_pages = iomap->length >> PAGE_SHIFT;
+	uint64_t first_ppage = iomap->addr >> PAGE_SHIFT;
+	uint64_t last_ppage = ((iomap->addr + iomap->length) >> PAGE_SHIFT) - 1;
+
+	/* Only one bdev per swap file. */
+	if (iomap->bdev != isi->sis->bdev)
+		goto err;
+
+	/* Must be aligned to a page boundary. */
+	if ((iomap->offset & ~PAGE_MASK) || (iomap->addr & ~PAGE_MASK) ||
+	    (iomap->length & ~PAGE_MASK))
+		goto err;
+
+	/* Only real or unwritten extents. */
+	if (iomap->type != IOMAP_MAPPED && iomap->type != IOMAP_UNWRITTEN)
+		goto err;
+
+	/* No sparse files. */
+	if (isi->expected_page_no != page_no)
+		goto err;
+
+	/* No uncommitted metadata or shared blocks or inline data. */
+	if (iomap->flags & (IOMAP_F_DIRTY | IOMAP_F_SHARED |
+			    IOMAP_F_DATA_INLINE))
+		goto err;
+
+	/*
+	 * Calculate how much swap space we're adding; the first page contains
+	 * the swap header and doesn't count.
+	 */
+	if (page_no == 0)
+		first_ppage++;
+	if (isi->lowest_ppage > first_ppage)
+		isi->lowest_ppage = first_ppage;
+	if (isi->highest_ppage < last_ppage)
+		isi->highest_ppage = last_ppage;
+
+	/* Add extent, set up for the next call. */
+	isi->nr_extents += add_swap_extent(isi->sis, page_no, nr_pages,
+			first_ppage);
+	isi->expected_page_no = page_no + nr_pages;
+
+	return count;
+err:
+	pr_err("swapon: swapfile has holes\n");
+	return -EINVAL;
+}
+
+int iomap_swapfile_activate(struct swap_info_struct *sis,
+		struct file *swap_file, sector_t *pagespan,
+		const struct iomap_ops *ops)
+{
+	struct iomap_swapfile_info isi = {
+		.sis = sis,
+		.lowest_ppage = (sector_t)-1ULL,
+	};
+	struct address_space *mapping = swap_file->f_mapping;
+	struct inode *inode = mapping->host;
+	loff_t pos = 0;
+	loff_t len = i_size_read(inode);
+	loff_t ret;
+
+	ret = filemap_write_and_wait(inode->i_mapping);
+	if (ret)
+		return ret;
+
+	while (len > 0) {
+		ret = iomap_apply(inode, pos, len, IOMAP_REPORT,
+				ops, &isi, iomap_swapfile_activate_actor);
+		if (ret <= 0)
+			return ret;
+
+		pos += ret;
+		len -= ret;
+	}
+
+	*pagespan = 1 + isi.highest_ppage - isi.lowest_ppage;
+	sis->max = isi.expected_page_no;
+	sis->pages = isi.expected_page_no - 1;
+	sis->highest_bit = isi.expected_page_no - 1;
+	return isi.nr_extents;
+}
+EXPORT_SYMBOL_GPL(iomap_swapfile_activate);
diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c
index 0ab824f..80de476 100644
--- a/fs/xfs/xfs_aops.c
+++ b/fs/xfs/xfs_aops.c
@@ -1475,6 +1475,16 @@ xfs_vm_set_page_dirty(
 	return newly_dirty;
 }
 
+static int
+xfs_iomap_swapfile_activate(
+	struct swap_info_struct		*sis,
+	struct file			*swap_file,
+	sector_t			*span)
+{
+	sis->bdev = xfs_find_bdev_for_inode(file_inode(swap_file));
+	return iomap_swapfile_activate(sis, swap_file, span, &xfs_iomap_ops);
+}
+
 const struct address_space_operations xfs_address_space_operations = {
 	.readpage		= xfs_vm_readpage,
 	.readpages		= xfs_vm_readpages,
@@ -1488,6 +1498,7 @@ const struct address_space_operations xfs_address_space_operations = {
 	.migratepage		= buffer_migrate_page,
 	.is_partially_uptodate  = block_is_partially_uptodate,
 	.error_remove_page	= generic_error_remove_page,
+	.swap_activate		= xfs_iomap_swapfile_activate,
 };
 
 const struct address_space_operations xfs_dax_aops = {
@@ -1495,4 +1506,5 @@ const struct address_space_operations xfs_dax_aops = {
 	.direct_IO		= noop_direct_IO,
 	.set_page_dirty		= noop_set_page_dirty,
 	.invalidatepage		= noop_invalidatepage,
+	.swap_activate		= xfs_iomap_swapfile_activate,
 };
diff --git a/include/linux/iomap.h b/include/linux/iomap.h
index 19a07de..66d1c35 100644
--- a/include/linux/iomap.h
+++ b/include/linux/iomap.h
@@ -106,4 +106,11 @@ typedef int (iomap_dio_end_io_t)(struct kiocb *iocb, ssize_t ret,
 ssize_t iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		const struct iomap_ops *ops, iomap_dio_end_io_t end_io);
 
+struct file;
+struct swap_info_struct;
+
+int iomap_swapfile_activate(struct swap_info_struct *sis,
+		struct file *swap_file, sector_t *pagespan,
+		const struct iomap_ops *ops);
+
 #endif /* LINUX_IOMAP_H */