fs: add CONFIG_BUFFER_HEAD

Add a new config option that controls building the buffer_head code, and
select it from all file systems and stacking drivers that need it.

For the block device nodes and alternative iomap based buffered I/O path
is provided when buffer_head support is not enabled, and iomap needs a
a small tweak to define the IOMAP_F_BUFFER_HEAD flag to 0 to not call
into the buffer_head code when it doesn't exist.

Otherwise this is just Kconfig and ifdef changes.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Luis Chamberlain <mcgrof@kernel.org>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Link: https://lore.kernel.org/r/20230801172201.1923299-7-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 60 insertions, 10 deletions

diff --git a/block/fops.c b/block/fops.c
index 063ece37d44e..eaa98a987213 100644
--- a/block/fops.c
+++ b/block/fops.c
@@ -24,15 +24,6 @@ static inline struct inode *bdev_file_inode(struct file *file)
 	return file->f_mapping->host;
 }
 
-static int blkdev_get_block(struct inode *inode, sector_t iblock,
-		struct buffer_head *bh, int create)
-{
-	bh->b_bdev = I_BDEV(inode);
-	bh->b_blocknr = iblock;
-	set_buffer_mapped(bh);
-	return 0;
-}
-
 static blk_opf_t dio_bio_write_op(struct kiocb *iocb)
 {
 	blk_opf_t opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
@@ -400,7 +391,7 @@ static int blkdev_iomap_begin(struct inode *inode, loff_t offset, loff_t length,
 	iomap->type = IOMAP_MAPPED;
 	iomap->addr = iomap->offset;
 	iomap->length = isize - iomap->offset;
-	iomap->flags |= IOMAP_F_BUFFER_HEAD;
+	iomap->flags |= IOMAP_F_BUFFER_HEAD; /* noop for !CONFIG_BUFFER_HEAD */
 	return 0;
 }
 
@@ -408,6 +399,16 @@ static const struct iomap_ops blkdev_iomap_ops = {
 	.iomap_begin		= blkdev_iomap_begin,
 };
 
+#ifdef CONFIG_BUFFER_HEAD
+static int blkdev_get_block(struct inode *inode, sector_t iblock,
+		struct buffer_head *bh, int create)
+{
+	bh->b_bdev = I_BDEV(inode);
+	bh->b_blocknr = iblock;
+	set_buffer_mapped(bh);
+	return 0;
+}
+
 static int blkdev_writepage(struct page *page, struct writeback_control *wbc)
 {
 	return block_write_full_page(page, blkdev_get_block, wbc);
@@ -453,6 +454,55 @@ const struct address_space_operations def_blk_aops = {
 	.migrate_folio	= buffer_migrate_folio_norefs,
 	.is_dirty_writeback = buffer_check_dirty_writeback,
 };
+#else /* CONFIG_BUFFER_HEAD */
+static int blkdev_read_folio(struct file *file, struct folio *folio)
+{
+	return iomap_read_folio(folio, &blkdev_iomap_ops);
+}
+
+static void blkdev_readahead(struct readahead_control *rac)
+{
+	iomap_readahead(rac, &blkdev_iomap_ops);
+}
+
+static int blkdev_map_blocks(struct iomap_writepage_ctx *wpc,
+		struct inode *inode, loff_t offset)
+{
+	loff_t isize = i_size_read(inode);
+
+	if (WARN_ON_ONCE(offset >= isize))
+		return -EIO;
+	if (offset >= wpc->iomap.offset &&
+	    offset < wpc->iomap.offset + wpc->iomap.length)
+		return 0;
+	return blkdev_iomap_begin(inode, offset, isize - offset,
+				  IOMAP_WRITE, &wpc->iomap, NULL);
+}
+
+static const struct iomap_writeback_ops blkdev_writeback_ops = {
+	.map_blocks		= blkdev_map_blocks,
+};
+
+static int blkdev_writepages(struct address_space *mapping,
+		struct writeback_control *wbc)
+{
+	struct iomap_writepage_ctx wpc = { };
+
+	return iomap_writepages(mapping, wbc, &wpc, &blkdev_writeback_ops);
+}
+
+const struct address_space_operations def_blk_aops = {
+	.dirty_folio	= filemap_dirty_folio,
+	.release_folio		= iomap_release_folio,
+	.invalidate_folio	= iomap_invalidate_folio,
+	.read_folio		= blkdev_read_folio,
+	.readahead		= blkdev_readahead,
+	.writepages		= blkdev_writepages,
+	.is_partially_uptodate  = iomap_is_partially_uptodate,
+	.error_remove_page	= generic_error_remove_page,
+	.migrate_folio		= filemap_migrate_folio,
+};
+#endif /* CONFIG_BUFFER_HEAD */
 
 /*
  * for a block special file file_inode(file)->i_size is zero