xfs: use bios directly to read and write the log recovery buffers

The xfs_buf structure is basically used as a glorified container for
a memory allocation in the log recovery code.  Replace it with a
call to kmem_alloc_large and a simple abstraction to read into or
write from it synchronously using chained bios.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/Makefile

@@ -62,6 +62,7 @@ xfs-y				+= xfs_aops.o \
 				   xfs_attr_inactive.o \
 				   xfs_attr_list.o \
 				   xfs_bmap_util.o \
+				   xfs_bio_io.o \
 				   xfs_buf.o \
 				   xfs_dir2_readdir.o \
 				   xfs_discard.o \

fs/xfs/xfs_bio_io.c

+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (c) 2019 Christoph Hellwig.
+ */
+#include "xfs.h"
+
+static inline unsigned int bio_max_vecs(unsigned int count)
+{
+	return min_t(unsigned, howmany(count, PAGE_SIZE), BIO_MAX_PAGES);
+}
+
+int
+xfs_rw_bdev(
+	struct block_device	*bdev,
+	sector_t		sector,
+	unsigned int		count,
+	char			*data,
+	unsigned int		op)
+
+{
+	unsigned int		is_vmalloc = is_vmalloc_addr(data);
+	unsigned int		left = count;
+	int			error;
+	struct bio		*bio;
+
+	if (is_vmalloc && op == REQ_OP_WRITE)
+		flush_kernel_vmap_range(data, count);
+
+	bio = bio_alloc(GFP_KERNEL, bio_max_vecs(left));
+	bio_set_dev(bio, bdev);
+	bio->bi_iter.bi_sector = sector;
+	bio->bi_opf = op | REQ_META | REQ_SYNC;
+
+	do {
+		struct page	*page = kmem_to_page(data);
+		unsigned int	off = offset_in_page(data);
+		unsigned int	len = min_t(unsigned, left, PAGE_SIZE - off);
+
+		while (bio_add_page(bio, page, len, off) != len) {
+			struct bio	*prev = bio;
+
+			bio = bio_alloc(GFP_KERNEL, bio_max_vecs(left));
+			bio_copy_dev(bio, prev);
+			bio->bi_iter.bi_sector = bio_end_sector(prev);
+			bio->bi_opf = prev->bi_opf;
+			bio_chain(bio, prev);
+
+			submit_bio(prev);
+		}
+
+		data += len;
+		left -= len;
+	} while (left > 0);
+
+	error = submit_bio_wait(bio);
+	bio_put(bio);
+
+	if (is_vmalloc && op == REQ_OP_READ)
+		invalidate_kernel_vmap_range(data, count);
+	return error;
+}

fs/xfs/xfs_linux.h

@@ -219,6 +219,9 @@ static inline uint64_t howmany_64(uint64_t x, uint32_t y)
 	return x;
 }
 
+int xfs_rw_bdev(struct block_device *bdev, sector_t sector, unsigned int count,
+		char *data, unsigned int op);
+
 #define ASSERT_ALWAYS(expr)	\
 	(likely(expr) ? (void)0 : assfail(#expr, __FILE__, __LINE__))