fs: build the legacy direct I/O code conditionally

Add a new LEGACY_DIRECT_IO config symbol that is only selected by the
file systems that still use the legacy blockdev_direct_IO code, so that
kernels without support for those file systems don't need to build the
code.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20230125065839.191256-3-hch@lst.de
Signed-off-by: Jens Axboe <axboe@kernel.dk>

fs/Kconfig

@@ -18,6 +18,10 @@ config VALIDATE_FS_PARSER
 config FS_IOMAP
 	bool
 
+# old blockdev_direct_IO implementation.  Use iomap for new code instead
+config LEGACY_DIRECT_IO
+	bool
+
 if BLOCK
 
 source "fs/ext2/Kconfig"

fs/Makefile

@@ -19,13 +19,14 @@ obj-y :=	open.o read_write.o file_table.o super.o \
 		kernel_read_file.o remap_range.o
 
 ifeq ($(CONFIG_BLOCK),y)
-obj-y +=	buffer.o direct-io.o mpage.o
+obj-y +=	buffer.o mpage.o
 else
 obj-y +=	no-block.o
 endif
 
 obj-$(CONFIG_PROC_FS) += proc_namespace.o
 
+obj-$(CONFIG_LEGACY_DIRECT_IO)	+= direct-io.o
 obj-y				+= notify/
 obj-$(CONFIG_EPOLL)		+= eventpoll.o
 obj-y				+= anon_inodes.o

fs/affs/Kconfig

@@ -2,6 +2,7 @@
 config AFFS_FS
 	tristate "Amiga FFS file system support"
 	depends on BLOCK
+	select LEGACY_DIRECT_IO
 	help
 	  The Fast File System (FFS) is the common file system used on hard
 	  disks by Amiga(tm) systems since AmigaOS Version 1.3 (34.20).  Say Y

fs/exfat/Kconfig

@@ -3,6 +3,7 @@
 config EXFAT_FS
 	tristate "exFAT filesystem support"
 	select NLS
+	select LEGACY_DIRECT_IO
 	help
 	  This allows you to mount devices formatted with the exFAT file system.
 	  exFAT is typically used on SD-Cards or USB sticks.

fs/ext2/Kconfig

@@ -2,6 +2,7 @@
 config EXT2_FS
 	tristate "Second extended fs support"
 	select FS_IOMAP
+	select LEGACY_DIRECT_IO
 	help
 	  Ext2 is a standard Linux file system for hard disks.
 

fs/fat/Kconfig

@@ -2,6 +2,7 @@
 config FAT_FS
 	tristate
 	select NLS
+	select LEGACY_DIRECT_IO
 	help
 	  If you want to use one of the FAT-based file systems (the MS-DOS and
 	  VFAT (Windows 95) file systems), then you must say Y or M here

fs/hfs/Kconfig

@@ -3,6 +3,7 @@ config HFS_FS
 	tristate "Apple Macintosh file system support"
 	depends on BLOCK
 	select NLS
+	select LEGACY_DIRECT_IO
 	help
 	  If you say Y here, you will be able to mount Macintosh-formatted
 	  floppy disks and hard drive partitions with full read-write access.

fs/hfsplus/Kconfig

@@ -4,6 +4,7 @@ config HFSPLUS_FS
 	depends on BLOCK
 	select NLS
 	select NLS_UTF8
+	select LEGACY_DIRECT_IO
 	help
 	  If you say Y here, you will be able to mount extended format
 	  Macintosh-formatted hard drive partitions with full read-write access.

fs/jfs/Kconfig

@@ -3,6 +3,7 @@ config JFS_FS
 	tristate "JFS filesystem support"
 	select NLS
 	select CRC32
+	select LEGACY_DIRECT_IO
 	help
 	  This is a port of IBM's Journaled Filesystem .  More information is
 	  available in the file <file:Documentation/admin-guide/jfs.rst>.

fs/nilfs2/Kconfig

@@ -2,6 +2,7 @@
 config NILFS2_FS
 	tristate "NILFS2 file system support"
 	select CRC32
+	select LEGACY_DIRECT_IO
 	help
 	  NILFS2 is a log-structured file system (LFS) supporting continuous
 	  snapshotting.  In addition to versioning capability of the entire

fs/ntfs3/Kconfig

@@ -2,6 +2,7 @@
 config NTFS3_FS
 	tristate "NTFS Read-Write file system support"
 	select NLS
+	select LEGACY_DIRECT_IO
 	help
 	  Windows OS native file system (NTFS) support up to NTFS version 3.1.
 

fs/ocfs2/Kconfig

@@ -7,6 +7,7 @@ config OCFS2_FS
 	select QUOTA
 	select QUOTA_TREE
 	select FS_POSIX_ACL
+	select LEGACY_DIRECT_IO
 	help
 	  OCFS2 is a general purpose extent based shared disk cluster file
 	  system with many similarities to ext3. It supports 64 bit inode

fs/reiserfs/Kconfig

@@ -2,6 +2,7 @@
 config REISERFS_FS
 	tristate "Reiserfs support (deprecated)"
 	select CRC32
+	select LEGACY_DIRECT_IO
 	help
 	  Reiserfs is deprecated and scheduled to be removed from the kernel
 	  in 2025. If you are still using it, please migrate to another

fs/udf/Kconfig

@@ -3,6 +3,7 @@ config UDF_FS
 	tristate "UDF file system support"
 	select CRC_ITU_T
 	select NLS
+	select LEGACY_DIRECT_IO
 	help
 	  This is a file system used on some CD-ROMs and DVDs. Since the
 	  file system is supported by multiple operating systems and is more