xfs: remove dax code from object file when disabled

We check IS_DAX(inode) before calling either xfs_file_dax_read or
xfs_file_dax_write, and this will lead the call being optimized out at
compile time when CONFIG_FS_DAX is disabled.

However, the two functions are marked STATIC, so they become global
symbols when CONFIG_XFS_DEBUG is set, leaving us with two unused global
functions that call into an undefined function and a broken "allmodconfig"
build:

fs/built-in.o: In function `xfs_file_dax_read':
fs/xfs/xfs_file.c:348: undefined reference to `dax_do_io'
fs/built-in.o: In function `xfs_file_dax_write':
fs/xfs/xfs_file.c:758: undefined reference to `dax_do_io'

Marking the two functions 'static noinline' instead of 'STATIC' will let
the compiler drop the symbols when there are no callers but avoid the
implicit inlining.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: 16d4d435 ("xfs: split direct I/O and DAX path")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_file.c

@@ -370,7 +370,7 @@ xfs_file_dio_aio_read(
 	return ret;
 }
 
-STATIC ssize_t
+static noinline ssize_t
 xfs_file_dax_read(
 	struct kiocb		*iocb,
 	struct iov_iter		*to)
@@ -875,7 +875,7 @@ xfs_file_dio_aio_write(
 	return ret;
 }
 
-STATIC ssize_t
+static noinline ssize_t
 xfs_file_dax_write(
 	struct kiocb		*iocb,
 	struct iov_iter		*from)