linux-kernel - [PATCH] xfs: remove dax code from object file when disabled

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Message-Id: <20160721120824.2797655-1-arnd@arndb.de>
Date:	Thu, 21 Jul 2016 14:07:50 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Dave Chinner <david@...morbit.com>, xfs@....sgi.com
Cc:	Christoph Hellwig <hch@....de>, Arnd Bergmann <arnd@...db.de>,
	Brian Foster <bfoster@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Ross Zwisler <ross.zwisler@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Eric Sandeen <sandeen@...hat.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	linux-kernel@...r.kernel.org
Subject: [PATCH] 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@...db.de>
Fixes: 16d4d43595b4 ("xfs: split direct I/O and DAX path")
---
 fs/xfs/xfs_file.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 8ffacb8bba19..ed95e5bb04e6 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -327,7 +327,7 @@ 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)
@@ -706,7 +706,7 @@ out:
 	return ret;
 }
 
-STATIC ssize_t
+static noinline ssize_t
 xfs_file_dax_write(
 	struct kiocb		*iocb,
 	struct iov_iter		*from)
-- 
2.9.0