linux-kernel - [PATCH] procfs: use inline functions instead of macros for proc_create_single

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Date:   Fri, 25 May 2018 23:45:00 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Arnd Bergmann <arnd@...db.de>, Christoph Hellwig <hch@....de>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Richard Weinberger <richard@....at>,
        Miquel Raynal <miquel.raynal@...tlin.com>,
        Rafał Miłecki <rafal@...ecki.pl>,
        linux-mtd@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: [PATCH] procfs: use inline functions instead of macros for proc_create_single_data stub

The procfs interface changes caused one warning in afs for
a now unused function:

fs/afs/proc.c:818:12: error: 'afs_proc_stats_show' defined but not used [-Werror=unused-function]
 static int afs_proc_stats_show(struct seq_file *m, void *v)

This can be avoided by using an inline function instead of a macro
to reference it, so now the compiler can silently drop the function
after seeing that there is a reference but that it is never called.

Unfortunately, this change triggers another warning where a function
is hidden and now unexpectedly referenced:

drivers/mtd/mtdcore.c: In function 'init_mtd':
drivers/mtd/mtdcore.c:1878:48: error: 'mtd_proc_show' undeclared (first use in this function); did you mean 'mtd_name_show'?

It seems nicer to keep using the inline function and removing the #ifdef
here than to add an #ifdef around every single function we pass into
proc_create_single_data(), so I'm removing the #ifdef here.

After a few hundred randconfig builds, this was the only instance
I found that caused a problem.

Fixes: 353861cf0594 ("afs: simplify procfs code")
Fixes: 3f3942aca6da ("proc: introduce proc_create_single{,_data}")
Cc: Christoph Hellwig <hch@....de>
Signed-off-by: Arnd Bergmann <arnd@...db.de>
---
 drivers/mtd/mtdcore.c   |  3 ---
 include/linux/proc_fs.h | 10 ++++++++--
 2 files changed, 8 insertions(+), 5 deletions(-)

diff --git a/drivers/mtd/mtdcore.c b/drivers/mtd/mtdcore.c
index 42395df06be9..08d1e89faf9c 100644
--- a/drivers/mtd/mtdcore.c
+++ b/drivers/mtd/mtdcore.c
@@ -1814,8 +1814,6 @@ void *mtd_kmalloc_up_to(const struct mtd_info *mtd, size_t *size)
 }
 EXPORT_SYMBOL_GPL(mtd_kmalloc_up_to);
 
-#ifdef CONFIG_PROC_FS
-
 /*====================================================================*/
 /* Support for /proc/mtd */
 
@@ -1833,7 +1831,6 @@ static int mtd_proc_show(struct seq_file *m, void *v)
 	mutex_unlock(&mtd_table_mutex);
 	return 0;
 }
-#endif /* CONFIG_PROC_FS */
 
 /*====================================================================*/
 /* Init code */
diff --git a/include/linux/proc_fs.h b/include/linux/proc_fs.h
index e518352137e7..3b44c357a6e7 100644
--- a/include/linux/proc_fs.h
+++ b/include/linux/proc_fs.h
@@ -84,8 +84,14 @@ static inline struct proc_dir_entry *proc_mkdir_mode(const char *name,
 #define proc_create_seq_private(name, mode, parent, ops, size, data) ({NULL;})
 #define proc_create_seq_data(name, mode, parent, ops, data) ({NULL;})
 #define proc_create_seq(name, mode, parent, ops) ({NULL;})
-#define proc_create_single(name, mode, parent, show) ({NULL;})
-#define proc_create_single_data(name, mode, parent, show, data) ({NULL;})
+static inline struct proc_dir_entry *proc_create_single_data(const char *name,
+		umode_t mode, struct proc_dir_entry *parent,
+		int (*show)(struct seq_file *, void *), void *data)
+{
+	return NULL;
+}
+#define proc_create_single(name, mode, parent, show) \
+	proc_create_single_data(name, mode, parent, show, NULL)
 #define proc_create(name, mode, parent, proc_fops) ({NULL;})
 #define proc_create_data(name, mode, parent, proc_fops, data) ({NULL;})
 
-- 
2.9.0