linux-kernel - Re: [PATCH] initrd: Fix unused variable warning in rd_load

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Message-ID: <20250910095237.9573B41-hca@linux.ibm.com>
Date: Wed, 10 Sep 2025 11:52:37 +0200
From: Heiko Carstens <hca@...ux.ibm.com>
To: Thorsten Blum <thorsten.blum@...ux.dev>
Cc: Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
        linux-s390@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] initrd: Fix unused variable warning in rd_load_image()
 on s390

On Mon, Sep 08, 2025 at 02:13:04PM +0200, Thorsten Blum wrote:
> The local variable 'rotate' is not used on s390, and building the kernel
> with W=1 generates the following warning:
> 
> init/do_mounts_rd.c:192:17: warning: variable 'rotate' set but not used [-Wunused-but-set-variable]
>   192 |         unsigned short rotate = 0;
>       |                        ^
> 1 warning generated.
> 
> Fix this by declaring and using 'rotate' only when CONFIG_S390 is not
> defined.
> 
> Signed-off-by: Thorsten Blum <thorsten.blum@...ux.dev>
> ---
>  init/do_mounts_rd.c | 4 +++-
>  1 file changed, 3 insertions(+), 1 deletion(-)
> 
> diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
> index ac021ae6e6fa..cbc4c496cb5f 100644
> --- a/init/do_mounts_rd.c
> +++ b/init/do_mounts_rd.c
> @@ -189,9 +189,9 @@ int __init rd_load_image(char *from)
>  	unsigned long rd_blocks, devblocks;
>  	int nblocks, i;
>  	char *buf = NULL;
> -	unsigned short rotate = 0;
>  	decompress_fn decompressor = NULL;
>  #if !defined(CONFIG_S390)
> +	unsigned short rotate = 0;
>  	char rotator[4] = { '|' , '/' , '-' , '\\' };
>  #endif
>  
> @@ -249,7 +249,9 @@ int __init rd_load_image(char *from)
>  	for (i = 0; i < nblocks; i++) {
>  		if (i && (i % devblocks == 0)) {
>  			pr_cont("done disk #1.\n");
> +#if !defined(CONFIG_S390)
>  			rotate = 0;
> +#endif

Instead of adding even more ifdefs, wouldn't it make more sense to get
rid of them and leave it up to the compiler to optimize unused stuff
away? Something like this instead:

diff --git a/init/do_mounts_rd.c b/init/do_mounts_rd.c
index ac021ae6e6fa..0cc9caf2411d 100644
--- a/init/do_mounts_rd.c
+++ b/init/do_mounts_rd.c
@@ -191,9 +191,7 @@ int __init rd_load_image(char *from)
 	char *buf = NULL;
 	unsigned short rotate = 0;
 	decompress_fn decompressor = NULL;
-#if !defined(CONFIG_S390)
 	char rotator[4] = { '|' , '/' , '-' , '\\' };
-#endif
 
 	out_file = filp_open("/dev/ram", O_RDWR, 0);
 	if (IS_ERR(out_file))
@@ -255,12 +253,11 @@ int __init rd_load_image(char *from)
 		}
 		kernel_read(in_file, buf, BLOCK_SIZE, &in_pos);
 		kernel_write(out_file, buf, BLOCK_SIZE, &out_pos);
-#if !defined(CONFIG_S390)
 		if (!(i % 16)) {
-			pr_cont("%c\b", rotator[rotate & 0x3]);
+			if (!IS_ENABLED(CONFIG_S390))
+				pr_cont("%c\b", rotator[rotate & 0x3]);
 			rotate++;
 		}
-#endif
 	}
 	pr_cont("done.\n");