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Date:   Tue, 10 Oct 2023 10:51:32 +0300
From:   Dan Carpenter <dan.carpenter@linaro.org>
To:     Su Hui <suhui@nfschina.com>
Cc:     ericvh@kernel.org, lucho@ionkov.net, asmadeus@codewreck.org,
        linux_oss@crudebyte.com, v9fs@lists.linux.dev,
        linux-kernel@vger.kernel.org, kernel-janitors@vger.kernel.org
Subject: Re: [PATCH] fs/9p/xattr.c: avoid format-overflow warning
Message-ID: <56aa4f09-8f61-48f3-9836-687bf852b03a@kadam.mountain>
References: <20231008060138.517057-1-suhui@nfschina.com>
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On Sun, Oct 08, 2023 at 02:01:39PM +0800, Su Hui wrote:
> with gcc and W=1 option, there's a warning like this:
> 
> In file included from fs/9p/xattr.c:12:
> In function ‘v9fs_xattr_get’,
>     inlined from ‘v9fs_listxattr’ at fs/9p/xattr.c:142:9:
> include/net/9p/9p.h:55:2: error: ‘%s’ directive argument is null
> [-Werror=format-overflow=]
>    55 |  _p9_debug(level, __func__, fmt, ##__VA_ARGS__)
>       |  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> use "" replace NULL to silence this warning.
> 
> Signed-off-by: Su Hui <suhui@nfschina.com>
> ---
>  fs/9p/xattr.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/fs/9p/xattr.c b/fs/9p/xattr.c
> index e00cf8109b3f..d995ee080835 100644
> --- a/fs/9p/xattr.c
> +++ b/fs/9p/xattr.c
> @@ -139,7 +139,7 @@ int v9fs_fid_xattr_set(struct p9_fid *fid, const char *name,
>  
>  ssize_t v9fs_listxattr(struct dentry *dentry, char *buffer, size_t buffer_size)
>  {
> -	return v9fs_xattr_get(dentry, NULL, buffer, buffer_size);
> +	return v9fs_xattr_get(dentry, "", buffer, buffer_size);

I'm pretty uncomfortable with this patch...  This code is 13 years old
so it can't be too huge of a problem.  We're doing this for the printks,
but now they're going to look weird first of all.

Old: "file = (null)"
New: "file = "

But also this must have some other effects on runtime right?

regards,
dan carpenter