linux-kernel - Re: [PATCH] fs/9p/xattr.c: avoid format-overflow warning

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Message-ID: <13910281.Zj71IQSfG8@silver>
Date:   Mon, 09 Oct 2023 20:34:15 +0200
From:   Christian Schoenebeck <linux_oss@...debyte.com>
To:     ericvh@...nel.org, lucho@...kov.net, asmadeus@...ewreck.org,
        Su Hui <suhui@...china.com>, v9fs@...ts.linux.dev
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] fs/9p/xattr.c: avoid format-overflow warning

On Sunday, October 8, 2023 8:01:39 AM CEST 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@...china.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);
>  }
>  
>  static int v9fs_xattr_handler_get(const struct xattr_handler *handler,
> 

Mmm, that's not the same is it? Have you tested this change?

Currently this function causes a 'Txattrwalk' 9p message to be sent to 9p
server with its name[s] field being NULL, and the latter being the magical
hint to 9p server to not send an attribute, but rather the list of attributes.

With your change I would assume that it would rather ask server for one
attribute called "". I have not tested myself, just worrying that it might
break behaviour.

/Christian