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

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

[Su Hui]

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);
 }
 
 static int v9fs_xattr_handler_get(const struct xattr_handler *handler,
-- 
2.30.2

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

[Christian Schoenebeck]

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@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);
>  }
>  
>  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

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

[Su Hui]

On 2023/10/10 02:34, Christian Schoenebeck wrote:
> 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@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);
>>   }
>>   
>>   static int v9fs_xattr_handler_get(const struct xattr_handler *handler,
>>
> Mmm, that's not the same is it? Have you tested this change?
Oh, sorry.  That's not the same and I just tested compilation.
>
> 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.
Got it, I made a mistake there. Thanks for your explanation.
Sorry for the noise again.

Su Hui

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

[asmadeus]

Christian Schoenebeck wrote on Mon, Oct 09, 2023 at 08:34:15PM +0200:
> > +++ 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.

p9pdu_vwritef should output the same (just a 0 length) for both NULL and
"" so I think it should be ok, but it definitely needs testing.

I'll try to find time to check (getfattr -d should be enough) later this
week and add it to the pile

-- 
Dominique Martinet | Asmadeus

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

[Christian Schoenebeck]

On Tuesday, October 10, 2023 4:23:06 AM CEST asmadeus@codewreck.org wrote:
> Christian Schoenebeck wrote on Mon, Oct 09, 2023 at 08:34:15PM +0200:
> > > +++ 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.
> 
> p9pdu_vwritef should output the same (just a 0 length) for both NULL and
> "" so I think it should be ok, but it definitely needs testing.
> 
> I'll try to find time to check (getfattr -d should be enough) later this
> week and add it to the pile

Yeah, I think you are right Dominique, it should end up the same as both cases
result in a string length of 0.

/Christian

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

[Dan Carpenter]

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

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

[Su Hui]

On 2023/10/10 15:51, Dan Carpenter wrote:
> 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 = "
Agreed, this looks  really weird and the patch is just for avoiding 
gcc's warning.
Sorry for the noise.

Su Hui

>
> But also this must have some other effects on runtime right?
>
> regards,
> dan carpenter
>