linux-kernel - Re: [PATCH 1/1] debugfs: use IS

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Message-ID: <YTD8+tLP7KeGRXEc@kroah.com>
Date:   Thu, 2 Sep 2021 18:34:02 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Christian König <christian.koenig@....com>
Cc:     Nirmoy Das <nirmoy.das@....com>, rafael@...nel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/1] debugfs: use IS_ERR to check for error

On Thu, Sep 02, 2021 at 05:10:24PM +0200, Christian König wrote:
> Am 02.09.21 um 14:20 schrieb Greg KH:
> > On Thu, Sep 02, 2021 at 02:03:12PM +0200, Christian König wrote:
> > > 
> > > Am 02.09.21 um 12:38 schrieb Greg KH:
> > > > On Thu, Sep 02, 2021 at 12:29:17PM +0200, Nirmoy Das wrote:
> > > > > debugfs_create_file() returns encoded error so
> > > > > use IS_ERR for checking return value.
> > > > > 
> > > > > References: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.freedesktop.org%2Fdrm%2Famd%2F-%2Fissues%2F1686&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7Cffc1109aeb744082181b08d96e0c06db%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637661820207117289%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=6NDHX9sEhGF2jakVfUJ7Qurql6UAdNpFQZ6XvCjwz0E%3D&amp;reserved=0
> > > > > Signed-off-by: Nirmoy Das <nirmoy.das@....com>
> > > > > ---
> > > > >    fs/debugfs/inode.c | 2 +-
> > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > 
> > > > > diff --git a/fs/debugfs/inode.c b/fs/debugfs/inode.c
> > > > > index 8129a430d789..2f117c57160d 100644
> > > > > --- a/fs/debugfs/inode.c
> > > > > +++ b/fs/debugfs/inode.c
> > > > > @@ -528,7 +528,7 @@ void debugfs_create_file_size(const char *name, umode_t mode,
> > > > >    {
> > > > >    	struct dentry *de = debugfs_create_file(name, mode, parent, data, fops);
> > > > > -	if (de)
> > > > > +	if (!IS_ERR(de))
> > > > >    		d_inode(de)->i_size = file_size;
> > > > >    }
> > > > >    EXPORT_SYMBOL_GPL(debugfs_create_file_size);
> > > > > -- 
> > > > > 2.32.0
> > > > > 
> > > > Ah, good catch, I'll queue this up after 5.15-rc1 is out, thanks!
> > > Thinking more about this if I'm not completely mistaken
> > > debugfs_create_file() returns -ENODEV when debugfs is disabled and NULL on
> > > any other error.
> > How can this function be called if debugfs is not enabled in the system
> > configuration?  This _is_ the debugfs core code.
> 
> Well, that's what I meant. The original code is correct and Nirmoy's patch
> here is breaking it.

Ah, yes, sorry, you are right.  This function can not return an error
value, if something went wrong, the result will always be NULL.

> Nirmoys other patch is for a driver and there the function can indeed return
> both error code and NULL.

You should never be checking this stuff in a caller anyway, so no, don't
do it there either.

thanks,

greg k-h