Re: [PATCH 1/1] debugfs: use IS_ERR to check for error

[Christian König]

Am 02.09.21 um 19:01 schrieb Das, Nirmoy:
> On 9/2/2021 6:34 PM, Greg KH wrote:
> > 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&data=04%7C01%7Cnirmoy.das%40amd.com%7C7a1f1095c0d64416576c08d96e2f7b38%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637661973378236086%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&sdata=g9BQRJG8gvjGFq6oj5vk9PCemQ39U19CLmkMNHVUafg%3D&reserved=0
> > > > > > > Signed-off-by: Nirmoy Das <nirmoy.das@xxxxxxx>
> > > > > > > ---
> > > > > > >     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.
>
>
> I just realized that we don't return NULL on error anymore:
>
> commit ff9fb72bc07705c00795ca48631f7fffe24d2c6b
> Author: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> Date:   Wed Jan 23 11:28:14 2019 +0100
>
>     debugfs: return error values, not NULL
>
>
> and the current doc also says "If an error occurs, ERR_PTR(-ERROR) 
> will be returned."
>
> If I am not missing anything, this patch should be fine.

Ah! Yes, now that makes sense.

Looks like that my memory and the documentation under 
https://www.kernel.org/doc/htmldocs/filesystems/API-debugfs-create-file.html 
is outdated.

I can update my memory, but I have no idea where this documentation 
comes from and how to fix it.

Regards,
Christian.

> Regards,
>
> Nirmoy
>
> > > 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