linux-kernel - Re: [PATCH v2] fbdev: Use helper to get fb

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Message-ID: <3f8f697f-7b85-cb8c-445a-8d7c40a062f8@redhat.com>
Date:   Wed, 4 May 2022 10:26:30 +0200
From:   Javier Martinez Canillas <javierm@...hat.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>,
        linux-kernel@...r.kernel.org
Cc:     Sam Ravnborg <sam@...nborg.org>, Maxime Ripard <maxime@...no.tech>,
        Junxiao Chang <junxiao.chang@...el.com>,
        dri-devel@...ts.freedesktop.org, linux-fbdev@...r.kernel.org
Subject: Re: [PATCH v2] fbdev: Use helper to get fb_info in all file
 operations

Hello Thomas,

On 5/4/22 10:15, Thomas Zimmermann wrote:
> Hi
> 
> Am 03.05.22 um 22:19 schrieb Javier Martinez Canillas:
>> A reference to the framebuffer device struct fb_info is stored in the file
>> private data, but this reference could no longer be valid and must not be
>> accessed directly. Instead, the file_fb_info() accessor function must be
>> used since it does sanity checking to make sure that the fb_info is valid.
>>
>> This can happen for example if the registered framebuffer device is for a
>> driver that just uses a framebuffer provided by the system firmware. In
>> that case, the fbdev core would unregister the framebuffer device when a
>> real video driver is probed and ask to remove conflicting framebuffers.
>>
>> Most fbdev file operations already use the helper to get the fb_info but
>> get_fb_unmapped_area() and fb_deferred_io_fsync() don't. Fix those two.
>>
>> Since fb_deferred_io_fsync() is not in fbmem.o, the helper has to be
>> exported. Rename it and add a fb_ prefix to denote that is public now.
>>
>> Reported-by: Junxiao Chang <junxiao.chang@...el.com>
>> Signed-off-by: Javier Martinez Canillas <javierm@...hat.com>
> 
> Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>
>

Thanks.
 
> Please see my comment below.

[snip]

>>   
>> +	if (!info)
>> +		return -ENODEV;
>> +
> 
> This is consistent with other functions, but it's probably not the 
> correct errno code. It means that a device is not available for opening.
> 
> But the situation here is rather as with close() on a 
> disconnected-network file. The call to close() returns EIO in this case. 
> Maybe we should consider changing this in a separate patch.
>

Indeed. Agree that -EIO makes more sense here.
 
> Best regards
> Thomas
> 
-- 
Best regards,

Javier Martinez Canillas
Linux Engineering
Red Hat