linux-kernel - Re: [PATCH 1/2] vfs: parse: deal with zero length string value

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Date:   Fri, 1 Jul 2022 14:29:23 +0800
From:   Ian Kent <raven@...maw.net>
To:     Al Viro <viro@...iv.linux.org.uk>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Siddhesh Poyarekar <siddhesh@...plt.org>,
        David Howells <dhowells@...hat.com>,
        Miklos Szeredi <miklos@...redi.hu>,
        Carlos Maiolino <cmaiolino@...hat.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] vfs: parse: deal with zero length string value


On 29/6/22 09:06, Ian Kent wrote:
>
> On 29/6/22 01:55, Al Viro wrote:
>> On Tue, Jun 28, 2022 at 08:30:52AM +0800, Ian Kent wrote:
>>> Parsing an fs string that has zero length should result in the 
>>> parameter
>>> being set to NULL so that downstream processing handles it correctly.
>>> For example, the proc mount table processing should print "(none)" in
>>> this case to preserve mount record field count, but if the value points
>>> to the NULL string this doesn't happen.
>>     Hmmm...  And what happens if you feed that to ->parse_param(), which
>> calls fs_parse(), which decides that param->key looks like a name of 
>> e.g.
>> u32 option and calls fs_param_is_u32() to see what's what?  OOPS is a 
>> form
>> of rejection, I suppose, but...
>
> Oh ... yes, would you be ok with an update that moves the
>
> "param.type = fs_value_is_string;" inside the above else
>
> clause?

Looks like I'll need to use a type other than fs_value_is_string

so I can identify the case in those conversion functions when

there's no value for the parameter.


I'm tempted to use fs_value_is_flag since it's already present but

a new type of fs_value_is_empty is probably better.


What do you think about doing it like this and that type naming too?


Ian