linux-kernel - Re: [RFC PATCH v1 07/12] efi: Replace strstarts() by str_has

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Message-ID: <ab769a5188394cd3379cc627d14a0222050a1367.camel@HansenPartnership.com>
Date:   Fri, 04 Dec 2020 10:02:09 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Ard Biesheuvel <ardb@...nel.org>,
        laniel_francis@...vacyrequired.com
Cc:     linux-efi <linux-efi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v1 07/12] efi: Replace strstarts() by
 str_has_prefix().

On Fri, 2020-12-04 at 18:07 +0100, Ard Biesheuvel wrote:
> On Fri, 4 Dec 2020 at 18:06, <laniel_francis@...vacyrequired.com>
> wrote:
> > From: Francis Laniel <laniel_francis@...vacyrequired.com>
> > 
> > The two functions indicates if a string begins with a given prefix.
> > The only difference is that strstarts() returns a bool while
> > str_has_prefix()
> > returns the length of the prefix if the string begins with it or 0
> > otherwise.
> > 
> 
> Why? 

I think I can answer that.  If the conversion were done properly (which
it's not) you could get rid of the double strings in the code which are
error prone if you update one and forget another.  This gives a good
example: 3d739c1f6156 ("tracing: Use the return of str_has_prefix() to
remove open coded numbers"). so in your code you'd replace things like

    if (strstarts(option, "rgb")) {
        option += strlen("rgb");
        ...

with 

    len = str_has_prefix(option, "rgb");
    if (len) {
        option += len
        ...

Obviously you also have cases where strstart is used as a boolean with
no need to know the length ... I think there's no value to converting
those.

James