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From:   Francis Laniel <laniel_francis@privacyrequired.com>
To:     James Bottomley <James.Bottomley@hansenpartnership.com>
Cc:     Ard Biesheuvel <ardb@kernel.org>,
        linux-efi <linux-efi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
Subject: Re: [RFC PATCH v1 07/12] efi: Replace strstarts() by str_has_prefix().
Date:   Sat, 05 Dec 2020 20:08:53 +0100
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Le vendredi 4 d=E9cembre 2020, 19:02:09 CET James Bottomley a =E9crit :
> On Fri, 2020-12-04 at 18:07 +0100, Ard Biesheuvel wrote:
> > On Fri, 4 Dec 2020 at 18:06, <laniel_francis@privacyrequired.com>
> >=20
> > wrote:
> > > From: Francis Laniel <laniel_francis@privacyrequired.com>
> > >=20
> > > 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.
> >=20
> > Why?
>=20
> 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
>=20
>     if (strstarts(option, "rgb")) {
>         option +=3D strlen("rgb");
>         ...
>=20
> with
>=20
>     len =3D str_has_prefix(option, "rgb");
>     if (len) {
>         option +=3D len
>         ...

The proposed changes were a bit mechanical and I did not think about using =
the=20
returned value in the way you proposed.
This a good idea though, so I can modify my patches to include this and sen=
d a=20
v2!
=20
> 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.

=46or the v2, should I only change cases where using str_has_prefix() bring=
s a=20
benefit over strstarts() or all the cases?

> James