linux-kernel - Re: [PATCH - mdadm] mdopen: always try create_named

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Message-id: <168014613094.14629.7292916705339147692@noble.neil.brown.name>
Date:   Thu, 30 Mar 2023 14:15:30 +1100
From:   "NeilBrown" <neilb@...e.de>
To:     "Xiao Ni" <xni@...hat.com>
Cc:     "Jes Sorensen" <jes@...ined-monkey.org>,
        "Mariusz Tkaczyk" <mariusz.tkaczyk@...ux.intel.com>,
        "Song Liu" <song@...nel.org>,
        "Linux regressions mailing list" <regressions@...ts.linux.dev>,
        "linux-raid" <linux-raid@...r.kernel.org>,
        "LKML" <linux-kernel@...r.kernel.org>,
        "Nikolay Kichukov" <hijacker@...um.net>
Subject: Re: [PATCH - mdadm] mdopen: always try create_named_array()

On Thu, 30 Mar 2023, Xiao Ni wrote:
> On Thu, Mar 30, 2023 at 5:52 AM NeilBrown <neilb@...e.de> wrote:
> >
> > On Wed, 22 Mar 2023, NeilBrown wrote:
> > > On Wed, 22 Mar 2023, Xiao Ni wrote:
> > >
> > > >
> > > > Second, are there possibilities that the arguments "dev" and "name" of
> > > > function create_mddev
> > > > are null at the same time?
> > >
> > > No.  For Build or Create, dev is never NULL.  For Assemble and
> > > Incremental, name is never NULL.
> > >
> >
> > I should clarify this a bit.  For Assemble and Incremental, "name" is
> > never NULL *but* it might be an empty string.
> > So:
> >         if (name && name[0] == 0)
> >                 name = NULL;
> >
> > might cause it to become NULL.  So you cannot assume there is always
> > either a valid "dev" or a valid "name".  "dev" might be NULL, and "name"
> > might be "".
> >
> > NeilBrown
> >
> 
> Hi Neil
> 
> The input argument name should be the metadata name. For incremental
> and assemble, why are there possibilities that the metadata name is
> invalid? A raid device should have a valid metadata name, right?

"should" do, yes.  But you can never completely trust data on disk.  It
is safest to be prepared for "name" being "".

NeilBrown