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

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Message-ID: <CALTww29CN4iqmneiAG31kZDBubCMop=gg299hdW-TXCNq1c4gQ@mail.gmail.com>
Date:   Thu, 30 Mar 2023 12:55:07 +0800
From:   Xiao Ni <xni@...hat.com>
To:     NeilBrown <neilb@...e.de>
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, Mar 30, 2023 at 11:15 AM NeilBrown <neilb@...e.de> wrote:
>
> 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
>

That's right, thanks for this explanation :)

-- 
Best Regards
Xiao Ni