linux-kernel - Re: [PATCH] VFS: filename_create(): fix incorrect intent.

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Message-ID: <20220331114949.02fae137@suse.de>
Date:   Thu, 31 Mar 2022 11:49:49 +0200
From:   David Disseldorp <ddiss@...e.de>
To:     "NeilBrown" <neilb@...e.de>
Cc:     "Al Viro" <viro@...iv.linux.org.uk>, linux-nfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org,
        "LKML" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] VFS: filename_create(): fix incorrect intent.

On Thu, 31 Mar 2022 09:59:48 +1100, NeilBrown wrote:

> On Wed, 30 Mar 2022, David Disseldorp wrote:
> > Hi Neil,
> > 
> > I gave this a spin and was wondering why xfstests wouldn't start with
> > this change...
> > 
> > On Mon, 28 Mar 2022 11:56:48 +1100, NeilBrown wrote:
> > ...  
> > > 
> > > diff --git a/fs/namei.c b/fs/namei.c
> > > index 3f1829b3ab5b..3ffb42e56a8e 100644
> > > --- a/fs/namei.c
> > > +++ b/fs/namei.c
> > > @@ -3676,7 +3676,6 @@ static struct dentry *filename_create(int dfd, struct filename *name,
> > >  	int type;
> > >  	int err2;
> > >  	int error;
> > > -	bool is_dir = (lookup_flags & LOOKUP_DIRECTORY);
> > >  
> > >  	/*
> > >  	 * Note that only LOOKUP_REVAL and LOOKUP_DIRECTORY matter here. Any
> > > @@ -3698,9 +3697,11 @@ static struct dentry *filename_create(int dfd, struct filename *name,
> > >  	/* don't fail immediately if it's r/o, at least try to report other errors */
> > >  	err2 = mnt_want_write(path->mnt);
> > >  	/*
> > > -	 * Do the final lookup.
> > > +	 * Do the final lookup.  Request 'create' only if there is no trailing
> > > +	 * '/', or if directory is requested.
> > >  	 */
> > > -	lookup_flags |= LOOKUP_CREATE | LOOKUP_EXCL;
> > > +	if (!last.name[last.len] || (lookup_flags & LOOKUP_DIRECTORY))
> > > +		lookup_flags |= LOOKUP_CREATE | LOOKUP_EXCL;  
> > 
> > This doesn't look right, as any LOOKUP_DIRECTORY flag gets dropped via
> > the prior "lookup_flags &= LOOKUP_REVAL;".  
> 
> Arg.. thanks for testing - I clearly should have tested more broadly.
> 
> I could leave the "is_dir" variable there I guess.
> Or maybe the masking statement should be 
>     lookup_flags &= LOOKUP_REVAL | LOOKUP_DIRECTORY;
> as that is a better match for the comment.

Modifying "lookup_flags" results in changed filename_parentat() and
__lookup_hash() parameters, which isn't an intended consequence IIUC. I
think retaining "is_dir" would make sense.

Cheers, David