linux-ext4 - Re: [PATCH v3 RESEND] fcntl: Add 32bit filesystem mode

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Date:   Wed, 18 Nov 2020 00:38:41 +0100
From:   Linus Walleij <linus.walleij@...aro.org>
To:     Dave Martin <Dave.Martin@....com>
Cc:     "Theodore Ts'o" <tytso@....edu>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        QEMU Developers <qemu-devel@...gnu.org>,
        Florian Weimer <fw@...eb.enyo.de>,
        Peter Maydell <peter.maydell@...aro.org>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH v3 RESEND] fcntl: Add 32bit filesystem mode

On Tue, Oct 13, 2020 at 11:22 AM Dave Martin <Dave.Martin@....com> wrote:

> >       case F_SETFD:
> >               err = 0;
> >               set_close_on_exec(fd, arg & FD_CLOEXEC);
> > +             if (arg & FD_32BIT_MODE)
> > +                     filp->f_mode |= FMODE_32BITHASH;
> > +             else
> > +                     filp->f_mode &= ~FMODE_32BITHASH;
>
> This seems inconsistent?  F_SETFD is for setting flags on a file
> descriptor.  Won't setting a flag on filp here instead cause the
> behaviour to change for all file descriptors across the system that are
> open on this struct file?  Compare set_close_on_exec().
>
> I don't see any discussion on whether this should be an F_SETFL or an
> F_SETFD, though I see F_SETFD was Ted's suggestion originally.

I cannot honestly say I know the semantic difference.

I would ask the QEMU people how a user program would expect
the flag to behave.

Yours,
Linus Walleij