linux-kernel - RE: [PATCH] exfat: retain 'VolumeFlags' properly

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Date:   Tue, 14 Jul 2020 01:56:23 +0000
From:   "Kohada.Tetsuhiro@...MitsubishiElectric.co.jp" 
        <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>
To:     'Namjae Jeon' <namjae.jeon@...sung.com>
CC:     "Mori.Takahiro@...MitsubishiElectric.co.jp" 
        <Mori.Takahiro@...MitsubishiElectric.co.jp>,
        "Motai.Hirotaka@...MitsubishiElectric.co.jp" 
        <Motai.Hirotaka@...MitsubishiElectric.co.jp>,
        'Sungjong Seo' <sj1557.seo@...sung.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        'Tetsuhiro Kohada'' <kohada.t2@...il.com>
Subject: RE: [PATCH] exfat: retain 'VolumeFlags' properly

Thanks for your reply.

> > Also, rename ERR_MEDIUM to MED_FAILURE.
> I think that MEDIA_FAILURE looks better.

I think so too.
If so, should I change VOL_DIRTY to VOLUME_DIRTY?

> > -int exfat_set_vol_flags(struct super_block *sb, unsigned short
> > new_flag)
> > +int exfat_set_vol_flags(struct super_block *sb, unsigned short
> > +new_flags)
> >  {
> >  	struct exfat_sb_info *sbi = EXFAT_SB(sb);
> >  	struct boot_sector *p_boot = (struct boot_sector *)sbi->boot_bh->b_data;
> >  	bool sync;
> If dirty bit is set in on-disk volume flags, we can just return 0 at the beginning of this function ?

That's right.
Neither 'set VOL_DIRTY' nor 'set VOL_CLEAN' makes a change to volume flags.


> > +	if (new_flags == VOL_CLEAN)
> > +		new_flags = (sbi->vol_flags & ~VOL_DIRTY) | sbi->vol_flags_noclear;
> > +	else
> > +		new_flags |= sbi->vol_flags;
> > +
> >  	/* flags are not changed */
> > -	if (sbi->vol_flag == new_flag)
> > +	if (sbi->vol_flags == new_flags)
> >  		return 0;
> >
> > -	sbi->vol_flag = new_flag;
> > +	sbi->vol_flags = new_flags;
> >
> >  	/* skip updating volume dirty flag,
> >  	 * if this volume has been mounted with read-only @@ -114,9 +119,9
> > @@ int exfat_set_vol_flags(struct super_block *sb, unsigned short new_flag)
> >  	if (sb_rdonly(sb))
> >  		return 0;
> >
> > -	p_boot->vol_flags = cpu_to_le16(new_flag);
> > +	p_boot->vol_flags = cpu_to_le16(new_flags);
> How about set or clear only dirty bit to on-disk volume flags instead of using
> sbi->vol_flags_noclear ?
>        if (set)
>                p_boot->vol_flags |= cpu_to_le16(VOL_DIRTY);
>        else
>                p_boot->vol_flags &= cpu_to_le16(~VOL_DIRTY);

In this way, the initial  VOL_DIRTY cannot be retained.
The purpose of this patch is to avoid losing the initial VOL_DIRTY and MED_FAILURE.
Furthermore, I'm also thinking of setting MED_FAILURE.

However, the formula for 'new_flags' may be a bit complicated.
Is it better to change to the following?

	if (new_flags == VOL_CLEAN)
		new_flags = sbi->vol_flags & ~VOL_DIRTY
	else
		new_flags |= sbi->vol_flags;

	new_flags |= sbi->vol_flags_noclear;


one more point,
Is there a better name than 'vol_flags_noclear'?
(I can't come up with a good name anymore)

BR
---
Kohada Tetsuhiro <Kohada.Tetsuhiro@...MitsubishiElectric.co.jp>