linux-kernel - Re: [PATCH v3 1/2] ubi: provide a way to skip CRC checks

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Date:   Mon, 02 Jul 2018 10:49:44 +0300
From:   Artem Bityutskiy <dedekind1@...il.com>
To:     Richard Weinberger <richard@....at>
Cc:     Quentin Schulz <quentin.schulz@...tlin.com>, dwmw2@...radead.org,
        computersforpeace@...il.com, boris.brezillon@...tlin.com,
        marek.vasut@...il.com, linux-mtd@...ts.infradead.org,
        linux-kernel@...r.kernel.org, thomas.petazzoni@...tlin.com
Subject: Re: [PATCH v3 1/2] ubi: provide a way to skip CRC checks

On Mon, 2018-07-02 at 09:43 +0200, Richard Weinberger wrote:
> Artem,
> 
> Am Montag, 2. Juli 2018, 09:30:25 CEST schrieb Artem Bityutskiy:
> > Hi,
> > 
> > On Thu, 2018-06-28 at 09:40 +0200, Quentin Schulz wrote:
> > > diff --git a/drivers/mtd/ubi/kapi.c b/drivers/mtd/ubi/kapi.c
> > > index d4b2e87..e9e9ecb 100644
> > > --- a/drivers/mtd/ubi/kapi.c
> > > +++ b/drivers/mtd/ubi/kapi.c
> > > @@ -202,7 +202,7 @@ struct ubi_volume_desc *ubi_open_volume(int
> > > ubi_num, int vol_id, int mode)
> > >  	desc->mode = mode;
> > >  
> > >  	mutex_lock(&ubi->ckvol_mutex);
> > > -	if (!vol->checked) {
> > > +	if (!vol->checked && !vol->skip_check) {
> > >  		/* This is the first open - check the volume */
> > >  		err = ubi_check_volume(ubi, vol_id);
> > >  		if (err < 0) {
> > 
> > Did you deliberately did not add a similar check to
> > 'vol_cdev_write()' ?
> > You want to skip checking on load but do have the checking after
> > volume update ?
> > Looks a bit inconsistent to me. At the very least deserves a
> > comment in
> > 'vol_cdev_write()' about why 'skip_check' flag is ignored there.
> 
> Well, the idea is skipping the check, not the crc32 on the medium.
> That way we can later, if needed, offer a way to drop the flag but
> and don't have to rewrite with crc32-enabled.

I understand that. I am talking about cdev.c line 370. We will check
the CRC after the update regardless of 'skip_check'. So I point out
that this is not very consistent with what we do in
'ubi_open_volume()'.

Is this deliberate or not? If this is deliberate, we should at least
add an explanation comment in 'vol_cdev_write()'.