linux-kernel - RE: [PATCH 2/2] block: add BLKSETDESCZONE ioctl for Zoned Block Devices

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Date:   Tue, 30 Jun 2020 13:28:07 +0000
From:   Matias Bjorling <Matias.Bjorling@....com>
To:     Bart Van Assche <bvanassche@....org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "kbusch@...nel.org" <kbusch@...nel.org>, "hch@....de" <hch@....de>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        Damien Le Moal <Damien.LeMoal@....com>,
        Niklas Cassel <Niklas.Cassel@....com>,
        Hans Holmberg <Hans.Holmberg@....com>
CC:     "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
Subject: RE: [PATCH 2/2] block: add BLKSETDESCZONE ioctl for Zoned Block
 Devices

> -----Original Message-----
> From: Bart Van Assche <bvanassche@....org>
> Sent: Monday, 29 June 2020 03.36
> To: Matias Bjorling <Matias.Bjorling@....com>; axboe@...nel.dk;
> kbusch@...nel.org; hch@....de; sagi@...mberg.me;
> martin.petersen@...cle.com; Damien Le Moal <Damien.LeMoal@....com>;
> Niklas Cassel <Niklas.Cassel@....com>; Hans Holmberg
> <Hans.Holmberg@....com>
> Cc: linux-scsi@...r.kernel.org; linux-kernel@...r.kernel.org; linux-
> block@...r.kernel.org; linux-nvme@...ts.infradead.org
> Subject: Re: [PATCH 2/2] block: add BLKSETDESCZONE ioctl for Zoned Block
> Devices
> 
> On 2020-06-28 16:01, Matias Bjørling wrote:
> > +	/* This may take a while, so be nice to others */
> > +	cond_resched();
> > +
> > +	return submit_bio_wait(&bio);
> 
> A cond_resched() call before a submit_bio_wait() call? I think it's the first time
> that I see this. Is that call really necessary? Isn't the
> wait_for_completion() call inside submit_bio_wait() sufficient?
> 

One can't be too careful these days, heh. I'll fix it up. Thanks!

> > +	/* no flags is currently supported */
>                     ^^
>                     are?
> 
> > +	/* allocate the size of the zone descriptor extension and fill
> > +	 * with the data in the user data buffer. If the data size is less
> > +	 * than the zone descriptor extension size, then the rest of the
> > +	 * zone description extension data buffer is zero-filled.
> > +	 */
> > +	zsd_data = (void *) get_zeroed_page(GFP_KERNEL);
> > +	if (!zsd_data)
> > +		return -ENOMEM;
> > +
> > +	if (copy_from_user(zsd_data, argp + sizeof(struct blk_zone_set_desc),
> > +			   zsd.len)) {
> > +		ret = -EFAULT;
> > +		goto free;
> > +	}
> 
> Has it been considered to use kmalloc() instead of get_zeroed_page()?
> 
> > diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
> > index ccb895f911b1..53b7b05b0004 100644
> > --- a/include/linux/blk_types.h
> > +++ b/include/linux/blk_types.h
> > @@ -316,6 +316,8 @@ enum req_opf {
> >  	REQ_OP_ZONE_FINISH	= 12,
> >  	/* write data at the current zone write pointer */
> >  	REQ_OP_ZONE_APPEND	= 13,
> > +	/* associate zone desc extension data to a zone */
> > +	REQ_OP_ZONE_SET_DESC	= 14,
> >
> >  	/* SCSI passthrough using struct scsi_request */
> >  	REQ_OP_SCSI_IN		= 32,
> 
> Does REQ_OP_ZONE_SET_DESC count as a read or as a write operation? See
> also:
> 
> static inline bool op_is_write(unsigned int op) {
> 	return (op & 1);
> }
> 
> > +/**
> > + * struct blk_zone_set_desc - BLKSETDESCZONE ioctl requests
> > + * @sector: Starting sector of the zone to operate on.
> > + * @flags: Feature flags.
> > + * @len: size, in bytes, of the data to be associated to the zone.
> > + * @data: data to be associated.
> > + */
> > +struct blk_zone_set_desc {
> > +	__u64		sector;
> > +	__u32		flags;
> > +	__u32		len;
> > +	__u8		data[0];
> > +};
> 
> Isn't the recommended style to use a flexible array ([] instead of [0])?
> See also
> https://lore.kernel.org/lkml/20200608213711.GA22271@embeddedor/.
> 
> Thanks,
> 
> Bart.