linux-kernel - Re: [PATCH v4 3/5] block: add ioctl to read the disk sequence number

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Date:   Tue, 13 Jul 2021 01:25:22 +0200
From:   Matteo Croce <mcroce@...ux.microsoft.com>
To:     "Elliott, Robert (Servers)" <elliott@....com>
Cc:     "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        Jens Axboe <axboe@...nel.dk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Lennart Poettering" <lennart@...ttering.net>,
        Luca Boccassi <bluca@...ian.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Damien Le Moal <damien.lemoal@....com>,
        Tejun Heo <tj@...nel.org>,
        Javier González <javier@...igon.com>,
        Niklas Cassel <niklas.cassel@....com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Hannes Reinecke <hare@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        JeffleXu <jefflexu@...ux.alibaba.com>
Subject: Re: [PATCH v4 3/5] block: add ioctl to read the disk sequence
 number

On Mon, 12 Jul 2021 19:22:43 +0000
"Elliott, Robert (Servers)" <elliott@....com> wrote:

> 
> 
> > -----Original Message-----
> > From: Matteo Croce <mcroce@...ux.microsoft.com>
> > Sent: Sunday, July 11, 2021 12:54 PM
> ...
> > Subject: [PATCH v4 3/5] block: add ioctl to read the disk sequence
> > number
> > 
> > From: Matteo Croce <mcroce@...rosoft.com>
> > 
> > Add a new BLKGETDISKSEQ ioctl which retrieves the disk sequence
> > number from the genhd structure.
> ...
> 
> 
> Given:
>     static int put_u64(u64 __user *argp, u64 val)
>     {
>         return put_user(val, argp);
>     }
> 
> > diff --git a/block/ioctl.c b/block/ioctl.c
> > index 24beec9ca9c9..0c3a4a53fa11 100644
> > --- a/block/ioctl.c
> > +++ b/block/ioctl.c
> > @@ -469,6 +469,8 @@ static int blkdev_common_ioctl(struct
> > block_device *bdev, fmode_t mode,
> >  				BLKDEV_DISCARD_SECURE);
> ...
> 
> > +	case BLKGETDISKSEQ:
> > +		return put_u64(argp, bdev->bd_disk->diskseq);
> 
> How does that work on a system in which int is 32 bits?
> 
> 

Hi,

what's the difference with this?

	case BLKGETSIZE64:
		return put_u64(argp, i_size_read(bdev->bd_inode));

The returned int is an error code, not the diskseq value itself, e.g.

	case BLKFRAGET:
		if (!argp)
			return -EINVAL;

Regards,
-- 
per aspera ad upstream