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 06:59:36 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     "Elliott, Robert (Servers)" <elliott@....com>
Cc:     'Matteo Croce' <mcroce@...ux.microsoft.com>,
        "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 Gonz?lez <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, Jul 12, 2021 at 07:22:43PM +0000, Elliott, Robert (Servers) wrote:
>     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?

Why would it not work?  put_user is a magic macro that works on all
scalar value.