Re: [Nbd] [PATCH 1/7] block: export blkdev_reread_part() and __blkdev_reread_part()
- To: Peter Zijlstra <peterz@...1270...>
- Cc: Jens Axboe <axboe@...161...>, Stefan Weinhuber <wein@...1296...>, "nbd-general@lists.sourceforge.net" <nbd-general@lists.sourceforge.net>, linux-s390@...25..., Mike Galbraith <bitbucket@...1990...>, Stefan Haberland <stefan.haberland@...1296...>, Sebastian Ott <sebott@...1294...>, Linux Kernel Mailing List <linux-kernel@...25...>, Jarod Wilson <jarod@...696...>, Christoph Hellwig <hch@...1270...>, Fabian Frederick <fabf@...1980...>, Alexander Viro <viro@...1300...>, David Herrmann <dh.herrmann@...17...>, Tejun Heo <tj@...1285...>, Andrew Morton <akpm@...133...>
- Subject: Re: [Nbd] [PATCH 1/7] block: export blkdev_reread_part() and __blkdev_reread_part()
- From: Ming Lei <ming.lei@...1301...>
- Date: Wed, 8 Apr 2015 23:28:25 +0800
- Message-id: <CACVXFVN9Zdv77wVsTa5OxKz43u5z8L8vMMVTXhjtap2fTYsBwg@...18...>
- In-reply-to: <20150408150325.GJ5029@...1991...>
- References: <1428218688-4092-1-git-send-email-ming.lei@...1301...> <1428474226-27386-1-git-send-email-jarod@...696...> <1428474226-27386-2-git-send-email-jarod@...696...> <CACVXFVOQH_tNdBtgNH8UhLan304cSacRTzqvvRhndLauexTvaw@...18...> <20150408150325.GJ5029@...1991...>
On Wed, Apr 8, 2015 at 11:03 PM, Peter Zijlstra <peterz@...1270...> wrote:
> On Wed, Apr 08, 2015 at 10:50:56PM +0800, Ming Lei wrote:
>> > +/*
>> > + * This is an exported API for the block driver, and will not
>> > + * acquire bd_mutex, leaving it up to the caller to handle
>> > + * any necessary locking.
>>
>> Actually, the function is introduced and should be used in case
>> that bd_mutex has been held already, such as clearing fd in
>> loop release().
>>
>> > + */
>> > +int __blkdev_reread_part(struct block_device *bdev)
>> > {
>> > struct gendisk *disk = bdev->bd_disk;
>> >
>
> lockdep_assert_held(&bdev->bd_mutex);
>
> is an excellent means of avoiding that comment and verifying its
> actually true :-)
Exactly, and it has been added in my local tree, :-)
>
>> > if (!disk_part_scan_enabled(disk) || bdev != bdev->bd_contains)
>> > return -EINVAL;
>> > if (!capable(CAP_SYS_ADMIN))
>> > return -EACCES;
>> > +
>> > + return rescan_partitions(disk, bdev);
>> > +}
>> > +EXPORT_SYMBOL(__blkdev_reread_part);
>> > +
>> > +/*
>> > + * This is an exported API for the block driver, and will
>> > + * acquire bd_mutex. Make sure you aren't calling it with
>> > + * bd_mutex already held, or we'll return -EBUSY.
>>
>> Strictly speaking, it should be "Make sure you aren't calling it
>> with bd_mutex already held in current context".
>>
>> > + */
>> > +int blkdev_reread_part(struct block_device *bdev)
>> > +{
>> > + int res;
>> > +
>> > if (!mutex_trylock(&bdev->bd_mutex))
>> > return -EBUSY;
>
> Is that really needed? It seems rather poor form.
The trylock will be replaced with mutex_lock in patch 6.
>
>> > - res = rescan_partitions(disk, bdev);
>> > + res = __blkdev_reread_part(bdev);
>> > mutex_unlock(&bdev->bd_mutex);
>> > +
>> > return res;
>> > }
>> > +EXPORT_SYMBOL(blkdev_reread_part);
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