Re: [Nbd] [PATCH 1/6] block: export blkdev_reread_part()
- To: Ming Lei <ming.lei@...1301...>
- Cc: Jens Axboe <axboe@...161...>, "nbd-general@lists.sourceforge.net" <nbd-general@lists.sourceforge.net>, linux-s390@...25..., Stefan Haberland <stefan.haberland@...1296...>, Sebastian Ott <sebott@...1294...>, Linux Kernel Mailing List <linux-kernel@...25...>, 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 1/6] block: export blkdev_reread_part()
- From: Jarod Wilson <jarod@...696...>
- Date: Mon, 6 Apr 2015 09:48:43 -0400
- Message-id: <20150406134843.GF14217@...696...>
- In-reply-to: <20150406134227.GC14217@...696...>
- References: <1428218688-4092-1-git-send-email-ming.lei@...1301...> <1428218688-4092-2-git-send-email-ming.lei@...1301...> <20150405161241.GB16886@...1270...> <CACVXFVP-rokGRrMus_QXju+MVzFPTaFC45oZBe2PEBfbid8nmQ@...18...> <20150406134227.GC14217@...696...>
On Mon, Apr 06, 2015 at 09:42:27AM -0400, Jarod Wilson wrote:
> On Mon, Apr 06, 2015 at 12:40:12AM +0800, Ming Lei wrote:
> > On Mon, Apr 6, 2015 at 12:12 AM, Christoph Hellwig <hch@...1270...> wrote:
> > >> +/*
> > >> + * This is exported as API for block driver, can be called
> > >> + * with requiring bd_mutex or not.
> > >> + */
> > >> +int __blkdev_reread_part(struct block_device *bdev, bool lock)
> > >> {
> > >> struct gendisk *disk = bdev->bd_disk;
> > >> int res;
> > >> @@ -159,12 +163,14 @@ static int blkdev_reread_part(struct block_device *bdev)
> > >> return -EINVAL;
> > >> if (!capable(CAP_SYS_ADMIN))
> > >> return -EACCES;
> > >> - if (!mutex_trylock(&bdev->bd_mutex))
> > >> + if (lock && !mutex_trylock(&bdev->bd_mutex))
> > >> return -EBUSY;
> > >
> > > Please don't add funtions that do conditional locking, instead move
> > > all the code into blkdev_reread_part_nolock, and then wrap it:
> > >
> > > int blkdev_reread_part(struct block_device *bdev)
> > > {
> > > if (!mutex_trylock(&bdev->bd_mutex))
> > > return -EBUSY;
> > > blkdev_reread_part_nolock(bdev);
> > > mutex_unlock(&bdev->bd_mutex);
> > > }
> >
> > Yes, it is more clean, but with extra acquiring lock cost for the
> > failure cases, especially when we replace trylock with mutex_lock().
>
> I was working on a version of this myself over the past few days, I
> actually removed blkdev_reread_part() entirely, renamed
> fs/partition-generic.c::reread_partitions() to __reread_partitions(), then
Sorry, that was block/partition-generic.c, not fs/.
--
Jarod Wilson
jarod@...696...
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