From: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
To: Hannes Reinecke <hare@suse.de>
Cc: linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
Christoph Hellwig <hch@lst.de>, Jens Axboe <axboe@fb.com>
Subject: Re: [PATCH 4/4] block: expose devt for GENHD_FL_HIDDEN disks
Date: Thu, 13 Dec 2018 09:41:25 -0200 [thread overview]
Message-ID: <20181213114124.GB7543@calabresa> (raw)
In-Reply-To: <b3ef062d-3bc3-fdf8-f395-31d1822a3192@suse.de>
On Thu, Dec 13, 2018 at 10:18:40AM +0100, Hannes Reinecke wrote:
> On 12/6/18 5:48 PM, Thadeu Lima de Souza Cascardo wrote:
> > Without this exposure, lsblk will fail as it tries to find out the
> > device's dev_t numbers. This causes a real problem for nvme multipath
> > devices, as their slaves are hidden.
> >
> > Exposing them fixes the problem, even though trying to open the devices
> > returns an error in the case of nvme multipath. So, right now, it's the
> > driver's responsibility to return a failure to open hidden devices.
> >
> > Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>
> > ---
> > block/genhd.c | 9 ++++-----
> > 1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/block/genhd.c b/block/genhd.c
> > index 7674fce32fca..65a7fa664188 100644
> > --- a/block/genhd.c
> > +++ b/block/genhd.c
> > @@ -687,6 +687,7 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
> > disk_alloc_events(disk);
> > + disk_to_dev(disk)->devt = devt;
> > if (disk->flags & GENHD_FL_HIDDEN) {
> > /*
> > * Don't let hidden disks show up in /proc/partitions,
> > @@ -698,13 +699,12 @@ static void __device_add_disk(struct device *parent, struct gendisk *disk,
> > int ret;
> > /* Register BDI before referencing it from bdev */
> > - disk_to_dev(disk)->devt = devt;
> > ret = bdi_register_owner(disk->queue->backing_dev_info,
> > disk_to_dev(disk));
> > WARN_ON(ret);
> > - blk_register_region(disk_devt(disk), disk->minors, NULL,
> > - exact_match, exact_lock, disk);
> > }
> > + blk_register_region(disk_devt(disk), disk->minors, NULL,
> > + exact_match, exact_lock, disk);
> > register_disk(parent, disk, groups);
> > if (register_queue)
> > blk_register_queue(disk);
> > @@ -776,8 +776,7 @@ void del_gendisk(struct gendisk *disk)
> > WARN_ON(1);
> > }
> > - if (!(disk->flags & GENHD_FL_HIDDEN))
> > - blk_unregister_region(disk_devt(disk), disk->minors);
> > + blk_unregister_region(disk_devt(disk), disk->minors);
> > kobject_put(disk->part0.holder_dir);
> > kobject_put(disk->slave_dir);
> >
> Welll ... this is not just 'lsblk', but more importantly this will force
> udev to create _block_ device nodes for the hidden devices, essentially
> 'unhide' them.
>
> Is this what we want?
> Christoph?
> I thought the entire _point_ of having hidden devices is that the are ...
> well ... hidden ...
>
I knew this would be the most controversial patch. And I had other solutions as
well, but preferred this one. So, the other alternative would be just not use
GENHD_FL_HIDDEN for the nvme devices, which would leave that flag without a
single user in the kernel. That would still fix the two problems
(initramfs-tools and lsblk), and not create any other problem I know of. That
patch would still fail to open the underlying devices when there is a
head/multipath associated with it.
So, the only thing GENHD_FL_HIDDEN gives us is saving some resources, like bdi,
for example. And we could also use it to fail open when blkdev_get* is called.
Of couse, that would still imply that its name should be changed, but as we
already have an attribute named after that, I find it hard to suggest such a
change.
Cascardo.
> Cheers,
>
> Hannes
> --
> Dr. Hannes Reinecke Teamlead Storage & Networking
> hare@suse.de +49 911 74053 688
> SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
> GF: F. Imendörffer, J. Smithard, J. Guild, D. Upmanyu, G. Norton
> HRB 21284 (AG Nürnberg)
next prev parent reply other threads:[~2018-12-13 11:41 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-06 16:48 [PATCH 0/4] nvme multipath: expose slaves/holders Thadeu Lima de Souza Cascardo
2018-12-06 16:48 ` [PATCH 1/4] block: move holder tracking from struct block_device to hd_struct Thadeu Lima de Souza Cascardo
2018-12-13 9:14 ` Hannes Reinecke
2018-12-06 16:48 ` [PATCH 2/4] nvme: create slaves/holder entries for multipath devices Thadeu Lima de Souza Cascardo
2018-12-13 9:15 ` Hannes Reinecke
2018-12-06 16:48 ` [PATCH 3/4] nvme: Should not warn when a disk path is opened Thadeu Lima de Souza Cascardo
2018-12-13 9:16 ` Hannes Reinecke
2018-12-06 16:48 ` [PATCH 4/4] block: expose devt for GENHD_FL_HIDDEN disks Thadeu Lima de Souza Cascardo
2018-12-06 20:22 ` Christoph Hellwig
2018-12-12 8:32 ` Christoph Hellwig
2018-12-12 12:39 ` Thadeu Lima de Souza Cascardo
2018-12-13 9:18 ` Hannes Reinecke
2018-12-13 11:41 ` Thadeu Lima de Souza Cascardo [this message]
2018-12-13 12:19 ` Hannes Reinecke
2018-12-13 16:08 ` Thadeu Lima de Souza Cascardo
2018-12-13 14:32 ` Christoph Hellwig
2018-12-13 15:25 ` Thadeu Lima de Souza Cascardo
2018-12-13 20:20 ` Christoph Hellwig
2018-12-13 21:00 ` Thadeu Lima de Souza Cascardo
2018-12-14 7:47 ` Hannes Reinecke
2018-12-14 8:56 ` Thadeu Lima de Souza Cascardo
2018-12-14 9:06 ` Thadeu Lima de Souza Cascardo
2018-12-14 9:54 ` Hannes Reinecke
2018-12-14 10:18 ` Hannes Reinecke
2018-12-14 11:09 ` Thadeu Lima de Souza Cascardo
2018-12-14 9:44 ` Hannes Reinecke
2018-12-13 9:33 ` [PATCH 0/4] nvme multipath: expose slaves/holders Johannes Thumshirn
2018-12-13 11:35 ` Thadeu Lima de Souza Cascardo
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