diff mbox

[06/17] block: introduce GENHD_FL_HIDDEN

Message ID 20171018165258.23212-7-hch@lst.de (mailing list archive)
State New, archived
Headers show

Commit Message

Christoph Hellwig Oct. 18, 2017, 4:52 p.m. UTC 
With this flag a driver can create a gendisk that can be used for I/O
submission inside the kernel, but which is not registered as user
facing block device.  This will be useful for the NVMe multipath
implementation.

Signed-off-by: Christoph Hellwig <hch@lst.de>
---
 block/genhd.c         | 53 ++++++++++++++++++++++++++++++++++-----------------
 include/linux/genhd.h |  1 +
 2 files changed, 36 insertions(+), 18 deletions(-)

Comments

Johannes Thumshirn Oct. 19, 2017, 8:31 a.m. UTC | #1 
Looks good,
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Hannes Reinecke Oct. 19, 2017, 12:45 p.m. UTC | #2 
On 10/18/2017 06:52 PM, Christoph Hellwig wrote:
> With this flag a driver can create a gendisk that can be used for I/O
> submission inside the kernel, but which is not registered as user
> facing block device.  This will be useful for the NVMe multipath
> implementation.
> 
> Signed-off-by: Christoph Hellwig <hch@lst.de>
> ---
>  block/genhd.c         | 53 ++++++++++++++++++++++++++++++++++-----------------
>  include/linux/genhd.h |  1 +
>  2 files changed, 36 insertions(+), 18 deletions(-)
> 
To quote:

On Fri, Oct 06, 2017 at 09:13 AM, Christoph Hellwig wrote:
> On Fri, Oct 06, 2017 at 10:39:50AM +1100, NeilBrown wrote:
[ .. ]
>>
>> There is some precedent for hiding things from /proc/partitions.
>> removable devices like CDROMs are hidden, and you can easily hide
>> individual devices by setting GENHD_FL_SUPPRESS_PARTITION_INFO.
>> We might be able to get that through.  It is certainly worth writing
>> a patch and letting people experiment with it.
>
> No way in hell this would get through.  Preemptive NAK right here.
>
> That whole idea is just amazingly stupid, and no one has even
> explained a reason for it.

I wonder what has changed ...

Cheers,

Hannes
Christoph Hellwig Oct. 19, 2017, 1:15 p.m. UTC | #3 
On Thu, Oct 19, 2017 at 02:45:03PM +0200, Hannes Reinecke wrote:
> > No way in hell this would get through.  Preemptive NAK right here.
> >
> > That whole idea is just amazingly stupid, and no one has even
> > explained a reason for it.
> 
> I wonder what has changed ...

The nvme-controller devices aren't accessible to anyone outside the
nvme driver itself, so they aren't just hidden, as far as the rest
of the kernel is concerned they don't exist.  They just allow reusing
block layer code in the nvme driver instead of reimplementing it.
diff mbox

Patch

diff --git a/block/genhd.c b/block/genhd.c
index 1174d24e405e..0b28cd491b1d 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -585,6 +585,11 @@  static void register_disk(struct device *parent, struct gendisk *disk)
 	 */
 	pm_runtime_set_memalloc_noio(ddev, true);
 
+	if (disk->flags & GENHD_FL_HIDDEN) {
+		dev_set_uevent_suppress(ddev, 0);
+		return;
+	}
+
 	disk->part0.holder_dir = kobject_create_and_add("holders", &ddev->kobj);
 	disk->slave_dir = kobject_create_and_add("slaves", &ddev->kobj);
 
@@ -616,6 +621,11 @@  static void register_disk(struct device *parent, struct gendisk *disk)
 	while ((part = disk_part_iter_next(&piter)))
 		kobject_uevent(&part_to_dev(part)->kobj, KOBJ_ADD);
 	disk_part_iter_exit(&piter);
+
+	err = sysfs_create_link(&ddev->kobj,
+				&disk->queue->backing_dev_info->dev->kobj,
+				"bdi");
+	WARN_ON(err);
 }
 
 /**
@@ -630,7 +640,6 @@  static void register_disk(struct device *parent, struct gendisk *disk)
  */
 void device_add_disk(struct device *parent, struct gendisk *disk)
 {
-	struct backing_dev_info *bdi;
 	dev_t devt;
 	int retval;
 
@@ -639,7 +648,8 @@  void device_add_disk(struct device *parent, struct gendisk *disk)
 	 * parameters make sense.
 	 */
 	WARN_ON(disk->minors && !(disk->major || disk->first_minor));
-	WARN_ON(!disk->minors && !(disk->flags & GENHD_FL_EXT_DEVT));
+	WARN_ON(!disk->minors &&
+		!(disk->flags & (GENHD_FL_EXT_DEVT | GENHD_FL_HIDDEN)));
 
 	disk->flags |= GENHD_FL_UP;
 
@@ -648,18 +658,26 @@  void device_add_disk(struct device *parent, struct gendisk *disk)
 		WARN_ON(1);
 		return;
 	}
-	disk_to_dev(disk)->devt = devt;
 	disk->major = MAJOR(devt);
 	disk->first_minor = MINOR(devt);
 
 	disk_alloc_events(disk);
 
-	/* Register BDI before referencing it from bdev */
-	bdi = disk->queue->backing_dev_info;
-	bdi_register_owner(bdi, disk_to_dev(disk));
-
-	blk_register_region(disk_devt(disk), disk->minors, NULL,
-			    exact_match, exact_lock, disk);
+	if (disk->flags & GENHD_FL_HIDDEN) {
+		/*
+		 * Don't let hidden disks show up in /proc/partitions,
+		 * and don't bother scanning for partitions either.
+		 */
+		disk->flags |= GENHD_FL_SUPPRESS_PARTITION_INFO;
+		disk->flags |= GENHD_FL_NO_PART_SCAN;
+	} else {
+		/* Register BDI before referencing it from bdev */
+		disk_to_dev(disk)->devt = devt;
+		bdi_register_owner(disk->queue->backing_dev_info,
+				disk_to_dev(disk));
+		blk_register_region(disk_devt(disk), disk->minors, NULL,
+				    exact_match, exact_lock, disk);
+	}
 	register_disk(parent, disk);
 	blk_register_queue(disk);
 
@@ -669,10 +687,6 @@  void device_add_disk(struct device *parent, struct gendisk *disk)
 	 */
 	WARN_ON_ONCE(!blk_get_queue(disk->queue));
 
-	retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
-				   "bdi");
-	WARN_ON(retval);
-
 	disk_add_events(disk);
 	blk_integrity_add(disk);
 }
@@ -701,7 +715,8 @@  void del_gendisk(struct gendisk *disk)
 	set_capacity(disk, 0);
 	disk->flags &= ~GENHD_FL_UP;
 
-	sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
+	if (!(disk->flags & GENHD_FL_HIDDEN))
+		sysfs_remove_link(&disk_to_dev(disk)->kobj, "bdi");
 	if (disk->queue) {
 		/*
 		 * Unregister bdi before releasing device numbers (as they can
@@ -712,13 +727,15 @@  void del_gendisk(struct gendisk *disk)
 	} else {
 		WARN_ON(1);
 	}
-	blk_unregister_region(disk_devt(disk), disk->minors);
+
+	if (!(disk->flags & GENHD_FL_HIDDEN)) {
+		blk_unregister_region(disk_devt(disk), disk->minors);
+		kobject_put(disk->part0.holder_dir);
+		kobject_put(disk->slave_dir);
+	}
 
 	part_stat_set_all(&disk->part0, 0);
 	disk->part0.stamp = 0;
-
-	kobject_put(disk->part0.holder_dir);
-	kobject_put(disk->slave_dir);
 	if (!sysfs_deprecated)
 		sysfs_remove_link(block_depr, dev_name(disk_to_dev(disk)));
 	pm_runtime_set_memalloc_noio(disk_to_dev(disk), false);
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 5c0ed5db33c2..93aae3476f58 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -140,6 +140,7 @@  struct hd_struct {
 #define GENHD_FL_NATIVE_CAPACITY		128
 #define GENHD_FL_BLOCK_EVENTS_ON_EXCL_WRITE	256
 #define GENHD_FL_NO_PART_SCAN			512
+#define GENHD_FL_HIDDEN				1024
 
 enum {
 	DISK_EVENT_MEDIA_CHANGE			= 1 << 0, /* media changed */