[SRU,Xenial,Artful,Bionic,v2,1/1] UBUNTU: SAUCE: (no-up) bcache: decouple emitting a cached_dev CHANGE uevent

From: Ryan Harper <ryan.harper@canonical.com>

BugLink: http://bugs.launchpad.net/bugs/1729145

- decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
  and dev.label from bch_cached_dev_run() which only happens when a
  bcacheX device is bound to the actual backing block device (bcache0 -> vdb)

- update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
  needed; no functional code path changes here

- Modify register_bcache to detect a re-registering of a bcache
  cached_dev, and in that case call bcache_cached_dev_emit_change() to

Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
---
 drivers/md/bcache/bcache.h |  1 +
 drivers/md/bcache/super.c  | 53 +++++++++++++++++++++++++++++++++++++---------
 2 files changed, 44 insertions(+), 10 deletions(-)

On 11.12.2017 15:12, Joseph Salisbury wrote:
> From: Ryan Harper <ryan.harper@canonical.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1729145
> 
> - decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
>   and dev.label from bch_cached_dev_run() which only happens when a
>   bcacheX device is bound to the actual backing block device (bcache0 -> vdb)
> 
> - update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
>   needed; no functional code path changes here
> 
> - Modify register_bcache to detect a re-registering of a bcache
>   cached_dev, and in that case call bcache_cached_dev_emit_change() to
> 
> Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
> Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>

> ---
>  drivers/md/bcache/bcache.h |  1 +
>  drivers/md/bcache/super.c  | 53 +++++++++++++++++++++++++++++++++++++---------
>  2 files changed, 44 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 02619ca..8ed7e7a 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -906,6 +906,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size);
>  
>  int bch_cached_dev_attach(struct cached_dev *, struct cache_set *);
>  void bch_cached_dev_detach(struct cached_dev *);
> +void bch_cached_dev_emit_change(struct cached_dev *);
>  void bch_cached_dev_run(struct cached_dev *);
>  void bcache_device_stop(struct bcache_device *);
>  
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 04608da..9ff0aac 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -834,7 +834,7 @@ static void calc_cached_dev_sectors(struct cache_set *c)
>  	c->cached_dev_sectors = sectors;
>  }
>  
> -void bch_cached_dev_run(struct cached_dev *dc)
> +void bch_cached_dev_emit_change(struct cached_dev *dc)
>  {
>  	struct bcache_device *d = &dc->disk;
>  	char buf[SB_LABEL_SIZE + 1];
> @@ -849,9 +849,18 @@ void bch_cached_dev_run(struct cached_dev *dc)
>  	buf[SB_LABEL_SIZE] = '\0';
>  	env[2] = kasprintf(GFP_KERNEL, "CACHED_LABEL=%s", buf);
>  
> +	/* won't show up in the uevent file, use udevadm monitor -e instead
> +	 * only class / kset properties are persistent */
> +	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
> +	kfree(env[1]);
> +	kfree(env[2]);
> +
> +}
> +
> +void bch_cached_dev_run(struct cached_dev *dc)
> +{
> +	struct bcache_device *d = &dc->disk;
>  	if (atomic_xchg(&dc->running, 1)) {
> -		kfree(env[1]);
> -		kfree(env[2]);
>  		return;
>  	}
>  
> @@ -867,11 +876,9 @@ void bch_cached_dev_run(struct cached_dev *dc)
>  
>  	add_disk(d->disk);
>  	bd_link_disk_holder(dc->bdev, dc->disk.disk);
> -	/* won't show up in the uevent file, use udevadm monitor -e instead
> -	 * only class / kset properties are persistent */
> -	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
> -	kfree(env[1]);
> -	kfree(env[2]);
> +
> +	/* emit change event */
> +	bch_cached_dev_emit_change(dc);
>  
>  	if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
>  	    sysfs_create_link(&disk_to_dev(d->disk)->kobj, &d->kobj, "bcache"))
> @@ -1916,6 +1923,21 @@ static bool bch_is_open_backing(struct block_device *bdev) {
>  	return false;
>  }
>  
> +static struct cached_dev *bch_find_cached_dev(struct block_device *bdev) {
> +	struct cache_set *c, *tc;
> +	struct cached_dev *dc, *t;
> +
> +	list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
> +		list_for_each_entry_safe(dc, t, &c->cached_devs, list)
> +			if (dc->bdev == bdev)
> +				return dc;
> +	list_for_each_entry_safe(dc, t, &uncached_devices, list)
> +		if (dc->bdev == bdev)
> +			return dc;
> +
> +	return NULL;
> +}
> +
>  static bool bch_is_open_cache(struct block_device *bdev) {
>  	struct cache_set *c, *tc;
>  	struct cache *ca;
> @@ -1941,6 +1963,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>  	struct cache_sb *sb = NULL;
>  	struct block_device *bdev = NULL;
>  	struct page *sb_page = NULL;
> +	struct cached_dev *dc = NULL;
>  
>  	if (!try_module_get(THIS_MODULE))
>  		return -EBUSY;
> @@ -1957,10 +1980,20 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>  		if (bdev == ERR_PTR(-EBUSY)) {
>  			bdev = lookup_bdev(strim(path), 0);
>  			mutex_lock(&bch_register_lock);
> -			if (!IS_ERR(bdev) && bch_is_open(bdev))
> +			if (!IS_ERR(bdev) && bch_is_open(bdev)) {
>  				err = "device already registered";
> -			else
> +				/* emit CHANGE event for backing devices to export
> +				 * CACHED_{UUID/LABEL} values to udev */
> +				if (bch_is_open_backing(bdev)) {
> +					dc = bch_find_cached_dev(bdev);
> +					if (dc) {
> +						bch_cached_dev_emit_change(dc);
> +						err = "device already registered (emitting change event)";
> +					}
> +				}
> +			} else {
>  				err = "device busy";
> +            }
>  			mutex_unlock(&bch_register_lock);
>  			if (!IS_ERR(bdev))
>  				bdput(bdev);
>

On 11/12/17 14:12, Joseph Salisbury wrote:
> From: Ryan Harper <ryan.harper@canonical.com>
> 
> BugLink: http://bugs.launchpad.net/bugs/1729145
> 
> - decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
>   and dev.label from bch_cached_dev_run() which only happens when a
>   bcacheX device is bound to the actual backing block device (bcache0 -> vdb)
> 
> - update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
>   needed; no functional code path changes here
> 
> - Modify register_bcache to detect a re-registering of a bcache
>   cached_dev, and in that case call bcache_cached_dev_emit_change() to
> 
> Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
> Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
> ---
>  drivers/md/bcache/bcache.h |  1 +
>  drivers/md/bcache/super.c  | 53 +++++++++++++++++++++++++++++++++++++---------
>  2 files changed, 44 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> index 02619ca..8ed7e7a 100644
> --- a/drivers/md/bcache/bcache.h
> +++ b/drivers/md/bcache/bcache.h
> @@ -906,6 +906,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size);
>  
>  int bch_cached_dev_attach(struct cached_dev *, struct cache_set *);
>  void bch_cached_dev_detach(struct cached_dev *);
> +void bch_cached_dev_emit_change(struct cached_dev *);
>  void bch_cached_dev_run(struct cached_dev *);
>  void bcache_device_stop(struct bcache_device *);
>  
> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> index 04608da..9ff0aac 100644
> --- a/drivers/md/bcache/super.c
> +++ b/drivers/md/bcache/super.c
> @@ -834,7 +834,7 @@ static void calc_cached_dev_sectors(struct cache_set *c)
>  	c->cached_dev_sectors = sectors;
>  }
>  
> -void bch_cached_dev_run(struct cached_dev *dc)
> +void bch_cached_dev_emit_change(struct cached_dev *dc)
>  {
>  	struct bcache_device *d = &dc->disk;
>  	char buf[SB_LABEL_SIZE + 1];
> @@ -849,9 +849,18 @@ void bch_cached_dev_run(struct cached_dev *dc)
>  	buf[SB_LABEL_SIZE] = '\0';
>  	env[2] = kasprintf(GFP_KERNEL, "CACHED_LABEL=%s", buf);
>  
> +	/* won't show up in the uevent file, use udevadm monitor -e instead
> +	 * only class / kset properties are persistent */
> +	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
> +	kfree(env[1]);
> +	kfree(env[2]);
> +
> +}
> +
> +void bch_cached_dev_run(struct cached_dev *dc)
> +{
> +	struct bcache_device *d = &dc->disk;
>  	if (atomic_xchg(&dc->running, 1)) {
> -		kfree(env[1]);
> -		kfree(env[2]);
>  		return;
>  	}
>  
> @@ -867,11 +876,9 @@ void bch_cached_dev_run(struct cached_dev *dc)
>  
>  	add_disk(d->disk);
>  	bd_link_disk_holder(dc->bdev, dc->disk.disk);
> -	/* won't show up in the uevent file, use udevadm monitor -e instead
> -	 * only class / kset properties are persistent */
> -	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
> -	kfree(env[1]);
> -	kfree(env[2]);
> +
> +	/* emit change event */
> +	bch_cached_dev_emit_change(dc);
>  
>  	if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
>  	    sysfs_create_link(&disk_to_dev(d->disk)->kobj, &d->kobj, "bcache"))
> @@ -1916,6 +1923,21 @@ static bool bch_is_open_backing(struct block_device *bdev) {
>  	return false;
>  }
>  
> +static struct cached_dev *bch_find_cached_dev(struct block_device *bdev) {
> +	struct cache_set *c, *tc;
> +	struct cached_dev *dc, *t;
> +
> +	list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
> +		list_for_each_entry_safe(dc, t, &c->cached_devs, list)
> +			if (dc->bdev == bdev)
> +				return dc;
> +	list_for_each_entry_safe(dc, t, &uncached_devices, list)
> +		if (dc->bdev == bdev)
> +			return dc;
> +
> +	return NULL;
> +}
> +
>  static bool bch_is_open_cache(struct block_device *bdev) {
>  	struct cache_set *c, *tc;
>  	struct cache *ca;
> @@ -1941,6 +1963,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>  	struct cache_sb *sb = NULL;
>  	struct block_device *bdev = NULL;
>  	struct page *sb_page = NULL;
> +	struct cached_dev *dc = NULL;
>  
>  	if (!try_module_get(THIS_MODULE))
>  		return -EBUSY;
> @@ -1957,10 +1980,20 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>  		if (bdev == ERR_PTR(-EBUSY)) {
>  			bdev = lookup_bdev(strim(path), 0);
>  			mutex_lock(&bch_register_lock);
> -			if (!IS_ERR(bdev) && bch_is_open(bdev))
> +			if (!IS_ERR(bdev) && bch_is_open(bdev)) {
>  				err = "device already registered";
> -			else
> +				/* emit CHANGE event for backing devices to export
> +				 * CACHED_{UUID/LABEL} values to udev */
> +				if (bch_is_open_backing(bdev)) {
> +					dc = bch_find_cached_dev(bdev);
> +					if (dc) {
> +						bch_cached_dev_emit_change(dc);
> +						err = "device already registered (emitting change event)";
> +					}
> +				}
> +			} else {
>  				err = "device busy";
> +            }
>  			mutex_unlock(&bch_register_lock);
>  			if (!IS_ERR(bdev))
>  				bdput(bdev);
> 

Positive test results for Bionic. Looks reasonable to me.

Will this be sent upstream at some point?

Acked-by: Colin Ian King <colin.king@canonical.com>

On Tue, Jan 23, 2018 at 02:33:31PM +0000, Colin Ian King wrote:
> On 11/12/17 14:12, Joseph Salisbury wrote:
> > From: Ryan Harper <ryan.harper@canonical.com>
> > 
> > BugLink: http://bugs.launchpad.net/bugs/1729145
> > 
> > - decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
> >   and dev.label from bch_cached_dev_run() which only happens when a
> >   bcacheX device is bound to the actual backing block device (bcache0 -> vdb)
> > 
> > - update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
> >   needed; no functional code path changes here
> > 
> > - Modify register_bcache to detect a re-registering of a bcache
> >   cached_dev, and in that case call bcache_cached_dev_emit_change() to
> > 
> > Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
> > Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
> > ---
> >  drivers/md/bcache/bcache.h |  1 +
> >  drivers/md/bcache/super.c  | 53 +++++++++++++++++++++++++++++++++++++---------
> >  2 files changed, 44 insertions(+), 10 deletions(-)
> > 
> > diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> > index 02619ca..8ed7e7a 100644
> > --- a/drivers/md/bcache/bcache.h
> > +++ b/drivers/md/bcache/bcache.h
> > @@ -906,6 +906,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size);
> >  
> >  int bch_cached_dev_attach(struct cached_dev *, struct cache_set *);
> >  void bch_cached_dev_detach(struct cached_dev *);
> > +void bch_cached_dev_emit_change(struct cached_dev *);
> >  void bch_cached_dev_run(struct cached_dev *);
> >  void bcache_device_stop(struct bcache_device *);
> >  
> > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> > index 04608da..9ff0aac 100644
> > --- a/drivers/md/bcache/super.c
> > +++ b/drivers/md/bcache/super.c
> > @@ -834,7 +834,7 @@ static void calc_cached_dev_sectors(struct cache_set *c)
> >  	c->cached_dev_sectors = sectors;
> >  }
> >  
> > -void bch_cached_dev_run(struct cached_dev *dc)
> > +void bch_cached_dev_emit_change(struct cached_dev *dc)
> >  {
> >  	struct bcache_device *d = &dc->disk;
> >  	char buf[SB_LABEL_SIZE + 1];
> > @@ -849,9 +849,18 @@ void bch_cached_dev_run(struct cached_dev *dc)
> >  	buf[SB_LABEL_SIZE] = '\0';
> >  	env[2] = kasprintf(GFP_KERNEL, "CACHED_LABEL=%s", buf);
> >  
> > +	/* won't show up in the uevent file, use udevadm monitor -e instead
> > +	 * only class / kset properties are persistent */
> > +	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
> > +	kfree(env[1]);
> > +	kfree(env[2]);
> > +
> > +}
> > +
> > +void bch_cached_dev_run(struct cached_dev *dc)
> > +{
> > +	struct bcache_device *d = &dc->disk;
> >  	if (atomic_xchg(&dc->running, 1)) {
> > -		kfree(env[1]);
> > -		kfree(env[2]);
> >  		return;
> >  	}
> >  
> > @@ -867,11 +876,9 @@ void bch_cached_dev_run(struct cached_dev *dc)
> >  
> >  	add_disk(d->disk);
> >  	bd_link_disk_holder(dc->bdev, dc->disk.disk);
> > -	/* won't show up in the uevent file, use udevadm monitor -e instead
> > -	 * only class / kset properties are persistent */
> > -	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
> > -	kfree(env[1]);
> > -	kfree(env[2]);
> > +
> > +	/* emit change event */
> > +	bch_cached_dev_emit_change(dc);
> >  
> >  	if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
> >  	    sysfs_create_link(&disk_to_dev(d->disk)->kobj, &d->kobj, "bcache"))
> > @@ -1916,6 +1923,21 @@ static bool bch_is_open_backing(struct block_device *bdev) {
> >  	return false;
> >  }
> >  
> > +static struct cached_dev *bch_find_cached_dev(struct block_device *bdev) {
> > +	struct cache_set *c, *tc;
> > +	struct cached_dev *dc, *t;
> > +
> > +	list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
> > +		list_for_each_entry_safe(dc, t, &c->cached_devs, list)
> > +			if (dc->bdev == bdev)
> > +				return dc;
> > +	list_for_each_entry_safe(dc, t, &uncached_devices, list)
> > +		if (dc->bdev == bdev)
> > +			return dc;
> > +
> > +	return NULL;
> > +}
> > +
> >  static bool bch_is_open_cache(struct block_device *bdev) {
> >  	struct cache_set *c, *tc;
> >  	struct cache *ca;
> > @@ -1941,6 +1963,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
> >  	struct cache_sb *sb = NULL;
> >  	struct block_device *bdev = NULL;
> >  	struct page *sb_page = NULL;
> > +	struct cached_dev *dc = NULL;
> >  
> >  	if (!try_module_get(THIS_MODULE))
> >  		return -EBUSY;
> > @@ -1957,10 +1980,20 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
> >  		if (bdev == ERR_PTR(-EBUSY)) {
> >  			bdev = lookup_bdev(strim(path), 0);
> >  			mutex_lock(&bch_register_lock);
> > -			if (!IS_ERR(bdev) && bch_is_open(bdev))
> > +			if (!IS_ERR(bdev) && bch_is_open(bdev)) {
> >  				err = "device already registered";
> > -			else
> > +				/* emit CHANGE event for backing devices to export
> > +				 * CACHED_{UUID/LABEL} values to udev */
> > +				if (bch_is_open_backing(bdev)) {
> > +					dc = bch_find_cached_dev(bdev);
> > +					if (dc) {
> > +						bch_cached_dev_emit_change(dc);
> > +						err = "device already registered (emitting change event)";
> > +					}
> > +				}
> > +			} else {
> >  				err = "device busy";
> > +            }
> >  			mutex_unlock(&bch_register_lock);
> >  			if (!IS_ERR(bdev))
> >  				bdput(bdev);
> > 
> 
> Positive test results for Bionic. Looks reasonable to me.
> 
> Will this be sent upstream at some point?

+1 to this question. This is a userspace-visible change in behavior, so
I'm somewhat hesitant to apply it if the behavior won't also change
upstream.

On 01/23/2018 11:27 AM, Seth Forshee wrote:
> On Tue, Jan 23, 2018 at 02:33:31PM +0000, Colin Ian King wrote:
>> On 11/12/17 14:12, Joseph Salisbury wrote:
>>> From: Ryan Harper <ryan.harper@canonical.com>
>>>
>>> BugLink: http://bugs.launchpad.net/bugs/1729145
>>>
>>> - decouple emitting a cached_dev CHANGE uevent which includes dev.uuid
>>>   and dev.label from bch_cached_dev_run() which only happens when a
>>>   bcacheX device is bound to the actual backing block device (bcache0 -> vdb)
>>>
>>> - update bch_cached_dev_run() to invoke bch_cached_dev_emit_change() as
>>>   needed; no functional code path changes here
>>>
>>> - Modify register_bcache to detect a re-registering of a bcache
>>>   cached_dev, and in that case call bcache_cached_dev_emit_change() to
>>>
>>> Signed-off-by: Ryan Harper <ryan.harper@canonical.com>
>>> Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
>>> ---
>>>  drivers/md/bcache/bcache.h |  1 +
>>>  drivers/md/bcache/super.c  | 53 +++++++++++++++++++++++++++++++++++++---------
>>>  2 files changed, 44 insertions(+), 10 deletions(-)
>>>
>>> diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
>>> index 02619ca..8ed7e7a 100644
>>> --- a/drivers/md/bcache/bcache.h
>>> +++ b/drivers/md/bcache/bcache.h
>>> @@ -906,6 +906,7 @@ int bch_flash_dev_create(struct cache_set *c, uint64_t size);
>>>  
>>>  int bch_cached_dev_attach(struct cached_dev *, struct cache_set *);
>>>  void bch_cached_dev_detach(struct cached_dev *);
>>> +void bch_cached_dev_emit_change(struct cached_dev *);
>>>  void bch_cached_dev_run(struct cached_dev *);
>>>  void bcache_device_stop(struct bcache_device *);
>>>  
>>> diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
>>> index 04608da..9ff0aac 100644
>>> --- a/drivers/md/bcache/super.c
>>> +++ b/drivers/md/bcache/super.c
>>> @@ -834,7 +834,7 @@ static void calc_cached_dev_sectors(struct cache_set *c)
>>>  	c->cached_dev_sectors = sectors;
>>>  }
>>>  
>>> -void bch_cached_dev_run(struct cached_dev *dc)
>>> +void bch_cached_dev_emit_change(struct cached_dev *dc)
>>>  {
>>>  	struct bcache_device *d = &dc->disk;
>>>  	char buf[SB_LABEL_SIZE + 1];
>>> @@ -849,9 +849,18 @@ void bch_cached_dev_run(struct cached_dev *dc)
>>>  	buf[SB_LABEL_SIZE] = '\0';
>>>  	env[2] = kasprintf(GFP_KERNEL, "CACHED_LABEL=%s", buf);
>>>  
>>> +	/* won't show up in the uevent file, use udevadm monitor -e instead
>>> +	 * only class / kset properties are persistent */
>>> +	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
>>> +	kfree(env[1]);
>>> +	kfree(env[2]);
>>> +
>>> +}
>>> +
>>> +void bch_cached_dev_run(struct cached_dev *dc)
>>> +{
>>> +	struct bcache_device *d = &dc->disk;
>>>  	if (atomic_xchg(&dc->running, 1)) {
>>> -		kfree(env[1]);
>>> -		kfree(env[2]);
>>>  		return;
>>>  	}
>>>  
>>> @@ -867,11 +876,9 @@ void bch_cached_dev_run(struct cached_dev *dc)
>>>  
>>>  	add_disk(d->disk);
>>>  	bd_link_disk_holder(dc->bdev, dc->disk.disk);
>>> -	/* won't show up in the uevent file, use udevadm monitor -e instead
>>> -	 * only class / kset properties are persistent */
>>> -	kobject_uevent_env(&disk_to_dev(d->disk)->kobj, KOBJ_CHANGE, env);
>>> -	kfree(env[1]);
>>> -	kfree(env[2]);
>>> +
>>> +	/* emit change event */
>>> +	bch_cached_dev_emit_change(dc);
>>>  
>>>  	if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
>>>  	    sysfs_create_link(&disk_to_dev(d->disk)->kobj, &d->kobj, "bcache"))
>>> @@ -1916,6 +1923,21 @@ static bool bch_is_open_backing(struct block_device *bdev) {
>>>  	return false;
>>>  }
>>>  
>>> +static struct cached_dev *bch_find_cached_dev(struct block_device *bdev) {
>>> +	struct cache_set *c, *tc;
>>> +	struct cached_dev *dc, *t;
>>> +
>>> +	list_for_each_entry_safe(c, tc, &bch_cache_sets, list)
>>> +		list_for_each_entry_safe(dc, t, &c->cached_devs, list)
>>> +			if (dc->bdev == bdev)
>>> +				return dc;
>>> +	list_for_each_entry_safe(dc, t, &uncached_devices, list)
>>> +		if (dc->bdev == bdev)
>>> +			return dc;
>>> +
>>> +	return NULL;
>>> +}
>>> +
>>>  static bool bch_is_open_cache(struct block_device *bdev) {
>>>  	struct cache_set *c, *tc;
>>>  	struct cache *ca;
>>> @@ -1941,6 +1963,7 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>>>  	struct cache_sb *sb = NULL;
>>>  	struct block_device *bdev = NULL;
>>>  	struct page *sb_page = NULL;
>>> +	struct cached_dev *dc = NULL;
>>>  
>>>  	if (!try_module_get(THIS_MODULE))
>>>  		return -EBUSY;
>>> @@ -1957,10 +1980,20 @@ static ssize_t register_bcache(struct kobject *k, struct kobj_attribute *attr,
>>>  		if (bdev == ERR_PTR(-EBUSY)) {
>>>  			bdev = lookup_bdev(strim(path), 0);
>>>  			mutex_lock(&bch_register_lock);
>>> -			if (!IS_ERR(bdev) && bch_is_open(bdev))
>>> +			if (!IS_ERR(bdev) && bch_is_open(bdev)) {
>>>  				err = "device already registered";
>>> -			else
>>> +				/* emit CHANGE event for backing devices to export
>>> +				 * CACHED_{UUID/LABEL} values to udev */
>>> +				if (bch_is_open_backing(bdev)) {
>>> +					dc = bch_find_cached_dev(bdev);
>>> +					if (dc) {
>>> +						bch_cached_dev_emit_change(dc);
>>> +						err = "device already registered (emitting change event)";
>>> +					}
>>> +				}
>>> +			} else {
>>>  				err = "device busy";
>>> +            }
>>>  			mutex_unlock(&bch_register_lock);
>>>  			if (!IS_ERR(bdev))
>>>  				bdput(bdev);
>>>
>> Positive test results for Bionic. Looks reasonable to me.
>>
>> Will this be sent upstream at some point?
> +1 to this question. This is a userspace-visible change in behavior, so
> I'm somewhat hesitant to apply it if the behavior won't also change
> upstream.
>
I'll submit this upstream for Ryan.