[PATCH] block: remove the "detected capacity change" message

[PATCH] block: remove the "detected capacity change" message

[Mikulas Patocka]

Every time a new device mapper device is created, a message "detected
capacity change from 0 to 2097152" is reported. This message is useless,
so this patch removes it.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 block/genhd.c |    3 ---
 1 file changed, 3 deletions(-)

Index: linux-2.6/block/genhd.c
===================================================================
--- linux-2.6.orig/block/genhd.c	2021-03-17 11:03:52.000000000 +0100
+++ linux-2.6/block/genhd.c	2021-03-17 11:04:27.000000000 +0100
@@ -72,9 +72,6 @@ bool set_capacity_and_notify(struct gend
 	    (disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
 		return false;
 
-	pr_info("%s: detected capacity change from %lld to %lld\n",
-		disk->disk_name, capacity, size);
-
 	/*
 	 * Historically we did not send a uevent for changes to/from an empty
 	 * device.

[dm-devel] [PATCH] block: remove the "detected capacity change" message

[Mikulas Patocka]

Every time a new device mapper device is created, a message "detected
capacity change from 0 to 2097152" is reported. This message is useless,
so this patch removes it.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

---
 block/genhd.c |    3 ---
 1 file changed, 3 deletions(-)

Index: linux-2.6/block/genhd.c
===================================================================
--- linux-2.6.orig/block/genhd.c	2021-03-17 11:03:52.000000000 +0100
+++ linux-2.6/block/genhd.c	2021-03-17 11:04:27.000000000 +0100
@@ -72,9 +72,6 @@ bool set_capacity_and_notify(struct gend
 	    (disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
 		return false;
 
-	pr_info("%s: detected capacity change from %lld to %lld\n",
-		disk->disk_name, capacity, size);
-
 	/*
 	 * Historically we did not send a uevent for changes to/from an empty
 	 * device.

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Re: [PATCH] block: remove the "detected capacity change" message

[Christoph Hellwig]

No, it is everything but useless.  It is not needed during device
creation, but that is something that the GENHD_FL_UP check should catch.

You should probably audit the device mapper code why it sets the initial
capacity when the gendisk is up already, as that can cause all kinds of
problems.  If the setting of the initial capacity after add_disk is
indeed intentional you can switch to set_capacity(), but you should
probably document the rationale in a detailed comment.

Re: [dm-devel] [PATCH] block: remove the "detected capacity change" message

[Christoph Hellwig]

No, it is everything but useless.  It is not needed during device
creation, but that is something that the GENHD_FL_UP check should catch.

You should probably audit the device mapper code why it sets the initial
capacity when the gendisk is up already, as that can cause all kinds of
problems.  If the setting of the initial capacity after add_disk is
indeed intentional you can switch to set_capacity(), but you should
probably document the rationale in a detailed comment.

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Re: [PATCH] block: remove the "detected capacity change" message

[Mikulas Patocka]

On Wed, 17 Mar 2021, Christoph Hellwig wrote:

> No, it is everything but useless.  It is not needed during device
> creation, but that is something that the GENHD_FL_UP check should catch.
> 
> You should probably audit the device mapper code why it sets the initial
> capacity when the gendisk is up already, as that can cause all kinds of
> problems.  If the setting of the initial capacity after add_disk is
> indeed intentional you can switch to set_capacity(), but you should
> probably document the rationale in a detailed comment.

BTW. the loop device has the same problem as device mapper - it also 
prints "loop0: detected capacity change from 0 to 2097152" when it is 
being activated.

Would you accept this patch?

Or do you think that we should change device mapper and the loopback 
driver to call "set_capacity" on the initial device creation?

Mikulas

---
 block/genhd.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6/block/genhd.c
===================================================================
--- linux-2.6.orig/block/genhd.c	2021-03-17 16:26:11.000000000 +0100
+++ linux-2.6/block/genhd.c	2021-03-17 16:26:42.000000000 +0100
@@ -71,16 +71,16 @@ bool set_capacity_and_notify(struct gend
 	if (size == capacity ||
 	    (disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
 		return false;
-
-	pr_info("%s: detected capacity change from %lld to %lld\n",
-		disk->disk_name, capacity, size);
-
 	/*
 	 * Historically we did not send a uevent for changes to/from an empty
 	 * device.
 	 */
 	if (!capacity || !size)
 		return false;
+
+	pr_info("%s: detected capacity change from %lld to %lld\n",
+		disk->disk_name, capacity, size);
+
 	kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
 	return true;
 }

Re: [dm-devel] [PATCH] block: remove the "detected capacity change" message

[Mikulas Patocka]

On Wed, 17 Mar 2021, Christoph Hellwig wrote:

> No, it is everything but useless.  It is not needed during device
> creation, but that is something that the GENHD_FL_UP check should catch.
> 
> You should probably audit the device mapper code why it sets the initial
> capacity when the gendisk is up already, as that can cause all kinds of
> problems.  If the setting of the initial capacity after add_disk is
> indeed intentional you can switch to set_capacity(), but you should
> probably document the rationale in a detailed comment.

BTW. the loop device has the same problem as device mapper - it also 
prints "loop0: detected capacity change from 0 to 2097152" when it is 
being activated.

Would you accept this patch?

Or do you think that we should change device mapper and the loopback 
driver to call "set_capacity" on the initial device creation?

Mikulas

---
 block/genhd.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

Index: linux-2.6/block/genhd.c
===================================================================
--- linux-2.6.orig/block/genhd.c	2021-03-17 16:26:11.000000000 +0100
+++ linux-2.6/block/genhd.c	2021-03-17 16:26:42.000000000 +0100
@@ -71,16 +71,16 @@ bool set_capacity_and_notify(struct gend
 	if (size == capacity ||
 	    (disk->flags & (GENHD_FL_UP | GENHD_FL_HIDDEN)) != GENHD_FL_UP)
 		return false;
-
-	pr_info("%s: detected capacity change from %lld to %lld\n",
-		disk->disk_name, capacity, size);
-
 	/*
 	 * Historically we did not send a uevent for changes to/from an empty
 	 * device.
 	 */
 	if (!capacity || !size)
 		return false;
+
+	pr_info("%s: detected capacity change from %lld to %lld\n",
+		disk->disk_name, capacity, size);
+
 	kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
 	return true;
 }

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