[net-next] devlink: report maximum number of snapshots with regions

Each region has an independently configurable number of maximum
snapshots. This information is not reported to userspace, making it not
very discoverable. Fix this by adding a new
DEVLINK_ATTR_REGION_MAX_SNAPSHOST attribute which is used to report this
maximum.

Ex:

  $devlink region
  pci/0000:af:00.0/nvm-flash: size 10485760 snapshot [] max 1
  pci/0000:af:00.0/device-caps: size 4096 snapshot [] max 10
  pci/0000:af:00.1/nvm-flash: size 10485760 snapshot [] max 1
  pci/0000:af:00.1/device-caps: size 4096 snapshot [] max 10

This information enables users to understand why a new region command
may fail due to having too many existing snapshots.

Reported-by: Gurucharan G <redacted> (A Contingent worker at Intel)
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
---
I realized while explaining a new devlink region that there is no mechanism
to view the maximum snapshot count for a given region without analyzing the
code for a driver. This change fixes that.

 Documentation/networking/devlink/devlink-region.rst | 4 ++--
 Documentation/networking/devlink/ice.rst            | 4 ++++
 include/uapi/linux/devlink.h                        | 2 ++
 net/core/devlink.c                                  | 5 +++++
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/Documentation/networking/devlink/devlink-region.rst b/Documentation/networking/devlink/devlink-region.rst
index 58fe95e9a49d..f06dca9a1eb6 100644
--- a/Documentation/networking/devlink/devlink-region.rst
+++ b/Documentation/networking/devlink/devlink-region.rst

@@ -44,8 +44,8 @@ example usage
 
     # Show all of the exposed regions with region sizes:
     $ devlink region show
-    pci/0000:00:05.0/cr-space: size 1048576 snapshot [1 2]
-    pci/0000:00:05.0/fw-health: size 64 snapshot [1 2]
+    pci/0000:00:05.0/cr-space: size 1048576 snapshot [1 2] max 8
+    pci/0000:00:05.0/fw-health: size 64 snapshot [1 2] max 8
 
     # Delete a snapshot using:
     $ devlink region del pci/0000:00:05.0/cr-space snapshot 1

diff --git a/Documentation/networking/devlink/ice.rst b/Documentation/networking/devlink/ice.rst
index a432dc419fa4..32aea1f7d7f7 100644
--- a/Documentation/networking/devlink/ice.rst
+++ b/Documentation/networking/devlink/ice.rst

@@ -141,6 +141,10 @@ Users can request an immediate capture of a snapshot via the
 
 .. code:: shell
 
+    $ devlink region show
+    pci/0000:01:00.0/nvm-flash: size 10485760 snapshot [] max 1
+    pci/0000:01:00.0/device-caps: size 4096 snapshot [] max 10
+
     $ devlink region new pci/0000:01:00.0/nvm-flash snapshot 1
     $ devlink region dump pci/0000:01:00.0/nvm-flash snapshot 1
 

diff --git a/include/uapi/linux/devlink.h b/include/uapi/linux/devlink.h
index 32f53a0069d6..b897b80770f6 100644
--- a/include/uapi/linux/devlink.h
+++ b/include/uapi/linux/devlink.h

@@ -551,6 +551,8 @@ enum devlink_attr {
 	DEVLINK_ATTR_RATE_NODE_NAME,		/* string */
 	DEVLINK_ATTR_RATE_PARENT_NODE_NAME,	/* string */
 
+	DEVLINK_ATTR_REGION_MAX_SNAPSHOTS,	/* u32 */
+
 	/* add new attributes above here, update the policy in devlink.c */
 
 	__DEVLINK_ATTR_MAX,

diff --git a/net/core/devlink.c b/net/core/devlink.c
index b64303085d0e..4917112406a0 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c

@@ -5078,6 +5078,11 @@ static int devlink_nl_region_fill(struct sk_buff *msg, struct devlink *devlink,
 	if (err)
 		goto nla_put_failure;
 
+	err = nla_put_u32(msg, DEVLINK_ATTR_REGION_MAX_SNAPSHOTS,
+			  region->max_snapshots);
+	if (err)
+		goto nla_put_failure;
+
 	err = devlink_nl_region_snapshots_id_put(msg, devlink, region);
 	if (err)
 		goto nla_put_failure;

base-commit: b05173028cc52384be42dcf81abdb4133caccfa5
-- 
2.31.1.331.gb0c09ab8796f

On Thu, 30 Sep 2021 14:21:04 -0700 Jacob Keller wrote:

Each region has an independently configurable number of maximum
snapshots. This information is not reported to userspace, making it not
very discoverable. Fix this by adding a new
DEVLINK_ATTR_REGION_MAX_SNAPSHOST attribute which is used to report this
maximum.

Ex:

  $devlink region
  pci/0000:af:00.0/nvm-flash: size 10485760 snapshot [] max 1
  pci/0000:af:00.0/device-caps: size 4096 snapshot [] max 10
  pci/0000:af:00.1/nvm-flash: size 10485760 snapshot [] max 1
  pci/0000:af:00.1/device-caps: size 4096 snapshot [] max 10

This information enables users to understand why a new region command
may fail due to having too many existing snapshots.

Reported-by: Gurucharan G <redacted> (A Contingent worker at Intel)
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>

Acked-by: Jakub Kicinski <kuba@kernel.org>

Hello:

This patch was applied to netdev/net-next.git (refs/heads/master):

On Thu, 30 Sep 2021 14:21:04 -0700 you wrote:

Each region has an independently configurable number of maximum
snapshots. This information is not reported to userspace, making it not
very discoverable. Fix this by adding a new
DEVLINK_ATTR_REGION_MAX_SNAPSHOST attribute which is used to report this
maximum.

Ex:

[...]

Here is the summary with links:
  - [net-next] devlink: report maximum number of snapshots with regions
    https://git.kernel.org/netdev/net-next/c/a70e3f024d5f

You are awesome, thank you!
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