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Message-Id: <20221123203834.738606-7-jacob.e.keller@intel.com>
Date:   Wed, 23 Nov 2022 12:38:31 -0800
From:   Jacob Keller <jacob.e.keller@...el.com>
To:     netdev@...r.kernel.org
Cc:     Jacob Keller <jacob.e.keller@...el.com>,
        Jiri Pirko <jiri@...dia.com>, Jakub Kicinski <kuba@...nel.org>
Subject: [PATCH net-next v2 6/9] devlink: support directly reading from region memory

To read from a region, user space must currently request a new snapshot of
the region and then read from that snapshot. This can sometimes be overkill
if user space only reads a tiny portion. They first create the snapshot,
then request a read, then destroy the snapshot.

For regions which have a single underlying "contents", it makes sense to
allow supporting direct reading of the region data.

Extend the DEVLINK_CMD_REGION_READ to allow direct reading from a region if
supported. Instead of reporting a missing snapshot id as invalid, check if
the region supports direct read and if so switch to the direct access
method for reading the region data.

Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>
---
Changes since v1:
* Update documentation to explain that direct reads are not atomic

 .../networking/devlink/devlink-region.rst     | 11 ++++
 include/net/devlink.h                         | 16 +++++
 net/core/devlink.c                            | 66 ++++++++++++++-----
 3 files changed, 76 insertions(+), 17 deletions(-)

diff --git a/Documentation/networking/devlink/devlink-region.rst b/Documentation/networking/devlink/devlink-region.rst
index f06dca9a1eb6..6525a9120a4e 100644
--- a/Documentation/networking/devlink/devlink-region.rst
+++ b/Documentation/networking/devlink/devlink-region.rst
@@ -31,6 +31,13 @@ in its ``devlink_region_ops`` structure. If snapshot id is not set in
 the ``DEVLINK_CMD_REGION_NEW`` request kernel will allocate one and send
 the snapshot information to user space.
 
+Regions may optionally allow directly reading from their contents without a
+snapshot. Direct read requests are not atomic. In particular a read request
+of size 256 bytes or larger will be split into multiple chunks. If atomic
+access is required, use a snapshot. A driver wishing to enable this for a
+region should implement the ``.read`` callback in the ``devlink_region_ops``
+structure.
+
 example usage
 -------------
 
@@ -65,6 +72,10 @@ example usage
     $ devlink region read pci/0000:00:05.0/fw-health snapshot 1 address 0 length 16
     0000000000000000 0014 95dc 0014 9514 0035 1670 0034 db30
 
+    # Read from the region without a snapshot
+    $ devlink region read pci/0000:00:05.0/fw-health address 16 length 16
+    0000000000000010 0000 0000 ffff ff04 0029 8c00 0028 8cc8
+
 As regions are likely very device or driver specific, no generic regions are
 defined. See the driver-specific documentation files for information on the
 specific regions a driver supports.
diff --git a/include/net/devlink.h b/include/net/devlink.h
index 074a79b8933f..02528f736f65 100644
--- a/include/net/devlink.h
+++ b/include/net/devlink.h
@@ -650,6 +650,10 @@ struct devlink_info_req;
  *            the data variable must be updated to point to the snapshot data.
  *            The function will be called while the devlink instance lock is
  *            held.
+ * @read: callback to directly read a portion of the region. On success,
+ *        the data pointer will be updated with the contents of the
+ *        requested portion of the region. The function will be called
+ *        while the devlink instance lock is held.
  * @priv: Pointer to driver private data for the region operation
  */
 struct devlink_region_ops {
@@ -659,6 +663,10 @@ struct devlink_region_ops {
 			const struct devlink_region_ops *ops,
 			struct netlink_ext_ack *extack,
 			u8 **data);
+	int (*read)(struct devlink *devlink,
+		    const struct devlink_region_ops *ops,
+		    struct netlink_ext_ack *extack,
+		    u64 offset, u32 size, u8 *data);
 	void *priv;
 };
 
@@ -670,6 +678,10 @@ struct devlink_region_ops {
  *            the data variable must be updated to point to the snapshot data.
  *            The function will be called while the devlink instance lock is
  *            held.
+ * @read: callback to directly read a portion of the region. On success,
+ *        the data pointer will be updated with the contents of the
+ *        requested portion of the region. The function will be called
+ *        while the devlink instance lock is held.
  * @priv: Pointer to driver private data for the region operation
  */
 struct devlink_port_region_ops {
@@ -679,6 +691,10 @@ struct devlink_port_region_ops {
 			const struct devlink_port_region_ops *ops,
 			struct netlink_ext_ack *extack,
 			u8 **data);
+	int (*read)(struct devlink_port *port,
+		    const struct devlink_port_region_ops *ops,
+		    struct netlink_ext_ack *extack,
+		    u64 offset, u32 size, u8 *data);
 	void *priv;
 };
 
diff --git a/net/core/devlink.c b/net/core/devlink.c
index 729e2162a4db..f249b5b57677 100644
--- a/net/core/devlink.c
+++ b/net/core/devlink.c
@@ -6515,6 +6515,26 @@ devlink_region_snapshot_fill(void *cb_priv, u8 *chunk, u32 chunk_size,
 	return 0;
 }
 
+static int
+devlink_region_port_direct_fill(void *cb_priv, u8 *chunk, u32 chunk_size,
+				u64 curr_offset, struct netlink_ext_ack *extack)
+{
+	struct devlink_region *region = cb_priv;
+
+	return region->port_ops->read(region->port, region->port_ops, extack,
+				      curr_offset, chunk_size, chunk);
+}
+
+static int
+devlink_region_direct_fill(void *cb_priv, u8 *chunk, u32 chunk_size,
+			   u64 curr_offset, struct netlink_ext_ack *extack)
+{
+	struct devlink_region *region = cb_priv;
+
+	return region->ops->read(region->devlink, region->ops, extack,
+				 curr_offset, chunk_size, chunk);
+}
+
 static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 					     struct netlink_callback *cb)
 {
@@ -6523,12 +6543,12 @@ static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 	u64 ret_offset, start_offset, end_offset = U64_MAX;
 	struct nlattr **attrs = info->attrs;
 	struct devlink_port *port = NULL;
-	struct devlink_snapshot *snapshot;
+	devlink_chunk_fill_t *region_cb;
 	struct devlink_region *region;
 	const char *region_name;
 	struct devlink *devlink;
 	unsigned int index;
-	u32 snapshot_id;
+	void *region_cb_priv;
 	void *hdr;
 	int err;
 
@@ -6546,12 +6566,6 @@ static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 		goto out_unlock;
 	}
 
-	if (!attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID]) {
-		NL_SET_ERR_MSG(cb->extack, "No snapshot id provided");
-		err = -EINVAL;
-		goto out_unlock;
-	}
-
 	if (info->attrs[DEVLINK_ATTR_PORT_INDEX]) {
 		index = nla_get_u32(info->attrs[DEVLINK_ATTR_PORT_INDEX]);
 
@@ -6577,12 +6591,30 @@ static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 	}
 
 	snapshot_attr = attrs[DEVLINK_ATTR_REGION_SNAPSHOT_ID];
-	snapshot_id = nla_get_u32(snapshot_attr);
-	snapshot = devlink_region_snapshot_get_by_id(region, snapshot_id);
-	if (!snapshot) {
-		NL_SET_ERR_MSG_ATTR(cb->extack, snapshot_attr, "requested snapshot does not exist");
-		err = -EINVAL;
-		goto out_unlock;
+	if (!snapshot_attr) {
+		if (!region->ops->read) {
+			NL_SET_ERR_MSG(cb->extack, "requested region does not support direct read");
+			err = -EOPNOTSUPP;
+			goto out_unlock;
+		}
+		if (port)
+			region_cb = &devlink_region_port_direct_fill;
+		else
+			region_cb = &devlink_region_direct_fill;
+		region_cb_priv = region;
+	} else {
+		struct devlink_snapshot *snapshot;
+		u32 snapshot_id;
+
+		snapshot_id = nla_get_u32(snapshot_attr);
+		snapshot = devlink_region_snapshot_get_by_id(region, snapshot_id);
+		if (!snapshot) {
+			NL_SET_ERR_MSG_ATTR(cb->extack, snapshot_attr, "requested snapshot does not exist");
+			err = -EINVAL;
+			goto out_unlock;
+		}
+		region_cb = &devlink_region_snapshot_fill;
+		region_cb_priv = snapshot;
 	}
 
 	if (attrs[DEVLINK_ATTR_REGION_CHUNK_ADDR] &&
@@ -6633,9 +6665,9 @@ static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
 		goto nla_put_failure;
 	}
 
-	err = devlink_nl_region_read_fill(skb, &devlink_region_snapshot_fill,
-					  snapshot, start_offset, end_offset,
-					  &ret_offset, cb->extack);
+	err = devlink_nl_region_read_fill(skb, region_cb, region_cb_priv,
+					  start_offset, end_offset, &ret_offset,
+					  cb->extack);
 
 	if (err && err != -EMSGSIZE)
 		goto nla_put_failure;
-- 
2.38.1.420.g319605f8f00e

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