From af6397c9ee2b42988c912dcad2fca1f43d5c1c99 Mon Sep 17 00:00:00 2001 From: Jacob Keller Date: Mon, 28 Nov 2022 12:36:44 -0800 Subject: 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 requested via the new DEVLINK_ATTR_REGION_DIRECT. If this attribute is set, then perform a direct read instead of using a snapshot. Direct read is mutually exclusive with DEVLINK_ATTR_REGION_SNAPSHOT_ID, and care is taken to ensure that we reject commands which provide incorrect attributes. Regions must enable support for direct read by implementing the .read() callback function. If a region does not support such direct reads, a suitable extended error message is reported. Signed-off-by: Jacob Keller Reviewed-by: Jiri Pirko Signed-off-by: Jakub Kicinski --- Documentation/networking/devlink/devlink-region.rst | 13 +++++++++++++ 1 file changed, 13 insertions(+) (limited to 'Documentation/networking') diff --git a/Documentation/networking/devlink/devlink-region.rst b/Documentation/networking/devlink/devlink-region.rst index f06dca9a1eb6..9232cd7da301 100644 --- a/Documentation/networking/devlink/devlink-region.rst +++ b/Documentation/networking/devlink/devlink-region.rst @@ -31,6 +31,15 @@ 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. User space can request a direct read by using the +``DEVLINK_ATTR_REGION_DIRECT`` attribute instead of specifying a snapshot +id. + example usage ------------- @@ -65,6 +74,10 @@ 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. -- cgit v1.2.3