netdev - Re: [PATCH 13/15] devlink: support directly reading from region memory

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Message-ID: <20200131100744.61ec7632@cakuba.hsd1.ca.comcast.net>
Date:   Fri, 31 Jan 2020 10:07:44 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Jacob Keller <jacob.e.keller@...el.com>
Cc:     netdev@...r.kernel.org, jiri@...nulli.us, valex@...lanox.com,
        linyunsheng@...wei.com, lihong.yang@...el.com
Subject: Re: [PATCH 13/15] devlink: support directly reading from region
 memory

On Thu, 30 Jan 2020 14:59:08 -0800, Jacob Keller wrote:
> Add a new region operation for directly reading from a region, without
> taking a full snapshot.
> 
> Extend the DEVLINK_CMD_REGION_READ to allow directly reading from
> a region, if supported. Instead of reporting a missing snapshot id as
> invalid, check to see if direct reading is implemented for the region.
> If so, use the direct read operation to grab the current contents of the
> region.
> 
> This new behavior of DEVLINK_CMD_REGION_READ should be backwards
> compatible. Previously, all kernels rejected such
> a DEVLINK_CMD_REGION_READ with -EINVAL, and will now either accept the
> call or report -EOPNOTSUPP for regions which do not implement direct
> access.
> 
> Signed-off-by: Jacob Keller <jacob.e.keller@...el.com>

> +static int devlink_nl_region_read_direct_fill(struct sk_buff *skb,
> +					      struct devlink *devlink,
> +					      struct devlink_region *region,
> +					      struct nlattr **attrs,
> +					      u64 start_offset,
> +					      u64 end_offset,
> +					      bool dump,
> +					      u64 *new_offset)
> +{
> +	u64 curr_offset = start_offset;
> +	int err = 0;
> +	u8 *data;
> +
> +	/* Allocate and re-use a single buffer */
> +	data = kzalloc(DEVLINK_REGION_READ_CHUNK_SIZE, GFP_KERNEL);
> +	if (!data)
> +		return -ENOMEM;
> +
> +	*new_offset = start_offset;
> +
> +	if (end_offset > region->size || dump)
> +		end_offset = region->size;
> +
> +	while (curr_offset < end_offset) {
> +		u32 data_size;
> +
> +		if (end_offset - curr_offset < DEVLINK_REGION_READ_CHUNK_SIZE)
> +			data_size = end_offset - curr_offset;
> +		else
> +			data_size = DEVLINK_REGION_READ_CHUNK_SIZE;

Also known as min() ?

> +		err = region->ops->read(devlink, curr_offset, data_size, data);
> +		if (err)
> +			break;
> +
> +		err = devlink_nl_cmd_region_read_chunk_fill(skb, devlink,
> +							    data, data_size,
> +							    curr_offset);
> +		if (err)
> +			break;
> +
> +		curr_offset += data_size;
> +	}
> +	*new_offset = curr_offset;
> +
> +	kfree(data);
> +
> +	return err;
> +}
> +
>  static int devlink_nl_cmd_region_read_dumpit(struct sk_buff *skb,
>  					     struct netlink_callback *cb)
>  {

> +	/* Region may not support direct read access */
> +	if (direct && !region->ops->read) {

for missing trigger you added an extack, perhaps makes sense here, too?

> +		err = -EOPNOTSUPP;
> +		goto out_unlock;
> +	}
> +
>  	hdr = genlmsg_put(skb, NETLINK_CB(cb->skb).portid, cb->nlh->nlmsg_seq,
>  			  &devlink_nl_family, NLM_F_ACK | NLM_F_MULTI,
>  			  DEVLINK_CMD_REGION_READ);

Generally all the devlink parts look quite reasonable to me 👍