Hi Jianfeng,

-----Original Message-----
From: Tan, Jianfeng
Sent: Monday, January 11, 2016 7:39 AM
To: Ananyev, Konstantin; Nélio Laranjeiro; dev@dpdk.org
Subject: Re: [dpdk-dev] [PATCH 01/12] ethdev: add API to query what/if packet type is set

Hi,

According to the proposal, I'm going to fix the definition of this API
as below:
/**
  * Retrieve the contextual information of an Ethernet device.
  *
  * @param port_id
  *   The port identifier of the Ethernet device.
  * @param ptype_mask
  *   A hint of what kind of packet type which the caller is interested in
  * @param ptypes
  *   An array of packet types to be filled with
  * @param num
  * Size of ptypes[]
  * @return
  *   - (>=0) if successful. Indicate number of valid values in ptypes
array.
  *   - (-ENOTSUP) if hardware-assisted VLAN stripping not configured.
  *   - (-ENODEV) if *port_id* invalid.
  */
extern int rte_eth_dev_get_ptype_info(uint8_t port_id,
                                 uint32_t ptype_mask, uint32_t ptypes[],
uint32_t num);

Unresolved issues:
1) When num is exceeded, we just stop there and return num, or return
-ENOMEM?

I think when num is exceeded it should return number of entries enough to
return all requested packet types.
Same as snprintf() does when it has to truncate the output buffer.

The first way has a bug when: what app is exactly asking for is not
filled in ptypes[] because of
exceeding num, but app believes this API returns with success.

It is a caller responsibility to check the return value and handle it properly.
When return value  exceeds num - caller can  resize ptypes[] and call get_ptype_info() again.

2) if RTE_PTYPE_*_MAX_NUM macros necessary? Without them, we could calculate
num through 2^(number of bit 1 in RTE_PTPE_*_MASK).

I don't think caller has to guess somehow what number of entries in ptypes[] he need .
He can retrieve that information from get_ptype_info() itself.
Something like that for example:

num = rte_eth_dev_get_ptype_info(port, UINT32_MAX, NULL, 0);
if (num < 0) return num;
ptypes = alloca(num * sizeof(ptypes[0]);
ret = rte_eth_dev_get_ptype_info(port, UINT32_MAX, ptypes, num);
if (ret != num) return -1;
....

Konstantin

Thanks,
Jianfeng