[dpdk-dev] Question: typedef of eventdev_info_get_t bug?

Van Haaren, Harry harry.van.haaren at intel.com
Mon Feb 1 10:44:09 CET 2021

> -----Original Message-----
> From: dev <dev-bounces at dpdk.org> On Behalf Of Fredrik A Lindgren
> Sent: Monday, February 1, 2021 9:22 AM
> To: dev at dpdk.org
> Subject: [dpdk-dev] Question: typedef of eventdev_info_get_t bug?
> While debugging a driver I was looking at the code and realized that
> eventdev_info_get_t typedef is defined with void return value but documentation
> for it says it should return 0

Hi Fredrik,

Be aware that your snippets of code below is mixing Event-dev and Eth-dev.
This is likely the cause of confusion.

> lib/librte_eventdev/eventdev_pmd.h:
> ...
> * @return
> *   Returns 0 on success
> */
> typedef void (*eventdev_info_get_t)(struct rte_eventdev *dev,
>                                                           struct rte_event_dev_info *dev_info);
> ...
> struct rte_eventdev_ops {
>                              eventdev_info_get_t dev_infos_get;              /**< Get device info. */
> ...
> While return value from it is used in lib/librte_ethdev/rte_ethdev.c:
> int
> rte_eth_dev_info_get(uint16_t port_id, struct rte_eth_dev_info *dev_info)
> ...
>    diag = (*dev->dev_ops->dev_infos_get)(dev, dev_info);
>    if (diag != 0) {
> ...

At the Eventdev layer, info_get() can return int (particularly 0 on success, or -ERROR values).
At the Eventdev PMD layer, info_get() has a return void (the PMD cannot indicate failure on providing its info)

Hence, the info_get() typedef (for the PMD) is void, but the Eventdev layer itself checks some dev_id values
etc, and can return -EINVAL or -ENOTSUP in case the PMD doesn't support info_get().

> Driver I'm debugging doesn't have any return statement in it's dev_infos_get
> function which seems to cause it to have "result" of last operation done in that
> function as return value.
> Though this behavior may be compiler specific but it should probably be clarified and
> updated (change prototype of stop using return value) to avoid issue with it.

Perhaps provide some more detail on Eventdev/Ethdev that you're debugging a driver on,
provide some links to specific parts of the code? It seems like (from Eventdev anyway) its
meant to work this way.

> Br,
> Fredrik

Regards, -Harry

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