[v20.11,2/2] eal: improve device probing API

  This patch makes rte_dev_probe() to return the
rte_device pointer on success and NULL on error
instead of returning 0 on success and negative
value on error.

The goal is to avoid that the calling application
iterates the devices list afterwards to retrieve
the pointer. Retrieving the pointer is required
for calling rte_dev_remove() later.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
---
 app/test-pmd/testpmd.c                 |  2 +-
 drivers/net/failsafe/failsafe.c        |  5 +++--
 lib/librte_eal/common/eal_common_dev.c | 18 ++++++++++--------
 lib/librte_eal/include/rte_dev.h       |  4 ++--
 4 files changed, 16 insertions(+), 13 deletions(-)
  

Hello Maxime,

On 08/06/20 17:53 +0200, Maxime Coquelin wrote:
> This patch makes rte_dev_probe() to return the
> rte_device pointer on success and NULL on error
> instead of returning 0 on success and negative
> value on error.
> 
> The goal is to avoid that the calling application
> iterates the devices list afterwards to retrieve
> the pointer. Retrieving the pointer is required
> for calling rte_dev_remove() later.
> 

I agree with the idea. I recall starting to do it on the legacy functions
(rte_eal_hotplug_*), but it was scrapped for API compat.

> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> ---
>  app/test-pmd/testpmd.c                 |  2 +-
>  drivers/net/failsafe/failsafe.c        |  5 +++--
>  lib/librte_eal/common/eal_common_dev.c | 18 ++++++++++--------
>  lib/librte_eal/include/rte_dev.h       |  4 ++--
>  4 files changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/app/test-pmd/testpmd.c b/app/test-pmd/testpmd.c
> index 4989d22ca8..f777f449a8 100644
> --- a/app/test-pmd/testpmd.c
> +++ b/app/test-pmd/testpmd.c
> @@ -2764,7 +2764,7 @@ attach_port(char *identifier)
>  		return;
>  	}
>  
> -	if (rte_dev_probe(identifier) < 0) {
> +	if (rte_dev_probe(identifier) == NULL) {
>  		TESTPMD_LOG(ERR, "Failed to attach port %s\n", identifier);
>  		return;
>  	}
> diff --git a/drivers/net/failsafe/failsafe.c b/drivers/net/failsafe/failsafe.c
> index 72362f35de..e32effdef2 100644
> --- a/drivers/net/failsafe/failsafe.c
> +++ b/drivers/net/failsafe/failsafe.c
> @@ -341,6 +341,7 @@ rte_pmd_failsafe_probe(struct rte_vdev_device *vdev)
>  	struct rte_eth_dev *eth_dev;
>  	struct sub_device  *sdev;
>  	struct rte_devargs devargs;
> +	struct rte_device *dev;
>  	uint8_t i;
>  	int ret;
>  
> @@ -378,8 +379,8 @@ rte_pmd_failsafe_probe(struct rte_vdev_device *vdev)
>  				continue;
>  			}
>  			if (!devargs_already_listed(&devargs)) {
> -				ret = rte_dev_probe(devargs.name);
> -				if (ret < 0) {
> +				dev = rte_dev_probe(devargs.name);
> +				if (dev == NULL) {
>  					ERROR("Failed to probe devargs %s",
>  					      devargs.name);
>  					continue;
> diff --git a/lib/librte_eal/common/eal_common_dev.c b/lib/librte_eal/common/eal_common_dev.c
> index 9e4f09d83e..72baae2e48 100644
> --- a/lib/librte_eal/common/eal_common_dev.c
> +++ b/lib/librte_eal/common/eal_common_dev.c
> @@ -120,7 +120,9 @@ rte_eal_hotplug_add(const char *busname, const char *devname,
>  	if (ret != 0)
>  		return ret;
>  
> -	ret = rte_dev_probe(devargs);
> +	if (rte_dev_probe(devargs) == NULL)
> +		ret = -1;
> +
>  	free(devargs);
>  
>  	return ret;
> @@ -192,7 +194,7 @@ local_dev_probe(const char *devargs, struct rte_device **new_dev)
>  	return ret;
>  }
>  
> -int
> +struct rte_device *
>  rte_dev_probe(const char *devargs)
>  {
>  	struct eal_dev_mp_req req;
> @@ -212,12 +214,12 @@ rte_dev_probe(const char *devargs)
>  		if (ret != 0) {
>  			RTE_LOG(ERR, EAL,
>  				"Failed to send hotplug request to primary\n");
> -			return -ENOMSG;
> +			return NULL;

Is is a problem to keep the ENOMSG through rte_errno?

>  		}
>  		if (req.result != 0)
>  			RTE_LOG(ERR, EAL,
>  				"Failed to hotplug add device\n");
> -		return req.result;
> +		return NULL;
>  	}
>  
>  	/* attach a shared device from primary start from here: */
> @@ -236,7 +238,7 @@ rte_dev_probe(const char *devargs)
>  		 * process.
>  		 */
>  		if (ret != -EEXIST)
> -			return ret;
> +			return dev;
>  	}
>  
>  	/* primary send attach sync request to secondary. */
> @@ -261,11 +263,11 @@ rte_dev_probe(const char *devargs)
>  
>  		/* for -EEXIST, we don't need to rollback. */
>  		if (ret == -EEXIST)
> -			return ret;
> +			return dev;
>  		goto rollback;
>  	}
>  
> -	return 0;
> +	return dev;
>  
>  rollback:
>  	req.t = EAL_DEV_REQ_TYPE_ATTACH_ROLLBACK;
> @@ -282,7 +284,7 @@ rte_dev_probe(const char *devargs)
>  			"Failed to rollback device attach on primary."
>  			"Devices in secondary may not sync with primary\n");
>  
> -	return ret;
> +	return NULL;
>  }
>  
>  int
> diff --git a/lib/librte_eal/include/rte_dev.h b/lib/librte_eal/include/rte_dev.h
> index c8d985fb5c..9cf7c7fd71 100644
> --- a/lib/librte_eal/include/rte_dev.h
> +++ b/lib/librte_eal/include/rte_dev.h
> @@ -148,9 +148,9 @@ int rte_eal_hotplug_add(const char *busname, const char *devname,
>   * @param devargs
>   *   Device arguments including bus, class and driver properties.
>   * @return
> - *   0 on success, negative on error.
> + *   Generic device pointer on success, NULL on error.

If rte_errno is set, mapping codes to meanings would be helpful here.

Acked-by: Gaetan Rivet <grive@u256.net>
  

Hi Gaëtan,

On 6/10/20 2:06 PM, Gaëtan Rivet wrote:
> Hello Maxime,
> 
> On 08/06/20 17:53 +0200, Maxime Coquelin wrote:
>> This patch makes rte_dev_probe() to return the
>> rte_device pointer on success and NULL on error
>> instead of returning 0 on success and negative
>> value on error.
>>
>> The goal is to avoid that the calling application
>> iterates the devices list afterwards to retrieve
>> the pointer. Retrieving the pointer is required
>> for calling rte_dev_remove() later.
>>
> 
> I agree with the idea. I recall starting to do it on the legacy functions
> (rte_eal_hotplug_*), but it was scrapped for API compat.
> 
>> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
>> ---
>>  app/test-pmd/testpmd.c                 |  2 +-
>>  drivers/net/failsafe/failsafe.c        |  5 +++--
>>  lib/librte_eal/common/eal_common_dev.c | 18 ++++++++++--------
>>  lib/librte_eal/include/rte_dev.h       |  4 ++--
>>  4 files changed, 16 insertions(+), 13 deletions(-)
>>
...
>>  
>>  int
>> diff --git a/lib/librte_eal/include/rte_dev.h b/lib/librte_eal/include/rte_dev.h
>> index c8d985fb5c..9cf7c7fd71 100644
>> --- a/lib/librte_eal/include/rte_dev.h
>> +++ b/lib/librte_eal/include/rte_dev.h
>> @@ -148,9 +148,9 @@ int rte_eal_hotplug_add(const char *busname, const char *devname,
>>   * @param devargs
>>   *   Device arguments including bus, class and driver properties.
>>   * @return
>> - *   0 on success, negative on error.
>> + *   Generic device pointer on success, NULL on error.
> 
> If rte_errno is set, mapping codes to meanings would be helpful here.

Actually David made me the same comment before I post the patch.
I am fine with setting rte_errno. If we do that, I think we should have
fixed error code in rte_dev_probe() and not propagate error codes from
functions it calls. Otherwise it's likely the API doc will be outdated
quite rapidly.

What do you think?

> Acked-by: Gaetan Rivet <grive@u256.net>
> 

Great, could you also ack the deprecation notice, as this is the part
that needs to be merged into v20.08?

Thanks!
Maxime
  

On 10/06/20 19:08 +0200, Maxime Coquelin wrote:
> Hi Gaëtan,
> 
> On 6/10/20 2:06 PM, Gaëtan Rivet wrote:
> > Hello Maxime,
> > 
> > On 08/06/20 17:53 +0200, Maxime Coquelin wrote:
> >> This patch makes rte_dev_probe() to return the
> >> rte_device pointer on success and NULL on error
> >> instead of returning 0 on success and negative
> >> value on error.
> >>
> >> The goal is to avoid that the calling application
> >> iterates the devices list afterwards to retrieve
> >> the pointer. Retrieving the pointer is required
> >> for calling rte_dev_remove() later.
> >>
> > 
> > I agree with the idea. I recall starting to do it on the legacy functions
> > (rte_eal_hotplug_*), but it was scrapped for API compat.
> > 
> >> Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
> >> ---
> >>  app/test-pmd/testpmd.c                 |  2 +-
> >>  drivers/net/failsafe/failsafe.c        |  5 +++--
> >>  lib/librte_eal/common/eal_common_dev.c | 18 ++++++++++--------
> >>  lib/librte_eal/include/rte_dev.h       |  4 ++--
> >>  4 files changed, 16 insertions(+), 13 deletions(-)
> >>
> ...
> >>  
> >>  int
> >> diff --git a/lib/librte_eal/include/rte_dev.h b/lib/librte_eal/include/rte_dev.h
> >> index c8d985fb5c..9cf7c7fd71 100644
> >> --- a/lib/librte_eal/include/rte_dev.h
> >> +++ b/lib/librte_eal/include/rte_dev.h
> >> @@ -148,9 +148,9 @@ int rte_eal_hotplug_add(const char *busname, const char *devname,
> >>   * @param devargs
> >>   *   Device arguments including bus, class and driver properties.
> >>   * @return
> >> - *   0 on success, negative on error.
> >> + *   Generic device pointer on success, NULL on error.
> > 
> > If rte_errno is set, mapping codes to meanings would be helpful here.
> 
> Actually David made me the same comment before I post the patch.
> I am fine with setting rte_errno. If we do that, I think we should have
> fixed error code in rte_dev_probe() and not propagate error codes from
> functions it calls. Otherwise it's likely the API doc will be outdated
> quite rapidly.
> 
> What do you think?
> 

Well we're stuck with the classic errno limitations.

I agree with you, if we consider possible errors as part of a function
API, then we cannot recursively inherit this API from callees.

That being said, masking errors is not ok. If an error cannot be handled
by rte_dev_probe(), it should log an appropriate message and set
rte_errno to a value that is part of its API. If the error can be
handled, then errno should be reset to its original value preceding
rte_dev_probe() call.

Of course the EAL rarely does it, and even myself I probably rarely
respected this behavior, but it would be nice if we could all define a
common agreed-upon discipline in the EAL and stick to it. I think the
current state of error reporting in EAL is terrible for users downstream.

> > Acked-by: Gaetan Rivet <grive@u256.net>
> > 
> 
> Great, could you also ack the deprecation notice, as this is the part
> that needs to be merged into v20.08?
> 

I wanted to refresh myself with the latest rules about API breakage
before doing so but got context switched away :) . I will get back to it.

> Thanks!
> Maxime
>