[dpdk-dev] [PATCHv4 4/5] dpdk: add __experimental tag to appropriate api calls

Neil Horman nhorman at tuxdriver.com
Thu Jan 11 22:24:05 CET 2018


On Thu, Jan 11, 2018 at 08:06:33PM +0000, Ferruh Yigit wrote:
> On 12/13/2017 3:17 PM, Neil Horman wrote:
> > Append the __experimental tag to api calls appearing in the EXPERIMENTAL
> > section of their libraries version map
> > 
> > Signed-off-by: Neil Horman <nhorman at tuxdriver.com>
> > CC: Thomas Monjalon <thomas at monjalon.net>
> > CC: "Mcnamara, John" <john.mcnamara at intel.com>
> > CC: Bruce Richardson <bruce.richardson at intel.com>
> > ---
> >  lib/librte_eal/common/eal_common_dev.c             |  6 ++-
> >  lib/librte_eal/common/eal_common_devargs.c         |  7 +--
> >  lib/librte_eal/common/include/rte_dev.h            |  6 ++-
> >  lib/librte_eal/common/include/rte_devargs.h        |  8 ++--
> >  lib/librte_eal/common/include/rte_service.h        | 47 ++++++++++---------
> >  .../common/include/rte_service_component.h         | 14 +++---
> >  lib/librte_eal/common/rte_service.c                | 52 ++++++++++++----------
> >  lib/librte_eal/linuxapp/eal/eal.c                  |  1 +
> >  lib/librte_ether/rte_mtr.c                         | 25 ++++++-----
> >  lib/librte_ether/rte_mtr.h                         | 26 +++++------
> >  lib/librte_flow_classify/rte_flow_classify.c       | 13 +++---
> >  lib/librte_flow_classify/rte_flow_classify.h       | 11 ++---
> >  lib/librte_security/rte_security.c                 | 16 +++----
> >  lib/librte_security/rte_security.h                 | 23 +++++-----
> 
> It may not be the responsibility of this patchset, but there are more
> experimental APIs in DPDK.
> 
Thats an interesting statement to make.  This patchset creates a build time
check that compares symbols located in the EXPERIMENTAL version section of a
libraries' version map file to the symbols that are marked with this new tag,
throwing an error if they don't match.  I believe what you say in that there may
be additional APIs that are experimental, but given that, I would have to
conclude one of the following:

1) The missing API's are macros or static inline functions that are not exported
from libraries directly

2) The documentation for experimental API's are out of sync, in that they have
legitimately moved to be supported API's and the documentation needs to be
updated

3) There are API's which are experimental that have been incorrectly placed in a
versioned tag.

I made a pretty good effort to scan comments for the word EXPERIMENTAL so that I
could catch item (1).  And while I may not have caught them all, I'd like to
think I got a good chunk of them.  That leaves cleanup of (2) and (3), which I
think this patchset can help us idenfity.

> Using EXPERIMENTAL tag in linker script is relatively new approach and this was
> not a requirement, so many experimental APIs are documented in API documentation
> (header file doxygen comment).
> Sample: librte_member
> 
That sounds like case (3) above.

Thats a bit odd.  I understand that the use of the EXPERIMENTAL version tag is
new, but once it was introduced it should have been made a requirement.  There
would have been no penalty for moving the version number (as doing so would not
have violated ABI guarantees, given that those API's were appropriately
documented as experimental).  If they have not been, then the use of the
EXPERIMENTAL tag isn't overly useful, as it doesn't provide any segregation of
the stable ABI from the unstable ABI.

> It is required to scan all header files and update their linker scripts for the
> experimental APIs.
> 
Yes and no.  If a given library is not marked as experimental in its version
map, this change won't flag it as a problem, but if its intended to be
experimental (i.e. if its likely to have its ABI fluctuate), then yes, we should
take the appropriate steps to flag it as such properly.

If a given library is intended to be experimental, I would say yes,
the author should make the appropriate chage to the version map, and then the
corresponding change to the headers  and c files with this new tag.
Alternatively, they might choose to simply update the documentation to reflect
the fact that the ABI for that library is now stable.

The thing that should definately not hapen though, is a half measure.  We
shouldn't allow libraries to call themselves experimental, and then excuse them
from any rules we have regarding their in-code representation.  If we have an
EXPERIMENTAL version in the map, we should require its use, and by extension
require this tag when its merged for the reasons previously outlined

Neil


> >  14 files changed, 139 insertions(+), 116 deletions(-)
> 
> <...>
> 
> 


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