On Fri, May 20, 2016 at 10:30:27AM +0300, Panu Matilainen wrote:

On 05/19/2016 04:26 PM, Neil Horman wrote:

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On Thu, May 19, 2016 at 09:08:52AM +0300, Panu Matilainen wrote:

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On 05/18/2016 04:48 PM, Neil Horman wrote:

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On Wed, May 18, 2016 at 03:48:12PM +0300, Panu Matilainen wrote:

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On 05/18/2016 03:03 PM, Neil Horman wrote:

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On Wed, May 18, 2016 at 02:48:30PM +0300, Panu Matilainen wrote:

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On 05/16/2016 11:41 PM, Neil Horman wrote:

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This tool searches for the primer sting PMD_DRIVER_INFO= in any ELF binary,
and, if found parses the remainder of the string as a json encoded string,
outputting the results in either a human readable or raw, script parseable
format

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Bruce Richardson <redacted>
CC: Thomas Monjalon <redacted>
CC: Stephen Hemminger <stephen@networkplumber.org>
CC: Panu Matilainen <redacted>
---
 tools/pmd_hw_support.py | 174 ++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 174 insertions(+)
 create mode 100755 tools/pmd_hw_support.py

diff --git a/tools/pmd_hw_support.py b/tools/pmd_hw_support.py
new file mode 100755
index 0000000..0669aca
--- /dev/null
+++ b/tools/pmd_hw_support.py

@@ -0,0 +1,174 @@
+#!/usr/bin/python3

I think this should use /usr/bin/python to be consistent with the other
python scripts, and like the others work with python 2 and 3. I only tested
it with python2 after changing this and it seemed to work fine so the
compatibility side should be fine as-is.

Sure, I can change the python executable, that makes sense.

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On the whole, AFAICT the patch series does what it promises, and works for
both static and shared linkage. Using JSON formatted strings in an ELF
section is a sound working technical solution for the storage of the data.
But the difference between the two cases makes me wonder about this all...

You mean the difference between checking static binaries and dynamic binaries?
yes, there is some functional difference there

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For static library build, you'd query the application executable, eg

Correct.

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testpmd, to get the data out. For a shared library build, that method gives
absolutely nothing because the data is scattered around in individual
libraries which might be just about wherever, and you need to somehow

Correct, I figured that users would be smart enough to realize that with
dynamically linked executables, they would need to look at DSO's, but I agree,
its a glaring diffrence.

Being able to look at DSOs is good, but expecting the user to figure out
which DSOs might be loaded and not and where to look is going to be well
above many users. At very least it's not what I would call user-friendly.

I disagree, there is no linkage between an application and the dso's it opens
via dlopen that is exportable.  The only way to handle that is to have a
standard search path for the pmd_hw_info python script.  Thats just like modinfo
works (i.e. "modinfo bnx2" finds the bnx2 module for the running kernel).  We
can of course do something simmilar, but we have no existing implicit path
information to draw from to do that (because you can have multiple dpdk installs
side by side).  The only way around that is to explicitly call out the path on
the command line.

There's no telling what libraries user might load at runtime with -D, that
is true for both static and shared libraries.

I agree.

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When CONFIG_RTE_EAL_PMD_PATH is set, as it is likely to be on distro builds,
you *know* that everything in that path will be loaded on runtime regardless
of what commandline options there might be so the situation is actually on
par with static builds. Of course you still dont know about ones added with
-D but that's a limitation of any solution that works without actually
running the app.

Its not on ours, as the pmd libraries get placed in the same directory as every
other dpdk library, and no one wants to try (and fail to load
rte_sched/rte_acl/etc twice, or deal with the fallout of trying to do so, or
adjust the packaging so that pmds are placed in their own subdirectory, or
handle the need for multiuser support.

Err. I suggest you actually look at the package.

Oh, you're right, you did make a change to set it.  I never saw a bugzilla for
that.  Sorry.

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Using CONFIG_RTE_EAL_PMD_PATH also doesn't account for directory changes.  This
use case:
1) run pmdinfo <app>
2) remove DSOs from RTE_EAL_PMD_PATH
3) execute <app>

leads to erroneous results, as hardware support that was reported in (1) is no
longer available at (3)

Yes, and in place of 2) you could also add DSOs there since you found
something missing. Just like updating statically <app> at 2) could change
it. RTE_EAL_PMD_PATH is not expected to point to /tmp like location where
stuff randomly appears and disappears.

So....for this hypothetical admin that we're speaking of, you expect them to be
smart enough to understand that adding additional hardware support requires them
to build an extra DSO, and place it (or a symlink to it) in a distro determined
directory, but then not have the wherewithal to understand that querying
hardware support require that you query that specific binary, rather than
assuming the tool will automagically attempt to glean that path from the core
set of libraries?

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It also completely misses any libraries that we load via the -d option on the
command line, which won't be included in RTE_EAL_PMD_PATH, so following that
path is a half measure at best, and I think that leads to erroneous results.

This same problem with -d exists for statically linked apps, as you actually
agreed earlier in your email. So that's hardly an argument here.

Yes, I did agree, but you're twisting my argument.  I'm not arguing that I have
some other solution for this problem, I'm saying that, as a matter of
consistency, for libraries that offer hardware support which are loaded at run
time (which applies equally to those found in RTE_EAL_PMD_PATH, and those loaded
via -d), that we should not automatically report on those libraries, because we
don't know until run time if they will be available.  For both of these cases we
should only report on hardware support if the user queries those binary DSO's
directly.  I don't care if the application automatically loads from that
directory or not, until run time, we don't know what the contents of that
directory will be, and so we aren't guaranteed that the output of pmdinfo, if it
automatically searches that path, will be accurate.

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discover the location + correct library files to be able to query that. For
the shared case, perhaps the script could be taught to walk files in
CONFIG_RTE_EAL_PMD_PATH to give in-the-ballpark correct/identical results

My initial thought would be to run ldd on the executable, and use a heuristic to
determine relevant pmd DSO's, and then feed each of those through the python
script.  I didn't want to go to that trouble unless there was consensus on it
though.

Problem is, ldd doesn't know about them either because the pmds are not
linked to the executables at all anymore. They could be force-linked of
course, but that means giving up the flexibility of plugins, which IMO is a
no-go. Except maybe as an option, but then that would be a third case to
support.

Thats not true at all, or at least its a perfectly valid way to link the DSO's
in at link time via -lrte_pmd_<driver>.  Its really just the dlopen case we need
to worry about.  I would argue that, if they're not explicitly linked in like
that, then its correct to indicate that an application supports no hardware,
because it actually doesn't, it only supports the pmds that it chooses to list
on the command line.  And if a user is savy enough to specify a pmd on the
application command line, then they are perfectly capable of specifying the same
path to the hw_info script.

Yes you can force-link apps to every driver on existence, but it requires
not just linking but using --whole-archive.

For the static case, yes, and thats what DPDK does, and likely will in
perpituity, unless there is a major architectural change in the project (see
commit 20afd76a504155e947c770783ef5023e87136ad8).

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The apps in DPDK itself dont in
shared link setup (take a look at testpmd) and I think its for a damn good
reason - the drivers are plugins and that's how plugins are expected to
work: they are not linked to, they reside in a specific path which is

I know, I'm the one that made that change when we introduced the
PMD_REGISTER_DRIVER macro :).  That doesn't mean its not a valid case when
building apps, and one that we can take advantage of opportunistically.  There
are three cases we have to handle:

1) Static linking - This is taken care of
2) Dynamic linking via DT_NEEDED entries - this is taken care of
3) Dynamic linking via dlopen - This is what we're discussing here

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scanned at runtime and plugins loaded to provide extra functionality.

Its the runtime part that makes this non-functional.  Just because you scan
all the DSO's in the RTE_EAL_PATH, doesn't mean they will be there when the app
is run, nor does it mean you will get a comprehensive list of hardware support,
because it doesn't include additional paths/DSO's added via -d.  I would much
rather have users understand that an app has _no_ hardware support if it uses
DSO's, because the hardware support is included with the DSO's themself, not the
application (saving for the DT_NEEDED case above, where application execution is
predicated on the availability of those shared objects)

I'm not going to repeat all the earlier arguments from above, but -d is
different because its specified by the user at runtime.

So are the contents of the directory pointed to by RTE_EAL_PMD_PATH.

RTE_EAL_PMD_PATH is built into the EAL library and you can't disable it at
runtime. So an app linked to EAL with RTE_EAL_PMD_PATH configured is
guaranteed to load everything from that path, regardless of what the user
specifies at the runtime. I agree it is somewhat different from the static
case because its, well, dynamic, by design. Note that I fully agree there is
value in being able to query *just* the binary and no magic lookups, because
for some uses you want just that so it'd need to be possible to disable such
lookup in the tool.

Anyway, unless something really new turns up in this discussion I'm going to
shut up now since I would hope I've made my opinion and point clear by now.

Yes, you've made yourself very clear, and I hope I've done the same.  We're just
not going to agree on this.

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when querying the executable as with static builds. If identical operation
between static and shared versions is a requirement (without running the app
in question) then query through the executable itself is practically the
only option. Unless some kind of (auto-generated) external config file
system ala kernel depmod / modules.dep etc is brought into the picture.

Yeah, I'm really trying to avoid that, as I think its really not a typical part
of how user space libraries are interacted with.

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For shared library configurations, having the data in the individual pmds is
valuable as one could for example have rpm autogenerate provides from the
data to ease/automate installation (in case of split packaging and/or 3rd
party drivers). And no doubt other interesting possibilities. With static
builds that kind of thing is not possible.

Right.

Note, this also leaves out PMD's that are loaded dynamically (i.e. via dlopen).
For those situations I don't think we have any way of 'knowing' that the
application intends to use them.

Hence my comment about CONFIG_RTE_EAL_PMD_PATH above, it at least provides a
reasonable heuristic of what would be loaded by the app when run. But
ultimately the only way to know what hardware is supported at a given time
is to run an app which calls rte_eal_init() to load all the drivers that are
present and work from there, because besides CONFIG_RTE_EAL_PMD_PATH this
can be affected by runtime commandline switches and applies to both shared
and static builds.

I'm not sure I agree with that.  Its clearly tempting to use, but its not
at all guaranteed to be accurate (the default is just set to "", and there is no
promise anyone will set it properly).

The promise is that shared builds are barely functional unless its set
correctly, because zero drivers are linked to testpmd in shared config. So
you're kinda likely to notice if its not set.

You're twisting the meaning of 'barely functional' here.  I agree that shared
builds are barely functional, because they have no self-contained hardware
support, and as such, running pmdinfo.py on such an application should report
exactly that.

That said, in order to run, and DPDK application built to use shared libraries
has to use one of two methods to obtain hardware support

A) direct shared linking (the DT_NEEDED case) - This case is handled, and we
report hardware support when found, as the application won't run unless those
libraries are resolved

b) dynamic loading via dlopen - This case shouldn't be handled, because the
application in reality doesn't support  any hardware.  Hardware support is
garnered at run time when the EAL_PMD_PATH (and any other paths added via the -d
option) are scanned.  In this case, pmdinfo shouldn't report any hardware
support, it should only do so if the pmd DSO is queried directly.

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It defaults to empty because at the time there was no standard installation
available at that time. Setting a reasonable default is tricky still because
it needs to be set before build whereas install path is set at install time.

Exactly, which is why distros don't use it.  It also neglects the multiuser case
(in which different users may want to load different hardware support).

Ehh? It exists *primarily* for distro needs. I suggest you take a look how
it all works in current Fedora and RHEL packages. The packaging is
monolithic at the moment but thanks to the plugin autoloading, it would be
possible to split drivers into different subpackages to eg provide minimal
driver package for use in virtual guests where all space counts etc, and to
allow 3rd party drivers to be dropped in and so on.

And if you run pmdinfo, then remove a package that provides a 3rd party driver
which it previously reported support for?

The bottom line is, the application you scan with pmdinfo doesn't acutally
support any hardware (save for whats statically linked or dynamically linked via
DT_NEEDED entries).  It has no support for any hardware provided by the plugin
interface until run time when those directories are queried and loaded.  As such
the only sane consistent thing to do is not report on that hardware support.

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And it also requires that the binary will
be tied to a specific release.  I really think that, given the fact that
distributions generally try to package dpdk in such a way that multiple dpdk
versions might be available, the right solution is to just require a full path
specification if you want to get hw info for a DSO that is dynamically loaded
via dlopen from the command line.  Otherwise you're going to fall into this trap
where you might be looking implicitly at an older version of the PMD while your
application may use a newer version.

If there are multiple dpdk versions available then they just need to have
separate PMD paths, but that's not a problem.

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Calling up on the list of requirements from
http://dpdk.org/ml/archives/dev/2016-May/038324.html, I see a pile of
technical requirements but perhaps we should stop for a moment to think
about the use-cases first?

To ennumerate the list:

- query all drivers in static binary or shared library (works)
- stripping resiliency (works)
- human friendly (works)
- script friendly (works)
- show driver name (works)
- list supported device id / name (works)
- list driver options (not yet, but possible)
- show driver version if available (nope, but possible)
- show dpdk version (nope, but possible)
- show kernel dependencies (vfio/uio_pci_generic/etc) (nope)
- room for extra information? (works)

Of the items that are missing, I've already got a V2 started that can do driver
options, and is easier to expand.  Adding in the the DPDK and PMD version should
be easy (though I think they can be left out, as theres currently no globaly
defined DPDK release version, its all just implicit, and driver versions aren't
really there either).  I'm also hesitant to include kernel dependencies without
defining exactly what they mean (just module dependencies, or feature
enablement, or something else?).  Once we define it though, adding it can be
easy.

Yup. I just think the shared/static difference needs to be sorted out
somehow, eg requiring user to know about DSOs is not human-friendly at all.
That's why I called for the higher level use-cases in my previous email.

I disagree with that.  While its reasonable to give users the convienience of
scanning the DT_NEEDED entries of a binary and scanning those DSO's.  If a user

Scanning DT_NEEDED is of course ok sane and right thing to do, its just not
sufficient.

But its the only sane thing we can do implicitly in the shared case, because we
know those drivers have to be resolved for the app to run.  In the
RTE_EAL_PMD_PATH or -d cases, we dont' know until runtime what drivers that will
include, and so reporting on hardware support prior to run time via scanning of
the application is erroneous.  The sane thing to do is scan the pmd DSO, which
is where the hardware support resides, and make it clear that, for an
application to get that hardware support, they need to either link dynamically
(via a DT_NEEDED entry), or specify it on the command line, or make sure its in
RTE_EAL_PMD_PATH (if the distribution set it, which so far, no one does).

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has to specify the PMD to load in an application (either on the command line or
via a configuration file), then its reasonable assume that they (a) know where

But when the PMD path is set (as it should be on a distro build), this is
all automatic with zero action or extra config required from the user.

Its not,  RHEL doesn't do it, Fedora Doesn't do it, Ubuntu doesn't do it.  Even

Again, check your facts please. I dont know about Ubuntu but Fedora and RHEL
do set it to make the damn thing actually work out of the box without
requiring the user to figure out magic -d arguments.

Yes, I stipulated to your quiet change above, though I take issue to your
referring to a command line argument as being 'magic' while being perfectly fine
with plugin loading happening automatically due to some internal library
configuration that is invisible to the end user.

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if it is, it doesn't imply an application will get that support, as the
directory contents may change between scanning and application run time.

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to find that pmd and (b) are savy enough to pass that same path to a hardware
info tool.  Thats the exact same way that modinfo works (save for the fact that
modinfo can implicitly check the running kernel version to find the appropriate
path for a modular driver).

The only other thing that seems reasonable to me would be to scan
LD_LIBRARY_PATH.  I would assume that, if an application is linked dynamically,
the individual DSO's (librte_sched.so, etc), need to be in LD_LIBRARY_PATH.  If
thats the case, then we can assume that the appropriate PMD DSO's are there too,
and we can search there.  We can also check the standard /usr/lib and /lib paths
with that.  I think that would make fairly good sense.

You really don't want go crashing through the potentially thousands of
libraries in the standard library path going "is it a pmd, no, is it a pmd,
no..."

What?  No.  You misunderstand.  In the above, all I'm saying is that if you
specify an application, you can scan LD_LIBRARY_PATH for libraries in the
DT_NEEDED list. I don't mean to say that we shoudl check _every_ library in
LD_LIBRARY_PATH, that would be crazy.  Of course, the same problem exists with
RTE_EAL_PMD_PATH.  In the current installation, all pmd libraries are co-located
with the rest of the dpdk library set, so RTE_EAL_PMD_PATH would have to be set
to whatever that installation path was.  And once thats done, we would have to
go crashing through every DPDK library to see if it was a pmd.  Thats just as
insane.

Yes I misunderstood what you meant by looking through LD_LIBRARY_PATH, and
you misunderstood what I meant by it. I guess we can agree on having
misunderstood each other :) RTE_EAL_PMD_PATH needs to point to a directory
where nothing but PMDs exist. That is the standard practise with plugins on
all userland software.

I suppose we did misunderstand each other.

Look, I think we're simply not going to agree on this issue at all.  What about
this in the way of compromise.  I simply am not comfortable with automatically
trying to guess what hardware support will exist in an application based on the
transient contents of a plugin directory, because of all the reasons we've
already gone over, but I do understand the desire to get information about what
_might_ be automatically loaded for an application.  what if we added a 'plugin
mode' to pmdinfo. In this mode you would dpecify a dpdk installation directory
and an appropriate mode option.  When specified pmdinfo would scan librte_eal in
the specified directory, looking for an exported json string that informs us of
the configured plugin directory.  If found, we iterate through all the libraries
there displaying hw support.  That allows you to query the plugin directory for
available hardware support, while not implying that the application is
guaranteed to get it (because you didn't specifically state on the command line
that you wanted to know about the applications hardware support).

Neil

	- Panu -

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Neil