On Mon, 2020-04-27 at 13:57 -0300, Dan Gora wrote: > On Mon, Apr 27, 2020 at 1:19 PM Luca Boccassi <bl...@debian.org> wrote: > > On Thu, 2020-04-23 at 14:38 -0300, Dan Gora wrote: > > > On Thu, Apr 23, 2020 at 12:59 PM Luca Boccassi <bl...@debian.org> wrote: > > > > > > /dev/urandom is basically only a different interface to the same > > > > > > underlying mechanism. > > > > > > > > This is not the whole story though - while the end result when all > > > > works is the same, there are important differences in getting there. > > > > There's a reason a programmatic interface was added - it's just better > > > > in general. > > > > Just to name one - opening files has implications for LSMs like > > > > SELinux. You now need a specific policy to allow it, which means > > > > applications that upgrade from one version of DPDK to the next will > > > > break. > > > > > > DPDK opens _tons_ of files. This would not be the first file that DPDK > > > has to open. And it's not like /dev/urandom is a new interface. It's > > > been around forever. > > > > That might be the case, but it is not reason in itself to make things > > harder. Especially in light of the new stability promise - this might > > or might not be considered part of it, but it's worth mentioning at the > > very least, as it has a real impact on users. > > "make things harder" seems especially subjective.. I would argue that > I am in fact making things much easier by removing unnecessary > dependecies
For someone with selinux, things would be harder. It's a consequence worth highlighting, that's all. > > > If this is such a major problem, then that would argue for using the > > > dlsym()/dlopen() method to try to find the getentropy glibc function > > > that I sent in v3 of these patches. > > > > > > > In general, I do not think we should go backwards. The programmatic > > > > interface to the random pools are good and we should use them by > > > > default - of course by all means add fallbacks to urandom if they are > > > > not available. > > > > > > The original problem was that the "programmatic interface to the > > > random pools" (that is, getentropy()) can only be determined at > > > compilation time and if found introduce a new dependency on glibc 2.25 > > > that can easily be avoided by emulating it (as I did here in v4 of the > > > patches) or by trying to dynamically find the symbol at run time using > > > dlopen()/dlsym() (as I did in v3 of the patches). > > > > > > > But as Stephen said glibc generally does not support compiling on new + > > > > running on old - so if it's not this that breaks, it will be something > > > > else. > > > > > > Well that's not necessarily true. Most glibc interfaces have been > > > around forever and you can easily see what versions of glibc are > > > needed by running ldd on your application. I don't see the point in > > > introducing a new dependency on a very recent version of glibc which > > > is not supported by all supported DPDK platforms when it can easily be > > > worked around. > > > > > > The issue here is that the original patch to add getentropy(): > > > 1) Added a _new_ dependency on glibc 2.25. > > > 2) Added a _new_ dependency that the rdseed CPU flag on the execution > > > machine has to match the complication machine. > > > 3) Has different behavior if the DPDK is compiled with meson or with > > > Make on the same complication platform. > > > > > > thanks, > > > dan > > > > Adding a new dependecy happens only when building with the new version > > of the library. If it's not available, then there's no new dependency. > > But you also do not get to use the new getentropy() if you happen to > compile on a system which does not have the latest glibc, or if you > use the makefile system.. And that's perfectly fine - backward compatibility workarounds are not a problem to me. > > It sounds to me like you are trying to add workarounds for issues in > > your downstream build/deployment model, where your build dependencies > > are newer than your runtime dependencies. This in general is rarely > > well supported. > > I am fully aware of that. I am not adding "workarounds", I am > eliminating unnecessary dependencies which probably never should have > been introduced in the first place. It's not unnecessary. It's a better interface, and worth using if available. > > Now I'm fine with adding workarounds as _fallbacks_ - what I am > > explicitly NACKing is forcibly restricting to the least common > > denominator because of issues in a third party build/deployment system > > that doesn't follow the common norm. > > ugh.. this is the exact _opposite_ of what this patch does. It is not > restricting anything to a least common denominator. It is allowing > the DPDK to use the "best" available function, regardless of the build > system. > > Restricting to the least common denominator is what the original patch did... This is restricting to the least common denominator of /dev/urandom, which is a bad interface, frail with issues that everybody is moving away from, in favour of the programmatic API that this patch is removing, in order to fix a corner case with a non-standard, third- party build system that downgrades dependencies at runtime vs build time. > > This is especially true when dealing with RNG APIs, where the tiniest > > and most innocent-looking mistake could have disastrous consequences. > > This does not change the functionality of the RNG at all. It just > makes it work in the way that it was intended. These changes were > only introduced into 19.08, so they are not historical artifacts or > anything. It's reimplementing a syscall using a different interface which has different semantics. A small mistake there is going to cost us dearly. -- Kind regards, Luca Boccassi
