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From: Dan Gora <dg@adax.com>
To: Mattias Rönnblom <mattias.ronnblom@ericsson.com>
Cc: "dev@dpdk.org" <dev@dpdk.org>,
	David Marchand <david.marchand@redhat.com>,
	 Jerin Jacob <jerinjacobk@gmail.com>
Subject: Re: [dpdk-dev] [PATCH 2/2] eal: resolve getentropy at run time for random seed
Date: Wed, 22 Apr 2020 17:35:05 -0300
Message-ID: <CAGyogRb=uGbBsVgMycgLy93EzLafP78xjOX910Yct_1AoxZORg@mail.gmail.com> (raw)
In-Reply-To: <80e5cf97-feae-c753-5c65-4f3b121729f3@ericsson.com>

On Wed, Apr 22, 2020 at 5:14 PM Mattias Rönnblom
<mattias.ronnblom@ericsson.com> wrote:
>
> On 2020-04-22 19:44, Dan Gora wrote:
> > On Wed, Apr 22, 2020 at 5:28 AM Mattias Rönnblom
> > <mattias.ronnblom@ericsson.com> wrote:
> >> On 2020-04-21 21:54, Dan Gora wrote:
> >>> The getentropy() function was introduced into glibc v2.25 and so is
> >>> not available on all supported platforms.  Previously, if DPDK was
> >>> compiled (using meson) on a system which has getentropy(), it would
> >>> introduce a dependency on glibc v2.25 which would prevent that binary
> >>> from running on a system with an older glibc.  Similarly if DPDK was
> >>> compiled on a system which did not have getentropy(), getentropy()
> >>> could not be used even if the execution system supported it.
> >>>
> >>> Introduce a new static function, __rte_getentropy() which will try to
> >>> resolve the getentropy() function dynamically using dlopen()/dlsym(),
> >>> returning failure if the getentropy() function cannot be resolved or
> >>> if it fails.
> >>
> >> Two other options: providing a DPDK-native syscall wrapper for
> >> getrandom(), or falling back to reading /dev/urandom. Have you
> >> considered any of those two options? If so, why do you prefer
> >> dlopen()/dlsym()?
> > I didn't give any thought at all to using /dev/urandom.  The goal was
> > not really to change how the thing worked, just to remove the
> > dependency on glibc 2.25.
>
>
> /dev/urandom is basically only a different interface to the same
> underlying mechanism.
>
> Such an alternative would look something like:
>
> static int
> getentropy(void *buffer, size_t length)
> {
>          int rc = -1;
>          int old_errno = errno;
>          int fd;
>
>          fd = open("/dev/urandom", O_RDONLY);
>
>          if (fd < 0)
>                  goto out;
>
>          if (read(fd, buffer, length) != length)
>                  goto out_close;
>
>          rc = 0;
>
> out_close:
>          close(fd);
> out:
>          errno = old_errno;
>
>          return rc;
> }

That's fine with me, but like I said I wasn't trying to change how any
of this worked, just work around glibc dependencies.  There seems to
be some subtle difference between /dev/urandom and /dev/random, but...

https://patches-gcc.linaro.org/comment/14484/

> >> Failure to run on old libc seems like a non-issue to me.
> > Well, again, it's a new dependency that didn't exist before.. We sell
> > to telco customers, so we have to support 10s of different target
> > platforms of various ages.  If they update their system, we'd have to
> > recompile our code to be able to use getentropy().  Similarly, if we
> > compiled on a system which has getentropy(), but the target system
> > doesn't, then they cannot run our binary because of the glibc 2.25
> > dependency.  That means that we have to have separate versions with
> > and without getentropy().  It's a maintenance headache for no real
> > benefit.
>
>
> I'm not sure I follow. Why would you need to recompile DPDK in case they
> upgrade their system? It sounds like you care about initial seeding,
> since you want getentropy() if it exists, but then in the next paragraph
> you want to throw it out, so I'm a little confused.

Well  _I_ wouldn't but maybe someone wants getentropy() for the
initial seed.. I assume that's why it was added in the first place..
For my application we don't care at all.  I just want to get rid of
this dependency on glibc 2.25 and have the behavior be the same on
meson and Makefile builds on the same complication system.

> Why doesn't the standard practice of compiling against the oldest
> supported libc work for you?

I guess I didn't realize that was "standard practice" but even so it
still adds an unnecessary restriction on the complication platform.

> > To my mind, since getentropy() can block it seems like it would
> > probably be better to just remove it entirely, but I suppose that's up
> > to the person(s) who put it in in the first place.
>
>
> Maybe I'm wrong, but I found it unlikely that a DPDK application would
> start before the entropy pool was initialized. After this point,
> getentropy() will not block. Do you consider this a real problem?

Not really.. I don't know the original motivations for adding
getentropy() in the first place.  I assumed that there was some good
reason.  If there's not we could just back out all of these
complications and revert commit faf8fd252785ee8b1 (et al...)

Again, I don't have any dog in the fight about how to get the seed, I
just wanted to remove the glibc dependency and the different behavior
for Makefile and meson builds on the same complication system.

For me, using dlsym() or reading from /dev/[u]random is 6 for half a
dozen.  Both have precedents in other places in the DPDK code base.  I
can fix it either way.

thanks
dan

  reply	other threads:[~2020-04-22 20:35 UTC|newest]

Thread overview: 47+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-04-21 19:54 [dpdk-dev] [PATCH 0/2] eal: choose initial PRNG seed source at runtime Dan Gora
2020-04-21 19:54 ` [dpdk-dev] [PATCH 1/2] eal: check for rdseed at run time for random seed Dan Gora
2020-04-22  8:22   ` Mattias Rönnblom
2020-04-21 19:54 ` [dpdk-dev] [PATCH 2/2] eal: resolve getentropy " Dan Gora
2020-04-21 21:03   ` Stephen Hemminger
2020-04-21 21:08     ` Dan Gora
2020-04-22  8:28   ` Mattias Rönnblom
2020-04-22 17:44     ` Dan Gora
2020-04-22 20:14       ` Mattias Rönnblom
2020-04-22 20:35         ` Dan Gora [this message]
2020-04-23 10:04           ` Luca Boccassi
2020-04-23 17:38             ` Dan Gora
2020-04-27 12:44               ` Luca Boccassi
2020-04-27 16:57                 ` Dan Gora
2020-04-30  8:41                   ` Luca Boccassi
2020-04-30 20:43                     ` Dan Gora
2020-05-01 10:33                       ` Luca Boccassi
2020-05-01 21:05                         ` Dan Gora
2020-05-04  8:04                           ` Mattias Rönnblom
2020-05-04 14:13                             ` Dan Gora
2020-05-04 14:19                               ` Dan Gora
2020-06-02  5:10                                 ` Dan Gora
2020-06-09 15:37                                   ` Dan Gora
2020-06-10  8:15                                     ` Thomas Monjalon
2020-06-10  8:33                                       ` Luca Boccassi
2020-06-10  8:07                               ` Thomas Monjalon
2020-04-23 12:36           ` Mattias Rönnblom
2020-04-23 17:27             ` Dan Gora
2020-04-21 20:41 ` [dpdk-dev] [PATCH v2 0/2] eal: choose initial PRNG seed source at runtime Dan Gora
2020-04-21 20:41   ` [dpdk-dev] [PATCH v2 1/2] eal: check for rdseed at run time for random seed Dan Gora
2020-04-21 20:41   ` [dpdk-dev] [PATCH v2 2/2] eal: resolve getentropy " Dan Gora
2020-04-22 18:15 ` [dpdk-dev] [PATCH v3 0/2] eal: choose initial PRNG seed source at runtime Dan Gora
2020-04-22 18:15   ` [dpdk-dev] [PATCH v3 1/2] eal: check for rdseed at run time for random seed Dan Gora
2020-04-22 18:15   ` [dpdk-dev] [PATCH v3 2/2] eal: resolve getentropy " Dan Gora
2020-04-22 23:42 ` [dpdk-dev] [PATCH v4 0/2] eal: choose initial PRNG seed source at runtime Dan Gora
2020-04-22 23:42   ` [dpdk-dev] [PATCH v4 1/2] eal: check for rdseed at run time for random seed Dan Gora
2020-04-22 23:42   ` [dpdk-dev] [PATCH v4 2/2] eal: emulate glibc getentropy for initial " Dan Gora
2020-04-23  2:39     ` Stephen Hemminger
2020-04-23 17:42       ` Dan Gora
2020-06-29  9:30     ` Mattias Rönnblom
2020-06-29 17:57       ` Dan Gora
2020-06-29 20:57         ` Mattias Rönnblom
2020-06-29  9:32   ` [dpdk-dev] [PATCH v4 0/2] eal: choose initial PRNG seed source at runtime Mattias Rönnblom
2020-06-29 18:01     ` Dan Gora
2020-06-29 18:04       ` Dan Gora
2020-06-29 21:05       ` Mattias Rönnblom
2020-06-29 21:14         ` Dan Gora

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