Libguestfs - Feb 2023 - [libnbd PATCH v3 09/29] lib/utils: introduce async-signal-safe execvpe()

On 2/21/23 19:04, Daniel P. Berrang? wrote:
> AFAIK, libnbd/nbdkit haven't made a statement about what platforms
> they aim to target. In my response I'm more or less assuming though
> that you would only care about similar modern platforms to QEMU/libvirt,
> and thus POSIX conformance would not be needed in all areas. Maybe
> libnbd/nbdkit want to be more explicit about what they target as
> platforms to make the portability requirements clear to contributors ?
libnbd's README.md requires

* Linux, FreeBSD or OpenBSD.
  Other OSes may also work but we have only tested these three.
* GCC or Clang
* GNU make
* bash
* [...]

nbdkit's requires

* Linux, macOS, Windows, FreeBSD, OpenBSD or Haiku
* GCC or Clang
* bash
* GNU make
* [...]

To me, anything beyond Linux on those OS lists is entirely untestable
*locally*, hence my reliance on POSIX. CI is a horrible way (compared to
a published technical standard) to figure out whether each individual
interface works as needed everywhere, even just across this small set of
OSes. Having to look at multiple OS manual pages is just slightly less
horrible (and I consider those less trustworthy than POSIX; see again
the conflict between the linux man pages and the glibc documentation
from GNU). The POSIX people have done *huge work* to save us that effort.

Sticking with POSIX might make us work more (as in, write technically
superfluous code), but I've always felt fewer nasty surprises are
waiting to ambush us that way.

I don't think we have documentation that describes the broadest
intersection of these OSes specifically. (We don't even have
conflict-free documentation just for Linux!)

Laszlo

On Tue, Feb 21, 2023 at 11:59:30PM +0100, Laszlo Ersek
wrote:
> On 2/21/23 19:04, Daniel P. Berrang? wrote:
> 
> > AFAIK, libnbd/nbdkit haven't made a statement about what platforms
> > they aim to target. In my response I'm more or less assuming
though
> > that you would only care about similar modern platforms to
QEMU/libvirt,
> > and thus POSIX conformance would not be needed in all areas. Maybe
> > libnbd/nbdkit want to be more explicit about what they target as
> > platforms to make the portability requirements clear to contributors ?
> 
> libnbd's README.md requires
> 
> * Linux, FreeBSD or OpenBSD.
>   Other OSes may also work but we have only tested these three.
> * GCC or Clang
> * GNU make
> * bash
> * [...]
> 
> nbdkit's requires
> 
> * Linux, macOS, Windows, FreeBSD, OpenBSD or Haiku
> * GCC or Clang
> * bash
> * GNU make
> * [...]
> 
> To me, anything beyond Linux on those OS lists is entirely untestable
> *locally*, hence my reliance on POSIX. CI is a horrible way (compared to
> a published technical standard) to figure out whether each individual
> interface works as needed everywhere, even just across this small set of
> OSes. Having to look at multiple OS manual pages is just slightly less
> horrible (and I consider those less trustworthy than POSIX; see again
> the conflict between the linux man pages and the glibc documentation
> from GNU). The POSIX people have done *huge work* to save us that effort.
FWIW, my (bitter) experience from both libvirt and QEMU is that unless
you have CI validating it, you don't have portability to a platform, no
matter how much effort the developers put in complying with standards
and/or manual pages. The reality of bizarre/broken platform impls always
gets in the way of good intentions.

FWIW, in terms of testing locally, all those platforms are trivial,
with the exception of macOS. For Windows, mingw toolchain will get
you through all compilation portability problems which is 90% of the
work. While you can use WINE for some functional testing, a real
Windows VM is better.  For the *BSD / Haiku, a VM can be spun up
with KVM quite easily.

macOS is the real pain point because of its restrictive EULA
meaning you basically have to buy it. It makes it very much a second
class citizen for developers, unless they happen to have personal
apple hardware.

With regards,
Daniel
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