On Mon, Jan 11, 2021 at 03:06:28PM +0100, Bartosz Golaszewski wrote:

On Mon, Jan 11, 2021 at 2:45 PM Andy Shevchenko
[off-list ref] wrote:

quoted

On Mon, Jan 11, 2021 at 3:37 PM Bartosz Golaszewski [off-list ref] wrote:

quoted

From: Bartosz Golaszewski <redacted>

In order to avoid any problems with symbols missing from the host linux
kernel headers (for example: if current version of libgpiod supports
features that were added recently to the kernel but the host headers are
outdated and don't export required symbols) let's add the uapi header to
the repository and include it instead of the one in /usr/include/linux.

I doubt this is a good decision. First of all if the host (or rather
target, because host should not influence build of libgpiod) has

I meant the host as in: the machine on which you build and which
contains the headers for the target as well but I see what you mean.

quoted

outdated header it may be for a reason (it runs old kernel).
When you run new library on outdated kernel it might produce various
of interesting errors (in general, I haven't investigated libgpiod
case).
On top of that you make a copy'n'paste source code which is against
the Unix way.

Sorry, but I'm in favour of dropping this one.

Cc: Thomas

This problem has been raised by the buildroot people when we started
requiring different versions of kernel headers to build v1.4 and v1.6.
It turns out most projects simply package the uapi headers together
with their sources (e.g. wpa_supplicant, libnl, iproute2) to avoid
complicated dependencies. It's true that now the library can fail at
runtime but I'm fine with that. Also: if we add new features between
two kernel versions, we still allow to build the new library version
except that these new features won't work on older kernels.

I see.

So known ways to solve this are
 - provide a header with source tree (see above)
 - modify code with ifdeffery against specific kernel versions
 - ...something else... ?

Second item is what ALSA used (not sure if they provide a standalone driver
anymore). Ugly, but won't require header which may be staled.

Any other solutions in mind?


-- 
With Best Regards,
Andy Shevchenko