Re: [cmake] Problem with dependencies for configure checks

From: Andrey Semashev (andrey.semashev_at_[hidden])
Date: 2021-06-04 12:04:56

On 6/4/21 2:03 PM, Niall Douglas via Boost wrote:
> On 04/06/2021 10:12, Andrey Semashev via Boost wrote:
> 
>> My stance on this is that Boost.Filesystem must be built on a system
>> with kernel headers matching or older than the systems that will run the
>> binary. This matches the same requirements for Windows. I don't support
>> configs with headers newer than runtime kernel.
> 
> It's trivially easy to do a runtime check for statx kernel support and
> fall back on older syscalls if needed.
> 
> This is LLFIO doing so, and it works on Linux kernel 2.6:
> 
> https://github.com/ned14/llfio/blob/develop/include/llfio/v2.0/detail/impl/posix/stat.ipp#L205

The code you pointed to is not what I would call trivial. There are 
quite a few places where statx is used in Boost.Filesystem, in some 
places exclusively (i.e. there is no fallback). I could add a runtime 
check, but I definitely don't want that check to happen on every call. 
This means the result must be stored globally in a thread-safe manner. 
Then there are other syscalls, on Linux and other systems, should I also 
add runtime checks for those? All that to support what I consider 
improperly configured systems. It just doesn't look like a worthwhile 
effort while I have other things to do, including in Boost.Filesystem too.