On Sun, Feb 03, 2019 at 07:37:55AM +0200, Amir Goldstein wrote:
> Any access? or just execute? Can you share pr_debug output of access
> to file that is not execute?

Sure, same result (EPERM) there, here is the output and the changed Nix
expression (in case you want to reproduce it):

https://gist.github.com/aszlig/0b5ae4b03208a117b6f737772ff0eed8

I also added a stat on these files to check whether it happens there as well,
but it only occurs when reading them.

Here is the relevant pr_debug output:

open(000000007ee735e6[/regular_top/l], 0100000) -> (0000000080f3d7f9, 00)
open(00000000f7778f73[somesubdir/regular_sub/l], 0100000) -> (0000000080f3d7f9, 00)

> FWIW, I ran unionmount-testsuite (tweaked) with 9p as lower as it passed,
> so no obvious regressions with 9p as lower.

Okay, one other thing that I can think of is that might be triggering the issue
is that the Nix build process (on the host side) runs in a chroot with a few
separate namespaces[1], including a mount namespace.

a!

[1]: https://github.com/NixOS/nix/blob/92d08c02c84be34ec0df56ed718526c382845d1a/src/libstore/build.cc#L2216-L2218
-- 
aszlig
Universal dilettante