Misleading error message on keymgr import-bind

I tried importing a key pair created with BIND's dnssec-keygen and kept getting an error message saying Error (not exists); first I thought keymgr couldn't find the file, then I thought maybe it was the zone which didn't exist.

It turns out that it was a simple permission problem (EACCESS) so a Permission denied would have been clearer. To me. :-)

I found the problem using strace(1):

openat(AT_FDCWD, "/var/lib/knot/zones/bindkey/Kbb.tm.+008+40171.private", O_RDONLY) = -1 EACCES (Permission denied)
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 3), ...}) = 0
write(1, "Error (not exists)\n", 19Error (not exists)
)    = 19

After changing the ownership of the K*.{private,key} files the import succeeded

keymgr bb.tm import-bind Kbb.tm.+008+40171.private
6d572c90095de1abbb3c2e465e92719a3fa0cf14
OK

Maybe it would be possible to change the diagnostic. This is knot-2.9.5-1 installed from your copr.