netns=myns
find -L /proc/[1-9]*/task/*/ns/net -samefile /run/netns/"$netns" | cut -d/ -f5

print -l /proc/[1-9]*/task/*/ns/net(e:'[ $REPLY -ef /run/netns/$netns ]'::h:h:t)

sudo ip netns exec "$netns" socat abstract-listen:test-ns,fork /dev/null &
ps -eopid= |
  while read p; do
    nsenter -n"/proc/$p/ns/net" socat -u abstract:test-ns - 2> /dev/null &&
      echo "$p"
  done

netns=mynamespace
inode=$(ls -i /var/run/netns/$netns | cut -f1 -d" ")
pids=$(find -L /proc/[1-9]*/task/*/ns/net -inum $inode | cut -f3 -d"/" | uniq)
ps -p $pids

PID  Namespace             Thread/Command
        --  net:[4026533172]      created by ip netns add qrouter-c33ffc14-dbc2-4730-b787-4747
        --  net:[4026533112]      created by ip netns add qrouter-5a691ed3-f6d3-4346-891a-3b59
       297  mnt:[4026531856]      kdevtmpfs
      3429  net:[4026533050]**    dnsmasq --no-hosts --no-resolv --strict-order --bind-interfa
      3429  mnt:[4026533108]      dnsmasq --no-hosts --no-resolv --strict-order --bind-interfa
      3486  net:[4026533050]**    /usr/bin/python /usr/bin/neutron-ns-metadata-proxy --pid_fil
      3486  mnt:[4026533107]      /usr/bin/python /usr/bin/neutron-ns-metadata-proxy --pid_fil