* hurd/translator.mdwn: link to remap page. * hurd/translator/remap.mdwn: new page. Describe simple remap examples with how to use lwip with pfinet. Some example remap bugs. --- hurd/translator.mdwn | 1 + hurd/translator/remap.mdwn | 128 +++++++++++++++++++++++++++++++++++++ 2 files changed, 129 insertions(+) create mode 100644 hurd/translator/remap.mdwn
diff --git a/hurd/translator.mdwn b/hurd/translator.mdwn index fe00a644..ae368527 100644 --- a/hurd/translator.mdwn +++ b/hurd/translator.mdwn @@ -110,6 +110,7 @@ The [[concept|concepts]] of translators creates its own problems, too: * [[ftpfs]] * [[magic]] * [[mtab]] +* [[remap]] * [[unionfs]] * [[nfs]] * [[symlink]] diff --git a/hurd/translator/remap.mdwn b/hurd/translator/remap.mdwn new file mode 100644 index 00000000..7f38bb9f --- /dev/null +++ b/hurd/translator/remap.mdwn @@ -0,0 +1,128 @@ +[[!meta copyright="Copyright © 2024 Free Software Foundation, +Inc."]] + +[[!meta license="""[[!toggle id="license" text="GFDL 1.2+"]][[!toggleable +id="license" text="Permission is granted to copy, distribute and/or modify this +document under the terms of the GNU Free Documentation License, Version 1.2 or +any later version published by the Free Software Foundation; with no Invariant +Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the license +is included in the section entitled [[GNU Free Documentation +License|/fdl]]."]]"""]] + +[[!tag stable_URL]] + +The remap translator lets you remap directories. This translator is to +be used as a chroot, within which paths point to the same files as the +original root, except a given set of paths, which are remapped to given +paths. + +This translator completes the [[server +overriding|community/gsoc/project_ideas/server_overriding]] google +summer of code project. + +It is often desirable to execute a command in a transitory environment +with remapped files. The `remap` script lets you do this. + +# Example Uses + +## Run a command through a custom pflocal +<!-- https://lists.debian.org/debian-hurd/2016/08/msg00016.html --> + + $ cd /tmp + $ settrans -ac 1 ~/HURD-SRC/pflocal/pflocal + $ remap /servers/socket/1 /tmp/1 -- /bin/bash -c 'echo huhu world | wc' + 1 2 11 + +## remapping /bin/sh + +On Debian, `/bin/sh` points to `dash`. Maybe you would rather it +point to `bash`. + + $ ls -lha $(which sh) + lrwxr-xr-x 1 root root 4 Jun 5 04:08 /usr/bin/sh -> dash + $ remap /usr/bin/sh /bin/bash -- ls -lha /usr/bin/sh + +<!-- note that I could NOT get the above to work! --> + +## remapping python3 + +Perhaps you've want to use a python package that requires a python +feature that your distro does not yet support. Compiling this custom +python3 can be a little annoying, because `./configure` makes you +specify where all the various libraries are. It's much easier to just +remap. + +<!-- I've no idea is this works either --> + + $ remap /usr/bin/python3 $HOME/bin/python3-custom -- ./configure + $ remap /usr/bin/python3 $HOME/bin/python3-custom -- cool-package + +## Remapping `/servers/socket/2` and `26` for vpn/firewall + +TODO add an example here. + +## Use remap to debug lwip + +Suppose, you want to debug [[lwip|hurd/lwip]]. You could set `lwip` +on `/servers/socket/2`, but it's hard to use an OS, if your network is +buggy. It would be nice to use the stable `pfinet` and test `lwip` as +needed. You can use the `eth-multiplexer` combined with `remap` to +have such a configuration. First, use the `eth-multiplexer` to change +`pfinet`'s interface from `/dev/eth0` to `/dev/eth0m/0` + + # settrans -c /dev/eth0m /hurd/eth-multiplexer --interface=/dev/eth0 + +Now we configure own main Hurd system to use a virtual network +interface (e.g. `/dev/eth0m/0`) instead. On Debian/Hurd, this can be +accomplished using + + # ifdown /dev/eth0 + # sed -i -e s#/dev/eth0#/dev/eth0m/0# /etc/network/interfaces + # ifup /dev/eth0m/0 + +Then you can do set up `lwip` on `~/lwip/servers/socket{2,26}` +<!-- $ settrans -ac my2 path/to/my-ipstack -what -ever; --> + + $ settrans -c ~/lwip/servers/socket/2 /hurd/lwip -i \ + /dev/eth0m/1 -4 ~/lwip/servers/socket/2 \ + -6 ~/lwip/servers/socket/26 + $ settrans -c ~/lwip/servers/socket/26 /hurd/lwip -i \ + /dev/eth0m/1 -4 ~/lwip/servers/socket/2 \ + -6 ~/lwip/servers/socket/26 + $ remap /servers/socket/2 ~/lwip/servers/socket/2 -- \ + ping -c 3 gnu.org + +If you are running the Hurd in qemu, then you can skip setting up the +`eth-multiplexer` and just configure another virtual ethernet +interface: `eth1`. Then using `lwip` is as simple as: + + $ settrans -c ~/lwip/servers/socket/2 -i /dev/eth1 \ + -4 ~/lwip/servers/socket/2 -6 ~/lwip/servers/socket/26 + $ settrans -c ~/lwip/servers/socket/26 -i /dev/eth1 \ + -4 ~/lwip/servers/socket/2 -6 ~/lwip/servers/socket/26 + $ remap /servers/socket/2 $HOME/lwip/servers/socket/2 \ + -- ping -c 3 gnu.org + +Alternatively, you could also launch a subhurd whose's networking uses +lwip. The [[subhurd]] page should give you an idea of how to do this. + +## Make a sandbox + +TODO this doesn't work. Put in an actual example + + $ mkdir ~/sandbox + $ settrans $HOME/sandbox /hurd/remap "/hurd" "/dev/null" + +## remap example bugs + +Remap is written in a rather simplistic way. It should layer over the +filesystem in a better. These examples demonstrate some problems. + + $ remap /etc/motd /dev/null -- sh -c 'wc /etc/motd; cd /etc; wc motd;' + 0 0 0 /etc/motd + 7 40 284 motd + /bin/settrans: fsys_goaway: (ipc/mig) server died + + $ remap /usr/bin /dev/null -- uname -a + GNU pippin 0.9 GNU-Mach 1.8+git20240714-up-486/Hurd-0.9 i686-AT386 GNU + /bin/settrans: fsys_goaway: (ipc/mig) server died -- 2.45.2
