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diff --git a/dev/todo/install-bb-without-bb.mdwn b/dev/todo/install-bb-without-bb.mdwn new file mode 100644 index 0000000..4bb90ff --- /dev/null +++ b/dev/todo/install-bb-without-bb.mdwn @@ -0,0 +1,86 @@ +[[!meta title="Installing BusyBox Without BusyBox"]] + +**or, Adventures in Regressions and Crazy Ideas** + +--- + +**This work is now done.** + +**The rest of this page is kept only for reference and historical purposes.** + +--- + +Two Problems +============ + +`opkg-lede` and the Outsourced Inflation +---------------------------------------- + +`opkg-lede` [now relies][opkg-lede-dd4c78a] on an external `gzip` executable. +When upgrading a package, it tries to execute `gzip` to unpack maintainer +scripts and data files [after removing][opkg_install_pkg] the old version of the +package. When the package being upgraded is `busybox`, which provides `gzip`, +`opkg` crashes and leaves behind a completely broken system. + +To reiterate, `opkg-lede` is (and has been for as long as it has been in +ProteanOS) **currently unable to upgrade `busybox`**, due to its own design. + +[opkg-lede-dd4c78a]: https://git.openwrt.org/?p=project/opkg-lede.git;a=commitdiff;h=dd4c78aa88efd3b9cf516030937c684814df7962 +[opkg_install_pkg]: https://git.openwrt.org/?p=project/opkg-lede.git;a=blob;f=libopkg/opkg_install.c;hb=d4ba162#l1520 + +The Amazing Alternatives of `busybox` +------------------------------------- + +Instead of [adding alternatives][alts-log] one at a time, [it would be +nice][bb-ua] to manage all of `busybox`'s utility links using +`update-alternatives`. Unfortunately, the [maintainer script][bb.pi] that runs +`update-alternatives` (as well as the [`update-alternatives` script][u-a] +itself) needs a few `busybox` utilities (`/bin/sh` for a start). Thus, after an +older version of `busybox` is deconfigured, a newer version can't be configured. +`busybox` also can't be configured when first unpacked by `prokit`. + +[alts-log]: http://git.proteanos.com/pkg/busybox.git/log/alternatives +[bb-ua]: http://git.proteanos.com/pkg/busybox.git/commit/?id=1558d05c62ed90f7d93a14533541c33896b7b733 +[bb.pi]: http://git.proteanos.com/pkg/busybox.git/tree/busybox.pkg/postinst +[u-a]: https://git.openwrt.org/?p=project/opkg-lede.git;a=blob;f=utils/update-alternatives.in;hb=d4ba162 + +One Solution +============ + +The next version of `src:opkg-lede` (likely 0+git20190131.d4ba162-7) already +will have a [wrapper script called `opkg`][opkg] that executes `opkg-cl` (the +actual binary executable). The script can be extended to first save a copy of +`/bin/busybox` to an empty temporary directory, generate utility links to it in +the directory, and add the directory to `PATH`. Until all of this setup is +complete, the wrapper script must be careful to execute utilities as `busybox +$util` (a full path to `busybox` won't be necessary, as the usual `/bin/busybox` +will be available at that point). This includes the interpreter line, which +will need to be changed to `#!/bin/busybox sh`. `ash` built-in utilities can be +used as usual. + +The `busybox` package can't use `update-alternatives` to manage all of its +utility links until an `opkg-lede` with this wrapper script functionality is +uploaded. This is because, even if `busybox`'s `postinst` script is modified to +use the `busybox` executable directly, other packages' maintainer scripts may be +executed first, while `busybox` is unpacked but not yet configured (and +therefore utility links are not yet created). + +Once this new `opkg-lede` package is uploaded and `busybox` uses +`update-alternatives` for everything, `busybox` would need to declare that it +`Breaks` older versions of `opkg-lede`, to ensure that `opkg-lede` will preserve +a copy of the `busybox` executable and its utility links. However, this is +still insufficient, as the version of `opkg` that is *running* must have already +set up this environment before `busybox` is upgraded. `busybox`'s `prerm` +script will need to check for this somehow and abort the upgrade if `opkg` is +too old to have prepared for a safe upgrade. One solution is for the `opkg` +script to set an `OPKG_BUSYBOX_SAVED` environment variable. + +The `opkg` script of the `opkg-lede` package will need to read `busybox`'s list +of alternatives links. This is currently located at +`/usr/share/busybox/alternatives`. [The file's format][alts] will change when +`busybox` uses `update-alternatives` for everything: the last two columns (name +and priority) will be dropped. `opkg` however can simply read the first column, +so it will maintain compatibility. + +[opkg]: http://git.proteanos.com/pkg/opkg-lede.git/tree/opkg +[alts]: http://git.proteanos.com/pkg/busybox.git/tree/alternatives?id=e37f03311d934a8f33a9ff31db47b18bbf0be555 |