Unwanted (VDI) present

Recently I was given a task to run a outdated piece of commercial software on a very outdated (in)famous operating system. Unlucky for me on the given VDI (VirtualBox disk image) the so-called “Guests Additions” that enabled “better” time synchronization were already installed.

Fighting VBox time

So, this is what I had to do to keep the old clock:

• turn off networking card in the virtual machine configuration, because we do not want the system to use NTP or other newt service to get the “new” time,
• disable getting the host’s clock time: VBoxManage setextradata "WinXP" "VBoxInternal/Devices/VMMDev/0/Config/GetHostTimeDisabled" 1,
• and… this magic: VBoxManage modifyvm "WinXP" --biossystemtimeoffset "-341597644449", this thing does the very weird thing of telling the virtual machine BIOS how much to set it back in time, the offset here is total milliseconds between some old date and current date.

Getting the old date

With the Python script snippet below you will get the milliseconds to set back the VirtualBox clock to 01.01.2012 01:00.

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from datetime import datetime

round((datetime.strptime("01.01.2012 01:00", "%d.%m.%Y %H:%M")
      - datetime.now()).total_seconds() * 1000)

Equality methods

By implementing a method for equality equal-to? and two extraction methods equal-hash-code-of and equal-secondary-hash-code-of we can define our own object comparison rules.

For more info see Object Equality and Hashing.

Consider the following example:

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(define integer%
  (class* object% (equal<%>)
    (super-new)

    (init-field [value 0])

    (define/public (equal-to? other-object recur)
      (= value (get-field value other-object)))

    (define/public (equal-hash-code-of hash-code)
      (hash-code value))

    (define/public (equal-secondary-hash-code-of hash-code)
      (hash-code value))))

If we create a new integer% object we can notice that it is not transparent (we can not inspect values of any of it’s fields).

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(new integer%)
;;  => (object:integer% ...)

But if we compare two fresh integer% objects they will be equal.

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(equal? (new integer%) (new integer%))
;;  => #true

Transparent class

A transparent cvlass is a class with the inspect expression valuye se to #false.

From Racket documentation Creating Classes:

Just as for structure types, an inspector controls access to the class’s fields, including private fields, and also affects comparisons using equal?.

Consider the following example:

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(define integer%
  (class object%

    (super-new)

    (inspect #false)

    (init-field [value 0])))

If we create a new integer% object we can see it’s field values.

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(new integer%)
;;  => (object:integer% 0)

And if we compare two fresh integer% objects they will be equal.

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(equal? (new integer%) (new integer%))
;;  => #true

I have moved my main Fediverse account from @xgqt@fosstodon.org to @xgqt@emacs.ch.

The new account’s RSS feed can be found at emacs.ch/users/xgqt.rss.

Config

First let’s prepare a suitable nginx configuration file.

This one is pretty bare but it works well for our case:

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worker_processes 1;
daemon off;
pid ./nginx/temp/nginx.pid;

error_log /dev/stdout info;

events {
    worker_connections 1024;
}

http {
    client_body_temp_path ./nginx/temp/client 1 2;
    proxy_temp_path ./nginx/temp/proxy;
    fastcgi_temp_path ./nginx/temp/fastcgi;
    uwsgi_temp_path ./nginx/temp/uwsgi;
    scgi_temp_path ./nginx/temp/scgi;

    server {
        listen 127.0.0.1:8080;
        server_name localhost;

        access_log /dev/stdout;
        error_log /dev/stdout info;

        root ./;

        location / {
            autoindex on;
        }
    }
}

Server config is set up for serving all static files from the current directory.

Startup

Preparation

Based on how you want to store _temp_path files it might be necessary to create (or clean up) additional directories, for example:

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rm -r ./nginx/temp
mkdir -p ./nginx/temp

Run in current directory

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nginx -c ./nginx.conf -p ./

BTW, you may want to replace ./ with "$(pwd)" and occurrences in the config with static paths.

Bonus: other simple servers

Some of no-dependency-except-itself http servers it’s good to know about:

Python http.server

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python3 -m http.server -b 127.0.0.1 8080

Busybox

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busybox httpd -f -p 127.0.0.1:8080 -v

You can read more about configuring busybox’s httpd on OpenWRT docs.

System preparation

Qemu

Emerge qemu with static-user USE enabled and your wanted architectures.

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app-emulation/qemu      QEMU_SOFTMMU_TARGETS: aarch64 arm x86_64
app-emulation/qemu      QEMU_USER_TARGETS: aarch64 arm x86_64

app-emulation/qemu      static-user
dev-libs/glib           static-libs
sys-apps/attr           static-libs
sys-libs/zlib           static-libs
dev-libs/libpcre2       static-libs

OpenRC

Enable qemu-binfmt:

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rc-update add qemu-binfmt default

Start qemu-binfmt:

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rc-service qemu-binfmt start

Chrooting

• select chroot location (eg /chroots/gentoo-arm64-musl-stable)
• unpack the desired rootfs
• create needed directories
  • mkdir -p /chroots/gentoo-arm64-musl-stable/var/cache/distfiles
• execute bwrap
  • with last ro-bind mount the qemu emulator binary (eg qemu-aarch64)
  • execute the mounted emulator binary giving it a shell program (eg bash)

Chroot with bwrap:

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bwrap                                                       \
    --bind /chroots/gentoo-arm64-musl-stable /              \
    --dev /dev                                              \
    --proc /proc                                            \
    --perms 1777 --tmpfs /dev/shm                           \
    --tmpfs /run                                            \
    --ro-bind /etc/resolv.conf /etc/resolv.conf             \
    --bind /var/cache/distfiles /var/cache/distfiles        \
    --ro-bind /usr/bin/qemu-aarch64 /usr/bin/qemu-aarch64   \
    /usr/bin/qemu-aarch64 /bin/bash -l