Initial commit: Schunix as it stands before the SchOS rename

An x86-64 operating system built from xv6, now largely rewritten: SMP,
a copy-on-write root filesystem (SchFS), PCI/USB/virtio drivers, a TTF
rasteriser, and a Linux-numbered syscall ABI.

No history before this point -- the tree was never under version control.
This commit exists so the rename that follows has something to undo to.

tools/fbshot.ps1

@@ -0,0 +1,87 @@
+# Draw on /dev/fb0 and photograph the result.
+#
+# bootcheck -Fb proves fbinfo *ran* and that the numbers it read back are the
+# ones the bootloader programmed. It cannot prove the pixels landed where they
+# were meant to: a framebuffer written with the wrong stride still reports
+# every byte accepted, and the only symptom is a picture that shears
+# progressively down the screen. That is a thing you have to look at.
+#
+#   tools\fbshot.ps1              gradient through mmap
+#   tools\fbshot.ps1 -Mode bars   colour bars through write()
+
+param(
+    [ValidateSet('fill', 'bars')]
+    [string]$Mode = 'fill',
+    [int]$BootSeconds = 20,
+    [string]$Qemu = "$env:USERPROFILE\scoop\apps\qemu\current\qemu-system-x86_64.exe"
+)
+
+$ErrorActionPreference = 'Stop'
+$root = Split-Path $PSScriptRoot -Parent
+$hda  = Join-Path $root 'schunix.img'
+$hdb  = Join-Path $root 'build\fs.img'
+$log  = Join-Path $root 'build\fbshot.log'
+$ppm  = Join-Path $root "build\fb-$Mode.ppm"
+
+Remove-Item -Force $log, $ppm -ErrorAction SilentlyContinue
+
+$monPort = 55556      # not crashshot's 55555, so the two can run back to back
+
+$psi = New-Object System.Diagnostics.ProcessStartInfo
+$psi.FileName = $Qemu
+$psi.Arguments = @(
+    "-drive file=`"$hda`",format=raw,index=0,media=disk"
+    "-drive file=`"$hdb`",format=raw,index=1,media=disk"
+    '-m 1G -smp 1 -cpu qemu64,+rdtscp -machine pc-i440fx-9.2'
+    '-display none'
+    "-chardev stdio,id=c0,logfile=`"$log`""
+    '-serial chardev:c0'
+    "-monitor tcp:127.0.0.1:$monPort,server,nowait"
+) -join ' '
+$psi.RedirectStandardInput = $true
+$psi.UseShellExecute       = $false
+
+Write-Host "==> booting" -ForegroundColor Cyan
+$p = [System.Diagnostics.Process]::Start($psi)
+
+function Send-Line($text) {
+    foreach ($ch in ($text + "`n").ToCharArray()) {
+        $p.StandardInput.Write($ch)
+        $p.StandardInput.Flush()
+        Start-Sleep -Milliseconds 30    # serial has no flow control
+    }
+}
+
+try {
+    Start-Sleep -Seconds $BootSeconds
+    Write-Host "  > fbinfo $Mode" -ForegroundColor DarkGray
+    Send-Line "fbinfo $Mode"
+    Start-Sleep -Seconds 8              # 1.9 MB a pixel at a time is not fast
+
+    Write-Host "==> capturing the framebuffer" -ForegroundColor Cyan
+    $client = New-Object System.Net.Sockets.TcpClient('127.0.0.1', $monPort)
+    $writer = New-Object System.IO.StreamWriter($client.GetStream())
+    $writer.AutoFlush = $true
+    Start-Sleep -Milliseconds 500
+    $writer.WriteLine("screendump $ppm")
+    Start-Sleep -Seconds 2
+    $writer.WriteLine('quit')
+    Start-Sleep -Milliseconds 500
+    $client.Close()
+} finally {
+    if (-not $p.HasExited) { $p.Kill() }
+    Start-Sleep -Milliseconds 800
+}
+
+if (Test-Path $log) {
+    $text = Get-Content $log -Raw
+    $idx = $text.IndexOf('fbinfo')
+    if ($idx -ge 0) { Write-Host $text.Substring($idx) }
+}
+
+if (Test-Path $ppm) {
+    Write-Host "==> $ppm ($((Get-Item $ppm).Length) bytes)" -ForegroundColor Green
+} else {
+    Write-Host 'FAIL: no screendump was produced' -ForegroundColor Red
+    exit 1
+}