tvl-depot/tvix/boot/tvix-init.go

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package main
import (
"fmt"
"log"
"os"
"os/exec"
"strings"
"syscall"
)
// run the given command, connecting std{in,err,out} with the OS one.
func run(args ...string) error {
cmd := exec.Command(args[0], args[1:]...)
cmd.Stdin = os.Stdin
cmd.Stderr = os.Stderr
cmd.Stdout = os.Stdout
return cmd.Run()
}
// parse the cmdline, return a map[string]string.
func parseCmdline(cmdline string) map[string]string {
line := strings.TrimSuffix(cmdline, "\n")
fields := strings.Fields(line)
out := make(map[string]string, 0)
for _, arg := range fields {
kv := strings.SplitN(arg, "=", 2)
switch len(kv) {
case 1:
out[kv[0]] = ""
case 2:
out[kv[0]] = kv[1]
}
}
return out
}
// mounts the nix store from the virtiofs tag to the given destination,
// creating the destination if it doesn't exist already.
func mountTvixStore(dest string) error {
if err := os.MkdirAll(dest, os.ModePerm); err != nil {
return fmt.Errorf("unable to mkdir dest: %w", err)
}
if err := run("mount", "-t", "virtiofs", "tvix", dest, "-o", "ro"); err != nil {
return fmt.Errorf("unable to run mount: %w", err)
}
return nil
}
func main() {
fmt.Print(`
______ _ ____ _ __
/_ __/ __(_) __ / _/___ (_) /_
/ / | | / / / |/_/ / // __ \/ / __/
/ / | |/ / /> < _/ // / / / / /_
/_/ |___/_/_/|_| /___/_/ /_/_/\__/
`)
// Set PATH to "/bbin", so we can find the u-root tools
os.Setenv("PATH", "/bbin")
if err := run("mount", "-t", "proc", "none", "/proc"); err != nil {
log.Printf("Failed to mount /proc: %v\n", err)
}
if err := run("mount", "-t", "sysfs", "none", "/sys"); err != nil {
log.Printf("Failed to mount /sys: %v\n", err)
}
if err := run("mount", "-t", "devtmpfs", "devtmpfs", "/dev"); err != nil {
log.Printf("Failed to mount /dev: %v\n", err)
}
cmdline, err := os.ReadFile("/proc/cmdline")
if err != nil {
log.Printf("Failed to read cmdline: %s\n", err)
}
cmdlineFields := parseCmdline(string(cmdline))
if _, ok := cmdlineFields["tvix.find"]; ok {
// If tvix.find is set, invoke find /nix/store
if err := mountTvixStore("/nix/store"); err != nil {
log.Printf("Failed to mount tvix store: %v\n", err)
}
if err := run("find", "/nix/store"); err != nil {
log.Printf("Failed to run find command: %s\n", err)
}
} else if _, ok := cmdlineFields["tvix.shell"]; ok {
// If tvix.shell is set, mount the nix store to /nix/store directly,
// then invoke the elvish shell
if err := mountTvixStore("/nix/store"); err != nil {
log.Printf("Failed to mount tvix store: %v\n", err)
}
if err := run("elvish"); err != nil {
log.Printf("Failed to run shell: %s\n", err)
}
} else if v, ok := cmdlineFields["tvix.run"]; ok {
// If tvix.run is set, mount the nix store to /nix/store directly,
// then invoke the command.
if err := mountTvixStore("/nix/store"); err != nil {
log.Printf("Failed to mount tvix store: %v\n", err)
}
if err := run(v); err != nil {
log.Printf("Failed to run command: %s\n", err)
}
} else if v, ok := cmdlineFields["init"]; ok {
// If init is set, invoke the binary specified (with switch_root),
// and prepare /fs beforehand as well.
os.Mkdir("/fs", os.ModePerm)
if err := run("mount", "-t", "tmpfs", "none", "/fs"); err != nil {
log.Fatalf("Failed to mount /fs tmpfs: %s\n", err)
}
// Mount /fs/nix/store
if err := mountTvixStore("/fs/nix/store"); err != nil {
log.Fatalf("Failed to mount tvix store: %v\n", err)
}
// Invoke switch_root, which will take care of moving /proc, /sys and /dev.
if err := syscall.Exec("/bbin/switch_root", []string{"switch_root", "/fs", v}, []string{}); err != nil {
log.Printf("Failed to switch root: %s\n", err)
}
} else {
log.Printf("No command detected, not knowing what to do!")
}
// This is only reached in the non switch_root case.
log.Printf("Nothing left to be done, powering off.")
if err := run("poweroff"); err != nil {
log.Printf("Failed to run poweroff command: %v\n", err)
}
}