repro.go

package main

import (
	"fmt"
	"math/rand"
	"os"
	"path/filepath"
	"strconv"
)

var (
	// dumpMagic is a dataset dump header to sanity check a data dump.
	dumpMagic = []uint32{0xbaddcafe, 0xfee1dead}
)

func main() {
	if err := runit(); err != nil {
		fmt.Fprintf(os.Stderr, "Error: %v\n", err)
		os.Exit(1)
	}
}

func runit() error {
	dir := os.TempDir()
	size := 10 * 1_073_739_912 // A bit north of 10Gb
	path := filepath.Join(dir, fmt.Sprintf("cachefile"))
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return err
	}
	// Create a huge temporary empty file to fill with data
	temp := path + "." + strconv.Itoa(rand.Int())
	dump, err := os.Create(temp)
	if err != nil {
		return err
	}
	fSize := uint64(len(dumpMagic))*4 + uint64(size)
	if p := uint64(os.Getpagesize()); p > 0 {
		fSize = p * ((fSize + p - 1) / p)
	}
	// write to the end of the file
	if _, err := dump.WriteAt(make([]byte, 1000), int64(fSize-1000)); err != nil {
		return fmt.Errorf("Writing to EOF failed: %v", err)
	}
	fmt.Printf("Writing to EOF worked fine\n")
	// fill with zeroes
	for i := uint64(0); i < fSize-1000; i += 1000 {
		if _, err := dump.Write(make([]byte, 1000)); err != nil {
			return fmt.Errorf("Error at i=%d: %w", i, err)
		}
	}
	err = dump.Sync()
	fmt.Printf("Did sync, err = %v\n", err)
	fmt.Printf("Did truncate file %s size %d pageSize %d\n", path, int64(fSize), os.Getpagesize())
	return nil
}

Writing to EOF worked fine
Error: Error at i=1071734000: write /tmp/cachefile.5577006791947779410: no space left on device