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package main
import (
"fmt"
"path/filepath"
"runtime"
"syscall"
"unsafe"
)
// truncateBasic opens a file, writes data, then truncates it via
// syscall.Truncate which uses SYS_TRUNCATE directly on amd64 (path-based).
func truncateBasic() error {
dir, cleanup, err := makeTempDir("truncate-basic")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "truncfile.txt")
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
if _, err := syscall.Write(fd, []byte("truncate this content")); err != nil {
syscall.Close(fd)
return fmt.Errorf("write: %w", err)
}
syscall.Close(fd)
return syscall.Truncate(path, 5)
}
// truncateFtruncate opens a file, writes data, then truncates it via
// syscall.Ftruncate which uses SYS_FTRUNCATE directly on amd64 (fd-based).
func truncateFtruncate() error {
dir, cleanup, err := makeTempDir("truncate-ftruncate")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "ftruncfile.txt")
fd, err := syscall.Open(path, syscall.O_RDWR|syscall.O_CREAT, 0o644)
if err != nil {
return fmt.Errorf("open: %w", err)
}
defer syscall.Close(fd)
if _, err := syscall.Write(fd, []byte("ftruncate this content")); err != nil {
return fmt.Errorf("write: %w", err)
}
return syscall.Ftruncate(fd, 5)
}
// truncateEnoent attempts to truncate a nonexistent file via raw SYS_TRUNCATE.
// The syscall fails with ENOENT, but ior captures the enter_truncate
// tracepoint because the path is read on entry.
func truncateEnoent() error {
dir, cleanup, err := makeTempDir("truncate-enoent")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "truncate-enoent-missing.txt")
pathBytes, err := syscall.BytePtrFromString(path)
if err != nil {
return fmt.Errorf("path bytes: %w", err)
}
// Retry a few times to make this test resilient under high integration
// parallelism where a single failed syscall event can be dropped.
for i := 0; i < 5; i++ {
_, _, errno := syscall.Syscall(syscall.SYS_TRUNCATE, uintptr(unsafe.Pointer(pathBytes)), 0, 0)
runtime.KeepAlive(pathBytes)
if errno == 0 {
return fmt.Errorf("expected ENOENT, but truncate succeeded")
}
}
return nil
}
// truncateFtruncateEbadf calls raw SYS_FTRUNCATE on an invalid fd (99999).
// The syscall fails with EBADF, but ior captures the enter_ftruncate
// tracepoint because it is recorded on syscall entry.
func truncateFtruncateEbadf() error {
_, _, errno := syscall.Syscall(syscall.SYS_FTRUNCATE, 99999, 0, 0)
if errno == 0 {
return fmt.Errorf("expected EBADF, but ftruncate succeeded")
}
return nil
}
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