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|
package main
import (
"fmt"
"path/filepath"
"syscall"
)
// fcntlDupfd uses fcntl F_DUPFD to duplicate a file descriptor.
func fcntlDupfd() error {
dir, cleanup, err := makeTempDir("fcntl-dupfd")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "fcntlfile.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)
newFd, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_DUPFD, 0)
if errno != 0 {
return fmt.Errorf("fcntl F_DUPFD: %w", errno)
}
defer syscall.Close(int(newFd))
if _, err := syscall.Write(int(newFd), []byte("via fcntl")); err != nil {
return fmt.Errorf("write via fcntl dup: %w", err)
}
return nil
}
// fcntlSetfl uses fcntl F_GETFL/F_SETFL to read and modify file status flags.
func fcntlSetfl() error {
dir, cleanup, err := makeTempDir("fcntl-setfl")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "fcntlsetflfile.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)
flags, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_GETFL, 0)
if errno != 0 {
return fmt.Errorf("fcntl F_GETFL: %w", errno)
}
_, _, errno = syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_SETFL, flags|syscall.O_APPEND)
if errno != 0 {
return fmt.Errorf("fcntl F_SETFL: %w", errno)
}
if _, err := syscall.Write(fd, []byte("appended via fcntl setfl")); err != nil {
return fmt.Errorf("write: %w", err)
}
return nil
}
// fcntlDupfdCloexec uses fcntl F_DUPFD_CLOEXEC to duplicate a file descriptor
// with the close-on-exec flag set.
func fcntlDupfdCloexec() error {
dir, cleanup, err := makeTempDir("fcntl-dupfd-cloexec")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "fcntlcloexecfile.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)
newFd, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_DUPFD_CLOEXEC, 0)
if errno != 0 {
return fmt.Errorf("fcntl F_DUPFD_CLOEXEC: %w", errno)
}
defer syscall.Close(int(newFd))
if _, err := syscall.Write(int(newFd), []byte("via fcntl dupfd cloexec")); err != nil {
return fmt.Errorf("write via fcntl dup cloexec: %w", err)
}
return nil
}
// fcntlInvalidFd calls fcntl F_GETFL on an invalid fd (99999).
// The syscall fails with EBADF, but ior should capture the enter_fcntl
// tracepoint because it is recorded on syscall entry.
func fcntlInvalidFd() error {
_, _, errno := syscall.Syscall(syscall.SYS_FCNTL, 99999, syscall.F_GETFL, 0)
if errno == 0 {
return fmt.Errorf("expected fcntl on invalid fd to fail")
}
return nil
}
// fcntlDupfdMax opens a file and calls fcntl F_DUPFD with a minfd value
// that exceeds the process RLIMIT_NOFILE. The kernel rejects this with
// EINVAL, but ior should capture the enter_fcntl tracepoint.
func fcntlDupfdMax() error {
dir, cleanup, err := makeTempDir("fcntl-dupfd-max")
if err != nil {
return err
}
defer cleanup()
path := filepath.Join(dir, "fcntldupfdmaxfile.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)
// Use a minfd far beyond any realistic RLIMIT_NOFILE.
_, _, errno := syscall.Syscall(syscall.SYS_FCNTL, uintptr(fd), syscall.F_DUPFD, 1<<30)
if errno == 0 {
return fmt.Errorf("expected fcntl F_DUPFD with extreme minfd to fail")
}
return nil
}
|
