Function Pwritev2

pkg/sentry/syscalls/linux/sys_read_write.go:439–480

Pwritev2 implements Linux syscall pwritev2(2).

(t *kernel.Task, sysno uintptr, args arch.SyscallArguments)

// Pwritev2 implements Linux syscall pwritev2(2).
func Pwritev2(t *kernel.Task, sysno uintptr, args arch.SyscallArguments) (uintptr, *kernel.SyscallControl, error) {
	// While the glibc signature is
	// pwritev2(int fd, struct iovec* iov, int iov_cnt, off_t offset, int flags)
	// the actual syscall
	// (https://elixir.bootlin.com/linux/v5.5/source/fs/read_write.c#L1162)
	// splits the offset argument into a high/low value for compatibility with
	// 32-bit architectures. The flags argument is the 6th argument (index 5).
	fd := args[0].Int()
	addr := args[1].Pointer()
	iovcnt := int(args[2].Int())
	offset := args[3].Int64()
	flags := args[5].Int()

	file := t.GetFile(fd)
	if file == nil {
		return 0, nil, linuxerr.EBADF
	}
	defer file.DecRef(t)

	// Check that the offset is legitimate.
	if offset < -1 {
		return 0, nil, linuxerr.EINVAL
	}

	// Get the source of the write.
	src, err := t.IovecsIOSequence(addr, iovcnt, usermem.IOOpts{})
	if err != nil {
		return 0, nil, err
	}

	opts := vfs.WriteOptions{
		Flags: uint32(flags),
	}
	var n int64
	if offset == -1 {
		n, err = write(t, file, src, opts)
	} else {
		n, err = pwrite(t, file, src, offset, opts)
	}
	t.IOUsage().AccountWriteSyscall(n)
	return uintptr(n), nil, HandleIOError(t, n != 0, err, linuxerr.ERESTARTSYS, "pwritev2", file)
}

func pwrite(t *kernel.Task, file *vfs.FileDescription, src usermem.IOSequence, offset int64, opts vfs.WriteOptions) (int64, error) {
	n, err := file.PWrite(t, src, offset, opts)