Re: [PATCH] kcov: refactor common handle ID into kcov_common_handle_id

[Dmitry Vyukov]

On Thu, 30 Apr 2026 at 16:15, Jann Horn <jannh@xxxxxxxxxx> wrote:
>
> Store common handle IDs in "struct kcov_common_handle_id", which consumes
> no space in non-KCOV builds.
> This cleanup removes #ifdef boilerplate code from subsystems that
> integrate with KCOV (in particular in usbip_common.h and skbuff.h, see the
> diffstat).
> This should also make it easier to add KCOV remote coverage to more
> subsystems in the future.
>
> Signed-off-by: Jann Horn <jannh@xxxxxxxxxx>

Reviewed-by: Dmitry Vyukov <dvyukov@xxxxxxxxxx>

Thanks!

> ---
>  drivers/usb/usbip/usbip_common.h | 29 +----------------------------
>  drivers/usb/usbip/vhci_rx.c      |  4 ++--
>  drivers/usb/usbip/vhci_sysfs.c   |  2 +-
>  drivers/vhost/vhost.h            |  2 +-
>  include/linux/kcov.h             | 12 ++++++------
>  include/linux/skbuff.h           | 14 +++-----------
>  include/linux/types.h            |  6 ++++++
>  kernel/kcov.c                    |  6 +++---
>  8 files changed, 23 insertions(+), 52 deletions(-)
>
> diff --git a/drivers/usb/usbip/usbip_common.h b/drivers/usb/usbip/usbip_common.h
> index 282efca64a01..be4c5e65a7f8 100644
> --- a/drivers/usb/usbip/usbip_common.h
> +++ b/drivers/usb/usbip/usbip_common.h
> @@ -282,9 +282,7 @@ struct usbip_device {
>                 void (*unusable)(struct usbip_device *);
>         } eh_ops;
>
> -#ifdef CONFIG_KCOV
> -       u64 kcov_handle;
> -#endif
> +       struct kcov_common_handle_id kcov_handle;
>  };
>
>  #define kthread_get_run(threadfn, data, namefmt, ...)                     \
> @@ -339,29 +337,4 @@ static inline int interface_to_devnum(struct usb_interface *interface)
>         return udev->devnum;
>  }
>
> -#ifdef CONFIG_KCOV
> -
> -static inline void usbip_kcov_handle_init(struct usbip_device *ud)
> -{
> -       ud->kcov_handle = kcov_common_handle();
> -}
> -
> -static inline void usbip_kcov_remote_start(struct usbip_device *ud)
> -{
> -       kcov_remote_start_common(ud->kcov_handle);
> -}
> -
> -static inline void usbip_kcov_remote_stop(void)
> -{
> -       kcov_remote_stop();
> -}
> -
> -#else /* CONFIG_KCOV */
> -
> -static inline void usbip_kcov_handle_init(struct usbip_device *ud) { }
> -static inline void usbip_kcov_remote_start(struct usbip_device *ud) { }
> -static inline void usbip_kcov_remote_stop(void) { }
> -
> -#endif /* CONFIG_KCOV */
> -
>  #endif /* __USBIP_COMMON_H */
> diff --git a/drivers/usb/usbip/vhci_rx.c b/drivers/usb/usbip/vhci_rx.c
> index a75f4a898a41..a678e7c89837 100644
> --- a/drivers/usb/usbip/vhci_rx.c
> +++ b/drivers/usb/usbip/vhci_rx.c
> @@ -261,9 +261,9 @@ int vhci_rx_loop(void *data)
>                 if (usbip_event_happened(ud))
>                         break;
>
> -               usbip_kcov_remote_start(ud);
> +               kcov_remote_start_common(ud->kcov_handle);
>                 vhci_rx_pdu(ud);
> -               usbip_kcov_remote_stop();
> +               kcov_remote_stop();
>         }
>
>         return 0;
> diff --git a/drivers/usb/usbip/vhci_sysfs.c b/drivers/usb/usbip/vhci_sysfs.c
> index 5bc8c47788d4..b98d14c43d13 100644
> --- a/drivers/usb/usbip/vhci_sysfs.c
> +++ b/drivers/usb/usbip/vhci_sysfs.c
> @@ -425,7 +425,7 @@ static ssize_t attach_store(struct device *dev, struct device_attribute *attr,
>         vdev->ud.tcp_rx     = tcp_rx;
>         vdev->ud.tcp_tx     = tcp_tx;
>         vdev->ud.status     = VDEV_ST_NOTASSIGNED;
> -       usbip_kcov_handle_init(&vdev->ud);
> +       vdev->ud.kcov_handle = kcov_common_handle();
>
>         spin_unlock(&vdev->ud.lock);
>         spin_unlock_irqrestore(&vhci->lock, flags);
> diff --git a/drivers/vhost/vhost.h b/drivers/vhost/vhost.h
> index 4fe99765c5c7..0192ade6e749 100644
> --- a/drivers/vhost/vhost.h
> +++ b/drivers/vhost/vhost.h
> @@ -44,7 +44,7 @@ struct vhost_worker {
>         /* Used to serialize device wide flushing with worker swapping. */
>         struct mutex            mutex;
>         struct llist_head       work_list;
> -       u64                     kcov_handle;
> +       struct kcov_common_handle_id kcov_handle;
>         u32                     id;
>         int                     attachment_cnt;
>         bool                    killed;
> diff --git a/include/linux/kcov.h b/include/linux/kcov.h
> index 0143358874b0..cdb72b3859d8 100644
> --- a/include/linux/kcov.h
> +++ b/include/linux/kcov.h
> @@ -43,11 +43,11 @@ do {                                                \
>  /* See Documentation/dev-tools/kcov.rst for usage details. */
>  void kcov_remote_start(u64 handle);
>  void kcov_remote_stop(void);
> -u64 kcov_common_handle(void);
> +struct kcov_common_handle_id kcov_common_handle(void);
>
> -static inline void kcov_remote_start_common(u64 id)
> +static inline void kcov_remote_start_common(struct kcov_common_handle_id id)
>  {
> -       kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id));
> +       kcov_remote_start(kcov_remote_handle(KCOV_SUBSYSTEM_COMMON, id.val));
>  }
>
>  static inline void kcov_remote_start_usb(u64 id)
> @@ -99,11 +99,11 @@ static inline void kcov_prepare_switch(struct task_struct *t) {}
>  static inline void kcov_finish_switch(struct task_struct *t) {}
>  static inline void kcov_remote_start(u64 handle) {}
>  static inline void kcov_remote_stop(void) {}
> -static inline u64 kcov_common_handle(void)
> +static inline struct kcov_common_handle_id kcov_common_handle(void)
>  {
> -       return 0;
> +       return (struct kcov_common_handle_id){};
>  }
> -static inline void kcov_remote_start_common(u64 id) {}
> +static inline void kcov_remote_start_common(struct kcov_common_handle_id id) {}
>  static inline void kcov_remote_start_usb(u64 id) {}
>  static inline void kcov_remote_start_usb_softirq(u64 id) {}
>  static inline void kcov_remote_stop_softirq(void) {}
> diff --git a/include/linux/skbuff.h b/include/linux/skbuff.h
> index 2bcf78a4de7b..a3fe418f7ced 100644
> --- a/include/linux/skbuff.h
> +++ b/include/linux/skbuff.h
> @@ -1082,9 +1082,7 @@ struct sk_buff {
>         __u16                   network_header;
>         __u16                   mac_header;
>
> -#ifdef CONFIG_KCOV
> -       u64                     kcov_handle;
> -#endif
> +       struct kcov_common_handle_id kcov_handle;
>
>         ); /* end headers group */
>
> @@ -5437,20 +5435,14 @@ static inline void skb_reset_csum_not_inet(struct sk_buff *skb)
>  }
>
>  static inline void skb_set_kcov_handle(struct sk_buff *skb,
> -                                      const u64 kcov_handle)
> +                                      struct kcov_common_handle_id kcov_handle)
>  {
> -#ifdef CONFIG_KCOV
>         skb->kcov_handle = kcov_handle;
> -#endif
>  }
>
> -static inline u64 skb_get_kcov_handle(struct sk_buff *skb)
> +static inline struct kcov_common_handle_id skb_get_kcov_handle(struct sk_buff *skb)
>  {
> -#ifdef CONFIG_KCOV
>         return skb->kcov_handle;
> -#else
> -       return 0;
> -#endif
>  }
>
>  static inline void skb_mark_for_recycle(struct sk_buff *skb)
> diff --git a/include/linux/types.h b/include/linux/types.h
> index 608050dbca6a..93166b0b0617 100644
> --- a/include/linux/types.h
> +++ b/include/linux/types.h
> @@ -224,6 +224,12 @@ struct ustat {
>         char                    f_fpack[6];
>  };
>
> +struct kcov_common_handle_id {
> +#ifdef CONFIG_KCOV
> +       u64 val;
> +#endif
> +};
> +
>  /**
>   * struct callback_head - callback structure for use with RCU and task_work
>   * @next: next update requests in a list
> diff --git a/kernel/kcov.c b/kernel/kcov.c
> index 0b369e88c7c9..a43e33a28adb 100644
> --- a/kernel/kcov.c
> +++ b/kernel/kcov.c
> @@ -1083,11 +1083,11 @@ void kcov_remote_stop(void)
>  EXPORT_SYMBOL(kcov_remote_stop);
>
>  /* See the comment before kcov_remote_start() for usage details. */
> -u64 kcov_common_handle(void)
> +struct kcov_common_handle_id kcov_common_handle(void)
>  {
>         if (!in_task())
> -               return 0;
> -       return current->kcov_handle;
> +               return (struct kcov_common_handle_id){ .val = 0 };
> +       return (struct kcov_common_handle_id){ .val = current->kcov_handle };
>  }
>  EXPORT_SYMBOL(kcov_common_handle);
>
>
> ---
> base-commit: 57b8e2d666a31fa201432d58f5fe3469a0dd83ba
> change-id: 20260430-kcov-refactor-common-handle-25178495b2eb
>
> --
> Jann Horn <jannh@xxxxxxxxxx>
>