Re: [RFC PATCH net-next] net/sched: introduce pretty printers for Qdiscs

[Pedro Tammela <pctammela@mojatatu.com>]

On 02/06/2023 13:29, Vladimir Oltean wrote:
> Sometimes when debugging Qdiscs it may be confusing to know exactly what
> you're looking at, especially since they're hierarchical. Pretty printing
> the handle, parent handle and netdev is a bit cumbersome, so this patch
> proposes a set of wrappers around __qdisc_printk() which are heavily
> inspired from __net_printk().

Probably worth mentioning drgn 
(https://drgn.readthedocs.io/en/latest/user_guide.html)
I've picked it up recently after Peilin mentioned it and it's quite helpful.

> 
> It is assumed that these printers will be more useful for untalented
> kernel hackers such as myself rather than to the overall quality of the
> code, since Qdiscs rarely print stuff to the kernel log by design (and
> where they do, maybe that should be reconsidered in the first place).
> 
> A single demo conversion has been made, there is room for more if the
> idea is appreciated.
> 
> Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
> ---
>   include/net/sch_debug.h | 45 +++++++++++++++++++++
>   net/sched/Makefile      |  2 +-
>   net/sched/sch_api.c     |  4 +-
>   net/sched/sch_debug.c   | 86 +++++++++++++++++++++++++++++++++++++++++
>   4 files changed, 134 insertions(+), 3 deletions(-)
>   create mode 100644 include/net/sch_debug.h
>   create mode 100644 net/sched/sch_debug.c
> 
> diff --git a/include/net/sch_debug.h b/include/net/sch_debug.h
> new file mode 100644
> index 000000000000..032de4710671
> --- /dev/null
> +++ b/include/net/sch_debug.h
> @@ -0,0 +1,45 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +#ifndef __NET_SCHED_DEBUG_H
> +#define __NET_SCHED_DEBUG_H
> +
> +#include <linux/bug.h>
> +#include <linux/kern_levels.h>
> +
> +struct Qdisc;
> +
> +__printf(3, 4) __cold
> +void qdisc_printk(const char *level, const struct Qdisc *sch,
> +		  const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_emerg(const struct Qdisc *sch, const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_alert(const struct Qdisc *sch, const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_crit(const struct Qdisc *sch, const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_err(const struct Qdisc *sch, const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_warn(const struct Qdisc *sch, const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_notice(const struct Qdisc *sch, const char *format, ...);
> +__printf(2, 3) __cold
> +void qdisc_info(const struct Qdisc *sch, const char *format, ...);
> +
> +#if defined(CONFIG_DYNAMIC_DEBUG) || \
> +	(defined(CONFIG_DYNAMIC_DEBUG_CORE) && defined(DYNAMIC_DEBUG_MODULE))
> +#define qdisc_dbg(__sch, format, args...)			\
> +do {								\
> +	dynamic_qdisc_dbg(__sch, format, ##args);		\
> +} while (0)
> +#elif defined(DEBUG)
> +#define qdisc_dbg(__sch, format, args...)			\
> +	qdisc_printk(KERN_DEBUG, __sch, format, ##args)
> +#else
> +#define qdisc_dbg(__sch, format, args...)			\
> +({								\
> +	if (0)							\
> +		qdisc_printk(KERN_DEBUG, __sch, format, ##args); \
> +})
> +#endif
> +
> +#endif
> diff --git a/net/sched/Makefile b/net/sched/Makefile
> index b5fd49641d91..ab13bf7db283 100644
> --- a/net/sched/Makefile
> +++ b/net/sched/Makefile
> @@ -6,7 +6,7 @@
>   obj-y	:= sch_generic.o sch_mq.o
>   
>   obj-$(CONFIG_INET)		+= sch_frag.o
> -obj-$(CONFIG_NET_SCHED)		+= sch_api.o sch_blackhole.o
> +obj-$(CONFIG_NET_SCHED)		+= sch_api.o sch_blackhole.o sch_debug.o
>   obj-$(CONFIG_NET_CLS)		+= cls_api.o
>   obj-$(CONFIG_NET_CLS_ACT)	+= act_api.o
>   obj-$(CONFIG_NET_ACT_POLICE)	+= act_police.o
> diff --git a/net/sched/sch_api.c b/net/sched/sch_api.c
> index fdb8f429333d..a6bfe2e40f89 100644
> --- a/net/sched/sch_api.c
> +++ b/net/sched/sch_api.c
> @@ -31,6 +31,7 @@
>   #include <net/netlink.h>
>   #include <net/pkt_sched.h>
>   #include <net/pkt_cls.h>
> +#include <net/sch_debug.h>
>   #include <net/tc_wrapper.h>
>   
>   #include <trace/events/qdisc.h>
> @@ -597,8 +598,7 @@ EXPORT_SYMBOL(__qdisc_calculate_pkt_len);
>   void qdisc_warn_nonwc(const char *txt, struct Qdisc *qdisc)
>   {
>   	if (!(qdisc->flags & TCQ_F_WARN_NONWC)) {
> -		pr_warn("%s: %s qdisc %X: is non-work-conserving?\n",
> -			txt, qdisc->ops->id, qdisc->handle >> 16);
> +		qdisc_warn(qdisc, "%s: qdisc is non-work-conserving?\n", txt);

Looks much better

>   		qdisc->flags |= TCQ_F_WARN_NONWC;
>   	}
>   }
> diff --git a/net/sched/sch_debug.c b/net/sched/sch_debug.c
> new file mode 100644
> index 000000000000..1f47dac88c6e
> --- /dev/null
> +++ b/net/sched/sch_debug.c
> @@ -0,0 +1,86 @@ > +#include <linux/pkt_sched.h>
> +#include <net/sch_generic.h>
> +#include <net/sch_debug.h>
> +
> +static void qdisc_handle_str(u32 handle, char *str)
> +{
> +	if (handle == TC_H_ROOT) {
> +		sprintf(str, "root");
> +		return;
> +	} else if (handle == TC_H_INGRESS) {
> +		sprintf(str, "ingress");
> +		return;
> +	} else {
> +		sprintf(str, "%x:%x", TC_H_MAJ(handle) >> 16, TC_H_MIN(handle));
> +		return;
> +	}

nit: Did you consider a switch?

> +}
> +
> +static void __qdisc_printk(const char *level, const struct Qdisc *sch,
> +			   struct va_format *vaf)
> +{
> +	struct net_device *dev = qdisc_dev(sch);
> +	char handle_str[10], parent_str[10];
> +
> +	qdisc_handle_str(sch->handle, handle_str);
> +	qdisc_handle_str(sch->parent, parent_str);
> +
> +	if (dev && dev->dev.parent) {
> +		dev_printk_emit(level[1] - '0',
> +				dev->dev.parent,
> +				"%s %s %s%s %s %s parent %s: %pV",
> +				dev_driver_string(dev->dev.parent),
> +				dev_name(dev->dev.parent),
> +				netdev_name(dev), netdev_reg_state(dev),
> +				sch->ops->id, handle_str, parent_str, vaf);
> +	} else if (dev) {
> +		printk("%s%s%s %s %s parent %s: %pV",
> +		       level, netdev_name(dev), netdev_reg_state(dev),
> +		       sch->ops->id, handle_str, parent_str, vaf);
> +	} else {
> +		printk("%s(NULL net_device) %s %s parent %s: %pV", level,
> +		       sch->ops->id, handle_str, parent_str, vaf);
> +	}
> +}
> +
> +void qdisc_printk(const char *level, const struct Qdisc *sch,
> +		  const char *format, ...)
> +{
> +	struct va_format vaf;
> +	va_list args;
> +
> +	va_start(args, format);
> +
> +	vaf.fmt = format;
> +	vaf.va = &args;
> +
> +	__qdisc_printk(level, sch, &vaf);
> +
> +	va_end(args);
> +}
> +EXPORT_SYMBOL(qdisc_printk);
> +
> +#define define_qdisc_printk_level(func, level)			\
> +void func(const struct Qdisc *sch, const char *fmt, ...)	\
> +{								\
> +	struct va_format vaf;					\
> +	va_list args;						\
> +								\
> +	va_start(args, fmt);					\
> +								\
> +	vaf.fmt = fmt;						\
> +	vaf.va = &args;						\
> +								\
> +	__qdisc_printk(level, sch, &vaf);			\
> +								\
> +	va_end(args);						\
> +}								\
> +EXPORT_SYMBOL(func);
> +
> +define_qdisc_printk_level(qdisc_emerg, KERN_EMERG);
> +define_qdisc_printk_level(qdisc_alert, KERN_ALERT);
> +define_qdisc_printk_level(qdisc_crit, KERN_CRIT);
> +define_qdisc_printk_level(qdisc_err, KERN_ERR);
> +define_qdisc_printk_level(qdisc_warn, KERN_WARNING);
> +define_qdisc_printk_level(qdisc_notice, KERN_NOTICE);
> +define_qdisc_printk_level(qdisc_info, KERN_INFO);