netdev - Re: [PATCH bpf-next 2/3] bpf: add bpffs pretty print for cgroup local storage maps

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Date:   Mon, 10 Dec 2018 22:46:04 +0000
From:   Roman Gushchin <guro@...com>
To:     Yonghong Song <yhs@...com>
CC:     Roman Gushchin <guroan@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Kernel Team <Kernel-team@...com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Alexei Starovoitov" <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>
Subject: Re: [PATCH bpf-next 2/3] bpf: add bpffs pretty print for cgroup local
 storage maps

On Fri, Dec 07, 2018 at 07:37:35PM -0800, Yonghong Song wrote:
> 
> 
> On 12/7/18 4:53 PM, Roman Gushchin wrote:
> > Implement bpffs pretty printing for cgroup local storage maps
> > (both shared and per-cpu).
> > Output example (captured for tools/testing/selftests/bpf/netcnt_prog.c):
> > 
> > Shared:
> >    $ cat /sys/fs/bpf/map_2
> >    # WARNING!! The output is for debug purpose only
> >    # WARNING!! The output format will change
> >    {4294968594,1}: {9999,1039896}
> > 
> > Per-cpu:
> >    $ cat /sys/fs/bpf/map_1
> >    # WARNING!! The output is for debug purpose only
> >    # WARNING!! The output format will change
> >    {4294968594,1}: {
> >    	cpu0: {0,0,0,0,0}
> >    	cpu1: {0,0,0,0,0}
> >    	cpu2: {1,104,0,0,0}
> >    	cpu3: {0,0,0,0,0}
> >    }
> > 
> > Signed-off-by: Roman Gushchin <guro@...com>
> > Cc: Alexei Starovoitov <ast@...nel.org>
> > Cc: Daniel Borkmann <daniel@...earbox.net>
> > ---
> >   include/linux/btf.h        | 10 +++++
> >   kernel/bpf/local_storage.c | 90 +++++++++++++++++++++++++++++++++++++-
> >   2 files changed, 99 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/linux/btf.h b/include/linux/btf.h
> > index 8c2199b5d250..ac67bc4cbfd9 100644
> > --- a/include/linux/btf.h
> > +++ b/include/linux/btf.h
> > @@ -5,6 +5,7 @@
> >   #define _LINUX_BTF_H 1
> >   
> >   #include <linux/types.h>
> > +#include <uapi/linux/btf.h>
> >   
> >   struct btf;
> >   struct btf_type;
> > @@ -63,4 +64,13 @@ static inline const char *btf_name_by_offset(const struct btf *btf,
> >   }
> >   #endif
> >   
> > +static inline const struct btf_type *btf_orig_type(const struct btf *btf,
> > +						   const struct btf_type *t)
> > +{
> > +	while (t && BTF_INFO_KIND(t->info) == BTF_KIND_TYPEDEF)
> > +		t = btf_type_by_id(btf, t->type);
> technically, type modifier "const" and "volatile" can apply to member 
> type as well. But these modifiers really don't make sense here.
> Could you add a comment here to mention that they will be treated
> as an error since such a programming is not really recommended?

Switched over to btf_type_id_size() based on Martin's suggestion.

> 
> > +
> > +	return t;
> > +}
> > +
> >   #endif
> > diff --git a/kernel/bpf/local_storage.c b/kernel/bpf/local_storage.c
> > index b65017dead44..7b51fe1aba3c 100644
> > --- a/kernel/bpf/local_storage.c
> > +++ b/kernel/bpf/local_storage.c
> > @@ -1,11 +1,13 @@
> >   //SPDX-License-Identifier: GPL-2.0
> >   #include <linux/bpf-cgroup.h>
> >   #include <linux/bpf.h>
> > +#include <linux/btf.h>
> >   #include <linux/bug.h>
> >   #include <linux/filter.h>
> >   #include <linux/mm.h>
> >   #include <linux/rbtree.h>
> >   #include <linux/slab.h>
> > +#include <uapi/linux/btf.h>
> >   
> >   DEFINE_PER_CPU(struct bpf_cgroup_storage*, bpf_cgroup_storage[MAX_BPF_CGROUP_STORAGE_TYPE]);
> >   
> > @@ -308,6 +310,91 @@ static int cgroup_storage_delete_elem(struct bpf_map *map, void *key)
> >   	return -EINVAL;
> >   }
> >   
> > +static int cgroup_storage_check_btf(const struct bpf_map *map,
> > +				    const struct btf *btf,
> > +				    const struct btf_type *key_type,
> > +				    const struct btf_type *value_type)
> > +{
> > +	const struct btf_type *st, *t;
> > +	struct btf_member *m;
> > +
> > +	/* Key is expected to be of struct bpf_cgroup_storage_key type,
> > +	 * which is:
> > +	 * struct bpf_cgroup_storage_key {
> > +	 *	__u64	cgroup_inode_id;
> > +	 *	__u32	attach_type;
> > +	 * };
> > +	 */
> > +
> > +	/*
> > +	 * Key_type must be a structure (or a typedef of a structure) with
> > +	 * two members.
> > +	 */
> > +	st = btf_orig_type(btf, key_type);
> > +	if (BTF_INFO_KIND(st->info) != BTF_KIND_STRUCT ||
> > +	    BTF_INFO_VLEN(st->info) != 2)
> > +		return -EINVAL;
> > +
> > +	/*
> > +	 * The first field must be a 64 bit integer at 0 offset.
> > +	 */
> > +	m = (struct btf_member *)(st + 1);
> > +	t = btf_orig_type(btf, btf_type_by_id(btf, m->type));
> > +	if (!t || BTF_INFO_KIND(t->info) != BTF_KIND_INT || m->offset ||
> > +	    t->size !=
> > +	    FIELD_SIZEOF(struct bpf_cgroup_storage_key, cgroup_inode_id))
> > +		return -EINVAL;
> 
> We should not use t->size here. The "t->size" is the type size, and the
> real number of bits held by the member is BTF_INT_BITS(...) with the 
> argument of the u32 int value after "t".
> 
> > +
> > +	/*
> > +	 * The second field must be a 32 bit integer at 0 offset.
> > +	 */
> > +	m = m + 1;
> > +	t = btf_orig_type(btf, btf_type_by_id(btf, m->type));
> > +	if (!t || BTF_INFO_KIND(t->info) != BTF_KIND_INT ||
> > +	    m->offset != offsetof(struct bpf_cgroup_storage_key, attach_type) *
> > +	    BITS_PER_BYTE || t->size !=
> > +	    FIELD_SIZEOF(struct bpf_cgroup_storage_key, attach_type))
> > +		return -EINVAL;
> 
> The same is here. t->size should not be used.
> BTF_INT_BITS(...) should be used.

Fixed in v2, which I'll send soon.

Thank you for the review!