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Date: Fri, 26 Apr 2019 18:49:43 +0000
From: Yonghong Song <yhs@...com>
To: Martin Lau <kafai@...com>
CC: "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
Alexei Starovoitov <ast@...com>,
Andrii Nakryiko <andriin@...com>,
Daniel Borkmann <daniel@...earbox.net>,
John Fastabend <john.fastabend@...il.com>,
Kernel Team <Kernel-team@...com>
Subject: Re: [PATCH v3 bpf-next 3/6] bpf: Support BPF_MAP_TYPE_SK_STORAGE in
bpf map probing
On 4/26/19 11:21 AM, Martin Lau wrote:
> On Fri, Apr 26, 2019 at 10:50:29AM -0700, Yonghong Song wrote:
>>
>>
>> On 4/26/19 10:11 AM, Martin KaFai Lau wrote:
>>> This patch supports probing for the new BPF_MAP_TYPE_SK_STORAGE.
>>> BPF_MAP_TYPE_SK_STORAGE enforces BTF usage, so the new probe
>>> requires to create and load a BTF also.
>>>
>>> Signed-off-by: Martin KaFai Lau <kafai@...com>
>>> ---
>>> tools/bpf/bpftool/map.c | 1 +
>>> tools/lib/bpf/libbpf_probes.c | 74 ++++++++++++++++++++++++++++++++++-
>>> 2 files changed, 74 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
>>> index 10b6c9d3e525..693ab3da37de 100644
>>> --- a/tools/bpf/bpftool/map.c
>>> +++ b/tools/bpf/bpftool/map.c
>>> @@ -46,6 +46,7 @@ const char * const map_type_name[] = {
>>> [BPF_MAP_TYPE_PERCPU_CGROUP_STORAGE] = "percpu_cgroup_storage",
>>> [BPF_MAP_TYPE_QUEUE] = "queue",
>>> [BPF_MAP_TYPE_STACK] = "stack",
>>> + [BPF_MAP_TYPE_SK_STORAGE] = "sk_storage",
>>> };
>>>
>>> const size_t map_type_name_size = ARRAY_SIZE(map_type_name);
>>> diff --git a/tools/lib/bpf/libbpf_probes.c b/tools/lib/bpf/libbpf_probes.c
>>> index 0f25541632e3..2e26ddb005e4 100644
>>> --- a/tools/lib/bpf/libbpf_probes.c
>>> +++ b/tools/lib/bpf/libbpf_probes.c
>>> @@ -9,6 +9,7 @@
>>> #include <net/if.h>
>>> #include <sys/utsname.h>
>>>
>>> +#include <linux/btf.h>
>>> #include <linux/filter.h>
>>> #include <linux/kernel.h>
>>>
>>> @@ -130,11 +131,65 @@ bool bpf_probe_prog_type(enum bpf_prog_type prog_type, __u32 ifindex)
>>> return errno != EINVAL && errno != EOPNOTSUPP;
>>> }
>>>
>>> +static int load_btf(void)
>>> +{
>>> +#define BTF_INFO_ENC(kind, kind_flag, vlen) \
>>> + ((!!(kind_flag) << 31) | ((kind) << 24) | ((vlen) & BTF_MAX_VLEN))
>>> +#define BTF_TYPE_ENC(name, info, size_or_type) \
>>> + (name), (info), (size_or_type)
>>> +#define BTF_INT_ENC(encoding, bits_offset, nr_bits) \
>>> + ((encoding) << 24 | (bits_offset) << 16 | (nr_bits))
>>> +#define BTF_TYPE_INT_ENC(name, encoding, bits_offset, bits, sz) \
>>> + BTF_TYPE_ENC(name, BTF_INFO_ENC(BTF_KIND_INT, 0, 0), sz), \
>>> + BTF_INT_ENC(encoding, bits_offset, bits)
>>> +#define BTF_MEMBER_ENC(name, type, bits_offset) \
>>> + (name), (type), (bits_offset)
>>> +
>>> + const char btf_str_sec[] = "\0bpf_spin_lock\0val\0cnt\0l";
>>> + /* struct bpf_spin_lock {
>>> + * int val;
>>> + * };
>>> + * struct val {
>>> + * int cnt;
>>> + * struct bpf_spin_lock l;
>>> + * };
>>> + */
>>> + __u32 btf_raw_types[] = {
>>> + /* int */
>>> + BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), /* [1] */
>>> + /* struct bpf_spin_lock */ /* [2] */
>>> + BTF_TYPE_ENC(1, BTF_INFO_ENC(BTF_KIND_STRUCT, 0, 1), 4),
>>> + BTF_MEMBER_ENC(15, 1, 0), /* int val; */
>>> + /* struct val */ /* [3] */
>>> + BTF_TYPE_ENC(15, BTF_INFO_ENC(BTF_KIND_STRUCT, 0, 2), 8),
>>> + BTF_MEMBER_ENC(19, 1, 0), /* int cnt; */
>>> + BTF_MEMBER_ENC(23, 2, 32),/* struct bpf_spin_lock l; */
>>> + };
>>> + struct btf_header btf_hdr = {
>>> + .magic = BTF_MAGIC,
>>> + .version = BTF_VERSION,
>>> + .hdr_len = sizeof(struct btf_header),
>>> + .type_len = sizeof(btf_raw_types),
>>> + .str_off = sizeof(btf_raw_types),
>>> + .str_len = sizeof(btf_str_sec),
>>> + };
>>> + __u8 raw_btf[sizeof(struct btf_header) + sizeof(btf_raw_types) +
>>> + sizeof(btf_str_sec)];
>>> +
>>> + memcpy(raw_btf, &btf_hdr, sizeof(btf_hdr));
>>> + memcpy(raw_btf + sizeof(btf_hdr), btf_raw_types, sizeof(btf_raw_types));
>>> + memcpy(raw_btf + sizeof(btf_hdr) + sizeof(btf_raw_types),
>>> + btf_str_sec, sizeof(btf_str_sec));
>>> +
>>> + return bpf_load_btf(raw_btf, sizeof(raw_btf), 0, 0, 0);
>>> +}
>>
>> In the future, different map types could want to test different type
>> configurations. Maybe btf_raw_types and btf_str_sec could be provided
>> as a parameter for load_btf()?
> I think it will be cleaner to keep one btf_raw_types[].
> Other types can be added to the same btf_raw_types[] later instead of
> redefining int/long/unsigned...etc. The bpf_probe_map_type() can
> point the btf_key_type_id and btf_value_type_id to different type_id.
>
> It can be revisited if it needs to probe some newly introduced BTF type
> (in the type section) later which I think should be very rare.
Fair enough. We can revisit later once there is a need for probing btf
for a different purpose.
>
>>
>>> +
>>> bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex)
>>> {
>>> int key_size, value_size, max_entries, map_flags;
>>> + __u32 btf_key_type_id = 0, btf_value_type_id = 0;
>>> struct bpf_create_map_attr attr = {};
>>> - int fd = -1, fd_inner;
>>> + int fd = -1, btf_fd = -1, fd_inner;
>>>
>>> key_size = sizeof(__u32);
>>> value_size = sizeof(__u32);
>>> @@ -160,6 +215,16 @@ bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex)
>>> case BPF_MAP_TYPE_STACK:
>>> key_size = 0;
>>> break;
>>> + case BPF_MAP_TYPE_SK_STORAGE:
>>> + btf_key_type_id = 1;
>>> + btf_value_type_id = 3;
>>> + value_size = 8;
>>> + max_entries = 0;
>>> + map_flags = BPF_F_NO_PREALLOC;
>>> + btf_fd = load_btf();
>>> + if (btf_fd < 0)
>>> + return false;
>>> + break;
>>> case BPF_MAP_TYPE_UNSPEC:
>>> case BPF_MAP_TYPE_HASH:
>>> case BPF_MAP_TYPE_ARRAY:
>>> @@ -205,11 +270,18 @@ bool bpf_probe_map_type(enum bpf_map_type map_type, __u32 ifindex)
>>> attr.max_entries = max_entries;
>>> attr.map_flags = map_flags;
>>> attr.map_ifindex = ifindex;
>>> + if (btf_fd >= 0) {
>>> + attr.btf_fd = btf_fd;
>>> + attr.btf_key_type_id = btf_key_type_id;
>>> + attr.btf_value_type_id = btf_value_type_id;
>>> + }
>>>
>>> fd = bpf_create_map_xattr(&attr);
>>> }
>>> if (fd >= 0)
>>> close(fd);
>>> + if (btf_fd >= 0)
>>> + close(btf_fd);
>>>
>>> return fd >= 0;
>>> }
>>>
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