From: Daniel Borkmann <dborkman@redhat.com>
To: Alexei Starovoitov <ast@plumgrid.com>
Cc: "David S. Miller" <davem@davemloft.net>,
Ingo Molnar <mingo@kernel.org>,
Andy Lutomirski <luto@amacapital.net>,
Hannes Frederic Sowa <hannes@stressinduktion.org>,
Eric Dumazet <edumazet@google.com>,
linux-api@vger.kernel.org, netdev@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next 3/7] bpf: add array type of eBPF maps
Date: Tue, 04 Nov 2014 10:58:33 +0100 [thread overview]
Message-ID: <5458A349.5020401@redhat.com> (raw)
In-Reply-To: <1415069656-14138-4-git-send-email-ast@plumgrid.com>
On 11/04/2014 03:54 AM, Alexei Starovoitov wrote:
> add new map type BPF_MAP_TYPE_ARRAY and its implementation
>
> - optimized for fastest possible lookup()
> . in the future verifier/JIT may recognize lookup() with constant key
> and optimize it into constant pointer. Can optimize non-constant
> key into direct pointer arithmetic as well, since pointers and
> value_size are constant for the life of the eBPF program.
> In other words array_map_lookup_elem() may be 'inlined' by verifier/JIT
> while preserving concurrent access to this map from user space
>
> - two main use cases for array type:
> . 'global' eBPF variables: array of 1 element with key=0 and value is a
> collection of 'global' variables which programs can use to keep the state
> between events
> . aggregation of tracing events into fixed set of buckets
>
> - all array elements pre-allocated and zero initialized at init time
>
> - key as an index in array and can only be 4 byte
>
> - map_delete_elem() returns EINVAL, since elements cannot be deleted
>
> - map_update_elem() replaces elements in an non-atomic way
> (for atomic updates hashtable type should be used instead)
>
> Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
...
> +/* Called from syscall or from eBPF program */
> +static int array_map_update_elem(struct bpf_map *map, void *key, void *value,
> + u64 map_flags)
> +{
> + struct bpf_array *array = container_of(map, struct bpf_array, map);
> + u32 index = *(u32 *)key;
> +
> + if (map_flags > BPF_MAP_UPDATE_ONLY)
> + /* unknown flags */
> + return -EINVAL;
> +
> + if (map_flags == BPF_MAP_CREATE_ONLY)
> + return -EINVAL;
> +
> + if (index >= array->map.max_entries)
> + /* all elements were pre-allocated, cannot insert a new one */
> + return -E2BIG;
> +
> + memcpy(array->value + array->elem_size * index, value, array->elem_size);
What would protect this from concurrent updates?
> + return 0;
> +}
next prev parent reply other threads:[~2014-11-04 9:58 UTC|newest]
Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-11-04 2:54 [PATCH net-next 0/7] implementation of eBPF maps Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 1/7] bpf: add 'flags' attribute to BPF_MAP_UPDATE_ELEM command Alexei Starovoitov
2014-11-04 9:25 ` Daniel Borkmann
2014-11-04 23:04 ` Alexei Starovoitov
2014-11-05 14:57 ` Daniel Borkmann
2014-11-06 17:39 ` Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 2/7] bpf: add hashtable type of eBPF maps Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 3/7] bpf: add array " Alexei Starovoitov
2014-11-04 9:58 ` Daniel Borkmann [this message]
2014-11-04 23:14 ` Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 4/7] bpf: fix BPF_MAP_LOOKUP_ELEM command return code Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 5/7] bpf: add a testsuite for eBPF maps Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 6/7] bpf: allow eBPF programs to use maps Alexei Starovoitov
2014-11-04 9:50 ` Daniel Borkmann
2014-11-04 23:08 ` Alexei Starovoitov
2014-11-04 2:54 ` [PATCH net-next 7/7] bpf: remove test map scaffolding and use proper types Alexei Starovoitov
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