* [PATCH v2 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY @ 2021-11-23 16:24 Dave Tucker 2021-11-23 16:24 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker 0 siblings, 1 reply; 6+ messages in thread From: Dave Tucker @ 2021-11-23 16:24 UTC (permalink / raw) To: bpf Cc: corbet, ast, daniel, andrii, kafai, songliubraving, john.fastabend, kpsingh, linux-doc, Dave Tucker This series is the beginning of my attempt to improve the BPF map and program type documentation. It expands the template from map_cgroup_storage to include the kernel version it was introduced. I then used this template to document BPF_MAP_TYPE_ARRAY and BPF_MAP_TYPE_PERCPU_ARRAY v1->v2: - point to selftests for functional examples - update examples to follow kernel style - add docs for BPF_F_MMAPABLE Dave Tucker (2): bpf, docs: add kernel version to map_cgroup_storage bpf, docs: document BPF_MAP_TYPE_ARRAY Documentation/bpf/map_array.rst | 172 +++++++++++++++++++++++ Documentation/bpf/map_cgroup_storage.rst | 2 + 2 files changed, 174 insertions(+) create mode 100644 Documentation/bpf/map_array.rst -- 2.33.1 ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage 2021-11-23 16:24 [PATCH v2 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY Dave Tucker @ 2021-11-23 16:24 ` Dave Tucker 2021-11-23 16:24 ` [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-11-27 1:53 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Song Liu 0 siblings, 2 replies; 6+ messages in thread From: Dave Tucker @ 2021-11-23 16:24 UTC (permalink / raw) To: bpf Cc: corbet, ast, daniel, andrii, kafai, songliubraving, john.fastabend, kpsingh, linux-doc, Dave Tucker This adds the version at which this map became available to use in the documentation Signed-off-by: Dave Tucker <dave@dtucker.co.uk> --- Documentation/bpf/map_cgroup_storage.rst | 2 ++ 1 file changed, 2 insertions(+) diff --git a/Documentation/bpf/map_cgroup_storage.rst b/Documentation/bpf/map_cgroup_storage.rst index cab9543017bf..b626cb068846 100644 --- a/Documentation/bpf/map_cgroup_storage.rst +++ b/Documentation/bpf/map_cgroup_storage.rst @@ -5,6 +5,8 @@ BPF_MAP_TYPE_CGROUP_STORAGE =========================== +.. note:: Introduced in Kernel version 4.19 + The ``BPF_MAP_TYPE_CGROUP_STORAGE`` map type represents a local fix-sized storage. It is only available with ``CONFIG_CGROUP_BPF``, and to programs that attach to cgroups; the programs are made available by the same Kconfig. The -- 2.33.1 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-11-23 16:24 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker @ 2021-11-23 16:24 ` Dave Tucker 2021-11-27 2:05 ` Song Liu 2021-12-02 20:08 ` Andrii Nakryiko 2021-11-27 1:53 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Song Liu 1 sibling, 2 replies; 6+ messages in thread From: Dave Tucker @ 2021-11-23 16:24 UTC (permalink / raw) To: bpf Cc: corbet, ast, daniel, andrii, kafai, songliubraving, john.fastabend, kpsingh, linux-doc, Dave Tucker This commit adds documentation for the BPF_MAP_TYPE_ARRAY including kernel version introduced, usage and examples. It also documents BPF_MAP_TYPE_PERCPU_ARRAY since this is similar. Signed-off-by: Dave Tucker <dave@dtucker.co.uk> --- Documentation/bpf/map_array.rst | 172 ++++++++++++++++++++++++++++++++ 1 file changed, 172 insertions(+) create mode 100644 Documentation/bpf/map_array.rst diff --git a/Documentation/bpf/map_array.rst b/Documentation/bpf/map_array.rst new file mode 100644 index 000000000000..8ba05ba5d4ee --- /dev/null +++ b/Documentation/bpf/map_array.rst @@ -0,0 +1,172 @@ +.. SPDX-License-Identifier: GPL-2.0-only +.. Copyright (C) 2021 Red Hat, Inc. + +================================================ +BPF_MAP_TYPE_ARRAY and BPF_MAP_TYPE_PERCPU_ARRAY +================================================ + +.. note:: ``BPF_MAP_TYPE_ARRAY`` was introduced in Kernel version 3.19 and ``BPF_MAP_TYPE_PERCPU_ARRAY`` in version 4.6 + +``BPF_MAP_TYPE_ARRAY`` and ``BPF_MAP_TYPE_PERCPU_ARRAY`` provide generic array storage. +The key type is an unsigned 32-bit integer (4 bytes) and the map is of constant size. +All array elements are pre-allocated and zero initialized when created. +``BPF_MAP_TYPE_PERCPU_ARRAY`` uses a different memory region for each CPU whereas +``BPF_MAP_TYPE_ARRAY`` uses the same memory region. +The maximum size of an array, defined in max_entries, is limited to 2^32. +The value stored can be of any size, however, small values will be rounded up to 8 bytes. + +Since Kernel 5.4, memory mapping may be enabled for ``BPF_MAP_TYPE_ARRAY`` by setting the flag ``BPF_F_MMAPABLE``. +The map definition is page-aligned and starts on the first page. +Sufficient page-sized and page-aligned blocks of memory are allocated to store all array values, starting on the second page, +which in some cases will result in over-allocation of memory. The benefit of using this is increased performance and +ease of use since userspace programs would not be required to use helper functions to access and mutate data. + +Usage +===== + +Array elements can be retrieved using the ``bpf_map_lookup_elem()`` helper. +This helper returns a pointer into the array element, so to avoid data races with userspace reading the value, +the user must use primitives like ``__sync_fetch_and_add()`` when updating the value in-place. +Access from userspace uses the libbpf API of the same name. + +Array elements can also be added using the ``bpf_map_update_elem()`` helper or libbpf API. + +Since the array is of constant size, ``bpf_map_delete_elem()`` is not supported. +To clear an array element, you may use ``bpf_map_update_eleme()`` to insert a zero value to that index. + +Values stored in ``BPF_MAP_TYPE_ARRAY`` can be accessed by multiple programs across different CPUs. +To restrict storage to a single CPU, you may use a ``BPF_MAP_TYPE_PERCPU_ARRAY``. +Since Kernel version 5.1, the BPF infrastructure provides ``struct bpf_spin_lock`` to synchronize access. + +``bpf_map_get_next_key()`` can be used to iterate over array values. + +Examples +======== + +Please see the `tools/testing/selftests/bpf`_ directory for functional examples. +This sample code simply demonstrates the API. + +.. section links +.. _tools/testing/selftests/bpf: + https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/testing/selftests/bpf + +Kernel +------ + +.. code-block:: c + + struct { + __uint(type, BPF_MAP_TYPE_ARRAY); + __type(key, u32); + __type(value, long); + __uint(max_entries, 256); + } my_map SEC(".maps"); + + int bpf_prog(struct __sk_buff *skb) + { + int index = load_byte(skb, ETH_HLEN + offsetof(struct iphdr, protocol)); + long *value; + + if (skb->pkt_type != PACKET_OUTGOING) + return 0; + + value = bpf_map_lookup_elem(&my_map, &index); + if (value) + __sync_fetch_and_add(value, skb->len); + + return 0; + } + +Userspace +--------- + +BPF_MAP_TYPE_ARRAY +~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + #include <assert.h> + #include <bpf/libbpf.h> + #include <bpf/bpf.h> + + int main(int argc, char **argv) + { + int fd; + int ret = 0; + __u32 i, j; + __u32 index = 42; + long v, value; + + fd = bpf_create_map(BPF_MAP_TYPE_ARRAY, sizeof(__u32), sizeof(long), 256, 0); + if (fd < 0) + return fd; + + /* fill the map with values from 0-255 */ + for (i = 0; i < 256 ; i++) { + ret = bpf_map_update_elem(fd, &i, &v, BPF_ANY); + if (ret < 0) + return ret; + } + + ret = bpf_map_lookup_elem(fd, &index, &value); + if (ret < 0) + return ret; + + assert(value == 42); + + return ret; + } + + +BPF_MAP_TYPE_PERCPU_ARRAY +~~~~~~~~~~~~~~~~~~~~~~~~~ + +.. code-block:: c + + #include <assert.h> + #include <bpf/libbpf.h> + #include <bpf/bpf.h> + + int main(int argc, char **argv) + { + int ncpus = libbpf_num_possible_cpus(); + if (ncpus < 0) + return ncpus; + + int fd; + int ret = 0; + __u32 i, j; + __u32 index = 42; + long v[ncpus], value[ncpus]; + + + fd = bpf_create_map(BPF_MAP_TYPE_PERCPU_ARRAY, sizeof(__u32), sizeof(long), 256, 0); + if (fd < 0) + return -1; + + /* fill the map with values from 0-255 for each cpu */ + for (i = 0; i < 256 ; i++) { + for (j = 0; j < ncpus; j++) + v[j] = i; + ret = bpf_map_update_elem(fd, &i, &v, BPF_ANY); + if (ret < 0) + return ret; + } + + ret = bpf_map_lookup_elem(fd, &index, &value); + if (ret < 0) + return ret; + + for (j = 0; j < ncpus; j++) + assert(value[j] == 42); + + return ret; + } + +Semantics +========= + +As illustrated in the example above, when using a ``BPF_MAP_TYPE_PERCPU_ARRAY`` in userspace, the +values are an array with ``ncpus`` elements. + +When calling ``bpf_map_update_elem()`` the flags ``BPF_NOEXIST`` can not be used for these maps. \ No newline at end of file -- 2.33.1 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-11-23 16:24 ` [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker @ 2021-11-27 2:05 ` Song Liu 2021-12-02 20:08 ` Andrii Nakryiko 1 sibling, 0 replies; 6+ messages in thread From: Song Liu @ 2021-11-27 2:05 UTC (permalink / raw) To: Dave Tucker Cc: bpf, Jonathan Corbet, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Martin KaFai Lau, Song Liu, John Fastabend, KP Singh, Linux Doc Mailing List On Tue, Nov 23, 2021 at 8:24 AM Dave Tucker <dave@dtucker.co.uk> wrote: > > This commit adds documentation for the BPF_MAP_TYPE_ARRAY including > kernel version introduced, usage and examples. > It also documents BPF_MAP_TYPE_PERCPU_ARRAY since this is similar. > > Signed-off-by: Dave Tucker <dave@dtucker.co.uk> It will be great to add an example with BPF_F_MMAPABLE, but I guess we can do that in a follow up patch. So Acked-by: Song Liu <songliubraving@fb.com> With one nitpick. [...] > + > +When calling ``bpf_map_update_elem()`` the flags ``BPF_NOEXIST`` can not be used for these maps. > \ No newline at end of file nit: Maybe add a newline at the end? > -- > 2.33.1 > ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-11-23 16:24 ` [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-11-27 2:05 ` Song Liu @ 2021-12-02 20:08 ` Andrii Nakryiko 1 sibling, 0 replies; 6+ messages in thread From: Andrii Nakryiko @ 2021-12-02 20:08 UTC (permalink / raw) To: Dave Tucker Cc: bpf, Jonathan Corbet, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Martin Lau, Song Liu, john fastabend, KP Singh, Linux Doc Mailing List On Tue, Nov 23, 2021 at 8:24 AM Dave Tucker <dave@dtucker.co.uk> wrote: > > This commit adds documentation for the BPF_MAP_TYPE_ARRAY including > kernel version introduced, usage and examples. > It also documents BPF_MAP_TYPE_PERCPU_ARRAY since this is similar. > > Signed-off-by: Dave Tucker <dave@dtucker.co.uk> > --- It looks good, thanks for the update. But it seems like all the Documentation/bpf/*.rst are 80-char wrapped, can you please wrap the lines to fit within 80 characters for consistency? It also helps immensely when reading source text files and not the HTML-rendered version. > Documentation/bpf/map_array.rst | 172 ++++++++++++++++++++++++++++++++ > 1 file changed, 172 insertions(+) > create mode 100644 Documentation/bpf/map_array.rst > [...] ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage 2021-11-23 16:24 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker 2021-11-23 16:24 ` [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker @ 2021-11-27 1:53 ` Song Liu 1 sibling, 0 replies; 6+ messages in thread From: Song Liu @ 2021-11-27 1:53 UTC (permalink / raw) To: Dave Tucker Cc: bpf, Jonathan Corbet, Alexei Starovoitov, Daniel Borkmann, Andrii Nakryiko, Martin KaFai Lau, Song Liu, John Fastabend, KP Singh, Linux Doc Mailing List On Tue, Nov 23, 2021 at 8:24 AM Dave Tucker <dave@dtucker.co.uk> wrote: > > This adds the version at which this map became available to use in the > documentation > > Signed-off-by: Dave Tucker <dave@dtucker.co.uk> Acked-by: Song Liu <songliubraving@fb.com> ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-12-02 20:09 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-11-23 16:24 [PATCH v2 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-11-23 16:24 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker 2021-11-23 16:24 ` [PATCH v2 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-11-27 2:05 ` Song Liu 2021-12-02 20:08 ` Andrii Nakryiko 2021-11-27 1:53 ` [PATCH v2 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Song Liu
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