* [PATCH v3 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY @ 2021-12-07 13:31 Dave Tucker 2021-12-07 13:31 ` [PATCH v3 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker 2021-12-07 13:31 ` [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker 0 siblings, 2 replies; 6+ messages in thread From: Dave Tucker @ 2021-12-07 13:31 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 v2->v3: - wrap text to 80 chars and add newline at end of file 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 | 182 +++++++++++++++++++++++ Documentation/bpf/map_cgroup_storage.rst | 2 + 2 files changed, 184 insertions(+) create mode 100644 Documentation/bpf/map_array.rst -- 2.33.1 ^ permalink raw reply [flat|nested] 6+ messages in thread
* [PATCH v3 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage 2021-12-07 13:31 [PATCH v3 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY Dave Tucker @ 2021-12-07 13:31 ` Dave Tucker 2021-12-07 13:31 ` [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker 1 sibling, 0 replies; 6+ messages in thread From: Dave Tucker @ 2021-12-07 13:31 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 v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-12-07 13:31 [PATCH v3 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-12-07 13:31 ` [PATCH v3 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker @ 2021-12-07 13:31 ` Dave Tucker 2021-12-07 14:53 ` Jonathan Corbet 1 sibling, 1 reply; 6+ messages in thread From: Dave Tucker @ 2021-12-07 13:31 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 | 182 ++++++++++++++++++++++++++++++++ 1 file changed, 182 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..7ed5f7654ee8 --- /dev/null +++ b/Documentation/bpf/map_array.rst @@ -0,0 +1,182 @@ +.. 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. + -- 2.33.1 ^ permalink raw reply related [flat|nested] 6+ messages in thread
* Re: [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-12-07 13:31 ` [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker @ 2021-12-07 14:53 ` Jonathan Corbet 2021-12-07 15:29 ` Dave Tucker 0 siblings, 1 reply; 6+ messages in thread From: Jonathan Corbet @ 2021-12-07 14:53 UTC (permalink / raw) To: Dave Tucker, bpf Cc: ast, daniel, andrii, kafai, songliubraving, john.fastabend, kpsingh, linux-doc, Dave Tucker Dave Tucker <dave@dtucker.co.uk> writes: > 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 | 182 ++++++++++++++++++++++++++++++++ > 1 file changed, 182 insertions(+) > create mode 100644 Documentation/bpf/map_array.rst When you add a new file, you need to add it to index.rst as well to bring it into the docs build. > diff --git a/Documentation/bpf/map_array.rst b/Documentation/bpf/map_array.rst > new file mode 100644 > index 000000000000..7ed5f7654ee8 > --- /dev/null > +++ b/Documentation/bpf/map_array.rst > @@ -0,0 +1,182 @@ > +.. 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. It's really better not to use ``literal markup`` for function names. Just write function() and the right thing will happen, including cross-reference links to the kerneldoc for that function if it exists. Thanks, jon ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-12-07 14:53 ` Jonathan Corbet @ 2021-12-07 15:29 ` Dave Tucker 2021-12-07 15:36 ` Jonathan Corbet 0 siblings, 1 reply; 6+ messages in thread From: Dave Tucker @ 2021-12-07 15:29 UTC (permalink / raw) To: Jonathan Corbet, bpf Cc: ast, daniel, andrii, kafai, songliubraving, john.fastabend, kpsingh, linux-doc On Tue, 7 Dec 2021, at 14:53, Jonathan Corbet wrote: > Dave Tucker <dave@dtucker.co.uk> writes: > >> 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 | 182 ++++++++++++++++++++++++++++++++ >> 1 file changed, 182 insertions(+) >> create mode 100644 Documentation/bpf/map_array.rst > > When you add a new file, you need to add it to index.rst as well to > bring it into the docs build. I believe I responded to this comment in an earlier version of this patch set. The glob pattern in Documentaion/bpf/maps.rst includes this in the docs build. >> diff --git a/Documentation/bpf/map_array.rst b/Documentation/bpf/map_array.rst >> new file mode 100644 >> index 000000000000..7ed5f7654ee8 >> --- /dev/null >> +++ b/Documentation/bpf/map_array.rst >> @@ -0,0 +1,182 @@ >> +.. 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. > > It's really better not to use ``literal markup`` for function names. > Just write function() and the right thing will happen, including > cross-reference links to the kerneldoc for that function if it exists. I've just tested this out, and for some reason it's not working as expected. It's not formatted as ``literal markup`` nor is it linked to kerneldoc. Perhaps because the issue is because these are part of tools/lib/bpf/bpf_helpers.h? I also noticed I introduced a warning due to missing a newline after a code block :( I'll fix that and push a v4, but will wait for confirmation on the use of `` for the helper functions. - Dave > Thanks, > > jon ^ permalink raw reply [flat|nested] 6+ messages in thread
* Re: [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY 2021-12-07 15:29 ` Dave Tucker @ 2021-12-07 15:36 ` Jonathan Corbet 0 siblings, 0 replies; 6+ messages in thread From: Jonathan Corbet @ 2021-12-07 15:36 UTC (permalink / raw) To: Dave Tucker, bpf Cc: ast, daniel, andrii, kafai, songliubraving, john.fastabend, kpsingh, linux-doc "Dave Tucker" <dave@dtucker.co.uk> writes: > On Tue, 7 Dec 2021, at 14:53, Jonathan Corbet wrote: >> Dave Tucker <dave@dtucker.co.uk> writes: >> >>> 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 | 182 ++++++++++++++++++++++++++++++++ >>> 1 file changed, 182 insertions(+) >>> create mode 100644 Documentation/bpf/map_array.rst >> >> When you add a new file, you need to add it to index.rst as well to >> bring it into the docs build. > > I believe I responded to this comment in an earlier version of this patch set. > The glob pattern in Documentaion/bpf/maps.rst includes this in the docs build. Sorry...I even looked for :glob:, believe it or not, but not in linux-next, sorry. Caffeine is taking effect now... >> It's really better not to use ``literal markup`` for function names. >> Just write function() and the right thing will happen, including >> cross-reference links to the kerneldoc for that function if it exists. > > I've just tested this out, and for some reason it's not working as expected. > It's not formatted as ``literal markup`` nor is it linked to kerneldoc. > Perhaps because the issue is because these are part of tools/lib/bpf/bpf_helpers.h? It can only link to kerneldoc that's actually pulled into the built documentation. If there isn't a ".. kernel-doc::" directive for that file (and it appears there is not) then Sphinx doesn't know about it. Thanks, jon ^ permalink raw reply [flat|nested] 6+ messages in thread
end of thread, other threads:[~2021-12-07 15:36 UTC | newest] Thread overview: 6+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- 2021-12-07 13:31 [PATCH v3 bpf-next 0/2] bpf, docs: Document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-12-07 13:31 ` [PATCH v3 bpf-next 1/2] bpf, docs: add kernel version to map_cgroup_storage Dave Tucker 2021-12-07 13:31 ` [PATCH v3 bpf-next 2/2] bpf, docs: document BPF_MAP_TYPE_ARRAY Dave Tucker 2021-12-07 14:53 ` Jonathan Corbet 2021-12-07 15:29 ` Dave Tucker 2021-12-07 15:36 ` Jonathan Corbet
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