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2f968e9f4a
Add non-mmapable data section to test_skeleton selftest and make sure it
really isn't mmapable by trying to mmap() it anyways.
Also make sure that libbpf doesn't report BPF_F_MMAPABLE flag to users.
Additional, some more manual testing was performed that this feature
works as intended.
Looking at created map through bpftool shows that flags passed to kernel are
indeed zero:
$ bpftool map show
...
1782: array name .data.non_mmapa flags 0x0
key 4B value 16B max_entries 1 memlock 4096B
btf_id 1169
pids test_progs(8311)
...
Checking BTF uploaded to kernel for this map shows that zero_key and
zero_value are indeed marked as static, even though zero_key is actually
original global (but STV_HIDDEN) variable:
$ bpftool btf dump id 1169
...
[51] VAR 'zero_key' type_id=2, linkage=static
[52] VAR 'zero_value' type_id=7, linkage=static
...
[62] DATASEC '.data.non_mmapable' size=16 vlen=2
type_id=51 offset=0 size=4 (VAR 'zero_key')
type_id=52 offset=4 size=12 (VAR 'zero_value')
...
And original BTF does have zero_key marked as linkage=global:
$ bpftool btf dump file test_skeleton.bpf.linked3.o
...
[51] VAR 'zero_key' type_id=2, linkage=global
[52] VAR 'zero_value' type_id=7, linkage=static
...
[62] DATASEC '.data.non_mmapable' size=16 vlen=2
type_id=51 offset=0 size=4 (VAR 'zero_key')
type_id=52 offset=4 size=12 (VAR 'zero_value')
Bpftool didn't require any changes at all because it checks whether internal
map is mmapable already, but just to double-check generated skeleton, we
see that .data.non_mmapable neither sets mmaped pointer nor has
a corresponding field in the skeleton:
$ grep non_mmapable test_skeleton.skel.h
struct bpf_map *data_non_mmapable;
s->maps[7].name = ".data.non_mmapable";
s->maps[7].map = &obj->maps.data_non_mmapable;
But .data.read_mostly has all of those things:
$ grep read_mostly test_skeleton.skel.h
struct bpf_map *data_read_mostly;
struct test_skeleton__data_read_mostly {
int read_mostly_var;
} *data_read_mostly;
s->maps[6].name = ".data.read_mostly";
s->maps[6].map = &obj->maps.data_read_mostly;
s->maps[6].mmaped = (void **)&obj->data_read_mostly;
_Static_assert(sizeof(s->data_read_mostly->read_mostly_var) == 4, "unexpected size of 'read_mostly_var'");
Acked-by: Stanislav Fomichev <sdf@google.com>
Acked-by: Dave Marchevsky <davemarchevsky@fb.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/r/20221019002816.359650-4-andrii@kernel.org
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.