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libbpf: Remove mode check in libbpf_set_strict_mode()

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libbpf_set_strict_mode() checks that the passed mode doesn't contain
extra bits for LIBBPF_STRICT_* flags that don't exist yet.

It makes it difficult for applications to disable some strict flags as
something like "LIBBPF_STRICT_ALL & ~LIBBPF_STRICT_MAP_DEFINITIONS"
is rejected by this check and they have to use a rather complicated
formula to calculate it.[0]

One possibility is to change LIBBPF_STRICT_ALL to only contain the bits
of all existing LIBBPF_STRICT_* flags instead of 0xffffffff. However
it's not possible because the idea is that applications compiled against
older libbpf_legacy.h would still be opting into latest
LIBBPF_STRICT_ALL features.[1]

The other possibility is to remove that check so something like
"LIBBPF_STRICT_ALL & ~LIBBPF_STRICT_MAP_DEFINITIONS" is allowed. It's
what this commit does.

[0]: https://lore.kernel.org/bpf/20220204220435.301896-1-mauricio@kinvolk.io/
[1]: https://lore.kernel.org/bpf/CAEf4BzaTWa9fELJLh+bxnOb0P1EMQmaRbJVG0L+nXZdy0b8G3Q@mail.gmail.com/

Fixes: 93b8952d223a ("libbpf: deprecate legacy BPF map definitions")
Signed-off-by: Mauricio Vásquez <mauricio@kinvolk.io>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220207145052.124421-2-mauricio@kinvolk.io
This commit is contained in:
Mauricio Vásquez 2022-02-07 09:50:50 -05:00 committed by Andrii Nakryiko
parent e91d280c84
commit e4e835c87b
1 changed files with 0 additions and 8 deletions
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8
tools/lib/bpf/libbpf.c
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@ -156,14 +156,6 @@ enum libbpf_strict_mode libbpf_mode = LIBBPF_STRICT_NONE;
int libbpf_set_strict_mode(enum libbpf_strict_mode mode)
{
/* __LIBBPF_STRICT_LAST is the last power-of-2 value used + 1, so to
* get all possible values we compensate last +1, and then (2*x - 1)
* to get the bit mask
*/
if (mode != LIBBPF_STRICT_ALL
&& (mode & ~((__LIBBPF_STRICT_LAST - 1) * 2 - 1)))
return errno = EINVAL, -EINVAL;
libbpf_mode = mode;
return 0;
}