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SubjectRe: [PATCH bpf-next] libbpf: handle ENOTSUPP errno in libbpf_strerror()
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On 4/25/21 12:16 AM, Pedro Tammela wrote:
> The 'bpf()' syscall is leaking the ENOTSUPP errno that is internal to the kernel[1].
> More recent code is already using the correct EOPNOTSUPP, but changing
> older return codes is not possible due to dependency concerns, so handle ENOTSUPP
> in libbpf_strerror().
>
> [1] https://lore.kernel.org/netdev/20200511165319.2251678-1-kuba@kernel.org/
>
> Signed-off-by: Pedro Tammela <pctammela@mojatatu.com>
> ---
> tools/lib/bpf/libbpf_errno.c | 9 +++++++++
> 1 file changed, 9 insertions(+)
>
> diff --git a/tools/lib/bpf/libbpf_errno.c b/tools/lib/bpf/libbpf_errno.c
> index 0afb51f7a919..7de8bbc34a37 100644
> --- a/tools/lib/bpf/libbpf_errno.c
> +++ b/tools/lib/bpf/libbpf_errno.c
> @@ -13,6 +13,9 @@
>
> #include "libbpf.h"
>
> +/* This errno is internal to the kernel but leaks in the bpf() syscall. */
> +#define ENOTSUPP 524
> +
> /* make sure libbpf doesn't use kernel-only integer typedefs */
> #pragma GCC poison u8 u16 u32 u64 s8 s16 s32 s64
>
> @@ -43,6 +46,12 @@ int libbpf_strerror(int err, char *buf, size_t size)
>
> err = err > 0 ? err : -err;
>
> + if (err == ENOTSUPP) {
> + snprintf(buf, size, "Operation not supported");
> + buf[size - 1] = '\0';
> + return 0;
> + }
> +
> if (err < __LIBBPF_ERRNO__START) {
> int ret;

Could you fold this into the __LIBBPF_ERRNO__START test body to denote that it
belongs outside the libbpf error range? For example, could be simplified like this:

if (err < __LIBBPF_ERRNO__START) {
int ret;

/* Handle ENOTSUPP separate here given it's kernel internal,
* but for sake of error string it has the same meaning as
* the EOPNOTSUPP error.
*/
if (err == ENOTSUPP)
err = EOPNOTSUPP;
ret = strerror_r(err, buf, size);
buf[size - 1] = '\0';
return ret;
}

Thanks,
Daniel

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