[PATCH] bpf.2: Note that unused fields and padding in bpf_attr must be zero

[PATCH] bpf.2: Note that unused fields and padding in bpf_attr must be zero

[Jakub Sitnicki]

In a discussion regarding a potential backward incompatible change [1],
Andrii Nakryiko points out that unused bytes of bpf_attr should be
zero. Add this bit of information to the bpf(2) man page.

[1] https://lore.kernel.org/bpf/CAEf4BzbT4vQBnZzdD00SuPCDkeb4Cm=F6PLUoO_3X93UQD5hbQ@mail.gmail.com/

Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
---
 man2/bpf.2 | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/man2/bpf.2 b/man2/bpf.2
index 2d257eaa6..ee57226ee 100644
--- a/man2/bpf.2
+++ b/man2/bpf.2
@@ -142,7 +142,7 @@ provided via
 .IR attr ,
 which is a pointer to a union of type
 .I bpf_attr
-(see below).
+(see below). The unused fields and padding must be zeroed out before the call.
 The
 .I size
 argument is the size of the union pointed to by
-- 
2.35.1

Re: [PATCH] bpf.2: Note that unused fields and padding in bpf_attr must be zero

[Alejandro Colomar]

Hi Jakub,

On 4/25/22 18:08, Jakub Sitnicki wrote:
> In a discussion regarding a potential backward incompatible change [1],
> Andrii Nakryiko points out that unused bytes of bpf_attr should be
> zero. Add this bit of information to the bpf(2) man page.
> 
> [1] https://lore.kernel.org/bpf/CAEf4BzbT4vQBnZzdD00SuPCDkeb4Cm=F6PLUoO_3X93UQD5hbQ@mail.gmail.com/
> 
> Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>

Patch applied.

Thanks,

Alex

> ---
>   man2/bpf.2 | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/man2/bpf.2 b/man2/bpf.2
> index 2d257eaa6..ee57226ee 100644
> --- a/man2/bpf.2
> +++ b/man2/bpf.2
> @@ -142,7 +142,7 @@ provided via
>   .IR attr ,
>   which is a pointer to a union of type
>   .I bpf_attr
> -(see below).
> +(see below). The unused fields and padding must be zeroed out before the call.

But I changed it to add a separate line, instead of continuation in the 
same one.

>   The
>   .I size
>   argument is the size of the union pointed to by

Re: [PATCH] bpf.2: Note that unused fields and padding in bpf_attr must be zero

[Jakub Sitnicki]

On Mon, Apr 25, 2022 at 11:01 PM +02, Alejandro Colomar wrote:

[...]

>> diff --git a/man2/bpf.2 b/man2/bpf.2
>> index 2d257eaa6..ee57226ee 100644
>> --- a/man2/bpf.2
>> +++ b/man2/bpf.2
>> @@ -142,7 +142,7 @@ provided via
>>   .IR attr ,
>>   which is a pointer to a union of type
>>   .I bpf_attr
>> -(see below).
>> +(see below). The unused fields and padding must be zeroed out before the call.
>
> But I changed it to add a separate line, instead of continuation in the same
> one.
>

Thanks for the fixup, Alex. I will keep it in mind for the next time.