linux-kernel - Re: Draft 3 of bpf(2) man page for review

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Date:	Thu, 23 Jul 2015 11:58:01 +0200
From:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	Daniel Borkmann <daniel@...earbox.net>
CC:	mtk.manpages@...il.com, linux-man <linux-man@...r.kernel.org>,
	linux-kernel@...r.kernel.org, Silvan Jegen <s.jegen@...il.com>,
	Walter Harms <wharms@....de>
Subject: Re: Draft 3 of bpf(2) man page for review

On 07/23/2015 12:12 AM, Alexei Starovoitov wrote:
> On 7/22/15 1:10 PM, Michael Kerrisk (man-pages) wrote:
>>         BPF  maps  are  a generic data structure for storage of different
>>         data types.  A  user  process  can  create  multiple  maps  (with
>>         key/value-pairs  being  opaque bytes of data) and access them via
>>         file descriptors.  Differnt eBPF programs  can  access  the  same
>>         maps  in  parallel.  It's up to the user process and eBPF program
>>         to decide what they store inside maps.
> 
> typo in 'Different'

Fixed.

>>     eBPF program types
>>         By picking prog_type, the program author selects a set of  helper
>>         functions that can be called from the eBPF program and the corre‐
>>         sponding format of struct bpf_context (which  is  the  data  blob
>>         passed  into  the eBPF program as the first argument).  For exam‐
>>         ple,     programs     loaded     with     a     prog_type      of
>>         BPF_PROG_TYPE_SOCKET_FILTER  may  call  the bpf_map_lookup_elem()
>>         helper, whereas some other program  types  may  not  be  able  to
>>         employ  this helper.  The set of functions available to eBPF pro‐
>>         grams of a given type may increase in the future.
> 
> overall it's all correct, but today bpf_map_lookup_elem() is allowed
> for all program types. May be change that to:
> "BPF_PROG_TYPE_KPROBE may call the bpf_probe_read() helper"
> since only type_kprobe programs can call it.
> type_sockets/type_sched_* cannot.

Changed, as you suggest.

>>                The bpf_context argument is a pointer to a struct sk_buff.
>>                Programs cannot access the fields of sk_buff directly.
> 
> Probably drop last sentence and replace 'sk_buff' with '__sk_buff'
> in the first? Or for the first version we can drop both sentences.

I did the former.

> The rest looks great. Thank you much!

Thanks,

Michael



-- 
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
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