Re: [PATCH] genl: Add l_genl_msg_attr_append_data

[Denis Kenzior <denkenz@gmail.com>]

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Hi Andrew,

On 10/05/2016 05:45 PM, Andrew Zaborowski wrote:
> Try to minimise the amount of buffers allocated and copied by clients
> when building a message attribute that is a concatenation of other
> buffers, such as an IE sequence.  The client would the following three
> calls:
>
> l_genl_msg_enter_nested
> l_genl_msg_attr_append_data
> l_genl_msg_leave_nested

So the intent here is that instead of:
msg = l_genl_msg_new_sized(...);
buf = alloca();
// memcpy / scribble in buffer
l_genl_msg_append_attr(msg, NL80211_ATTR_IE, buf_len, buf);

we do something like:
msg = l_genl_msg_new_sized(...);
l_genl_msg_enter_nested(msg, NL80211_ATTR_IE);
buf = l_genl_msg_attr_append_data(msg, len);
// scribble in buf
buf = l_genl_msg_attr_append_data(msg, len);
// scribble in buf
l_genl_msg_leave_nested(msg);

?

If so, you're (very creatively) really abusing the intent of 
enter_nested which is used for true nested attributes.  Don't think I 
really like that...

Is l_genl_msg_append_attrv(msg, iov, iov_len) not sufficient?

Alternatively, we should do something like:

l_genl_msg_attr_open(msg, NL80211_ATTR_IE);
l_genl_msg_attr_reserve(msg, len);
l_genl_msg_attr_append(msg, len, data);
l_genl_msg_attr_reserve(msg, len);
l_genl_msg_attr_close(msg);

Regards,
-Denis