Proposal: Add M_HASCL().

[Andre Oppermann]

Bruce M. Simpson wrote:
> Bruce M Simpson wrote:
>> Much network code needs to know if the mbuf it is looking at is using 
>> a cluster. I propose putting M_HASCL() in sys/mbuf.h. I realise this 
>> is a style change, however, it seems to be a very common idiom.
> I sent this, then I looked at NetBSD, having caught a glimpse of their 
> MBUFTRACE code when skimming lots of diffs. That is also a good idea, 
> and might help us catch problems before they go prime-time; I've added 
> it to the wiki.
> 
> Point there is, M_HASCL() seems to be a hangover from the 4.4BSD era. 
> NetBSD seems to treat clusters and external storage as separate 
> entities. So I'm reconsidering this in the light of this new evidence.
> 
> As far as I understand it, the presence of M_EXT in an mbuf chain's 
> header in FreeBSD always indicate that we are using external storage 
> (not necessarily, but possibly, a cluster).
> 
> Can someone confirm this?

This is correct.  M_EXT is set whenever external storage is attached
to an mbuf.  We have many different classes of external storage with
traditional 2k clusters being one of them.

-- 
Andre