Re: [RFC PATCH 04/35] ceph: Convert ceph_mds_request::r_pagelist to a databuf

[David Howells]

Viacheslav Dubeyko <Slava.Dubeyko@xxxxxxx> wrote:

> > > > +	if (ceph_databuf_insert_frag(dbuf, 0, sizeof(*header),
> > > > GFP_KERNEL) < 0)
> > > > +		goto out;
> > > > +	if (ceph_databuf_insert_frag(dbuf, 1, PAGE_SIZE, GFP_KERNEL)
> > > > < 0)
> > > >  		goto out;
> > > >  
> > > > +	iov_iter_bvec(&iter, ITER_DEST, &dbuf->bvec[1], 1, len);
> > > 
> > > Is it correct &dbuf->bvec[1]? Why do we work with item #1? I think it
> > > looks confusing.
> > 
> > Because you have a protocol element (in dbuf->bvec[0]) and a buffer (in
> > dbuf->bvec[1]).
> 
> It sounds to me that we need to have two declarations (something like this):
> 
> #define PROTOCOL_ELEMENT_INDEX    0
> #define BUFFER_INDEX              1

But that's specific to this particular usage.  There may or may not be a
frag/page allocated to a protocol element and there may or may not be buffer
parts and may be multiple buffer parts.  There could even be multiple pages
allocated to protocol elements.

David