Re: [PATCH v3 5/6] tools/libxl: Extend datacopier to support reading into a buffer

From: Ian Campbell <Ian.Campbell@citrix.com>
To: Ian Jackson <Ian.Jackson@eu.citrix.com>
Cc: Ross Lagerwall <ross.lagerwall@citrix.com>,
	Andrew Cooper <andrew.cooper3@citrix.com>,
	Wei Liu <wei.liu2@citrix.com>,
	xen-devel@lists.xen.org
Subject: Re: [PATCH v3 5/6] tools/libxl: Extend datacopier to support reading into a buffer
Date: Wed, 1 Apr 2015 16:59:52 +0100	[thread overview]
Message-ID: <1427903992.13425.25.camel@citrix.com> (raw)
In-Reply-To: <21788.5271.661820.56568@mariner.uk.xensource.com>

On Wed, 2015-04-01 at 16:53 +0100, Ian Jackson wrote:
> >  /* onwrite==1 means failure happened when writing, logged, errnoval is valid
> >   * onwrite==0 means failure happened when reading
> > - *     errnoval==0 means we got eof and all data was written
> > - *     errnoval!=0 means we had a read error, logged
> > + *     errnoval>=0 means we got eof and all data was written or number of bytes
> > + *                 written when in read mode
> > + *     errnoval<0 means we had a read error, logged
> 
> I don't like this API.  Are you encoding a size in errnoval ?

Note that this aspect has since been reverted since it also broke
things. Ross was going to look for another way to achieve it, and this:

> Perhaps it would be better to include "bytes read" and "bytes written"
> fields in the dc state structure.

Sounds like a very plausible answer.

Ian.