Subject: Re: [PATCHSET v6 0/26] pnfs for 2.6.40
From: Trond Myklebust <Trond.Myklebust@netapp.com>
To: Boaz Harrosh <bharrosh@panasas.com>
Cc: bhalevy@panasas.com, linux-nfs@vger.kernel.org
Date: Tue, 24 May 2011 12:21:46 -0400
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On Tue, 2011-05-24 at 18:56 +0300, Boaz Harrosh wrote: 
> In the nfs_pageio_descriptor passed to pg_test() together with the two pages:
> Which member means the current byte_size (or page_count?) and what is the
> meaning of some of these fields
> 
> struct nfs_pageio_descriptor {
>         ....
> 	unsigned long		pg_bytes_written;
> 		Is this for result after read/write?

This is the total number of bytes we successfully called
nfs_pageio_doio() for. In other words, it should represent the total
number of bytes we put on the wire.

> 	size_t			pg_count;
> 		Is this the number of pages added up to now?
> 		Do we also have the start of the first page?

This is the number of bytes we have successfully coalesced into the
current i/o.

> 	size_t			pg_bsize;
> 		So I understand this is the max allowed pages. Does
> 		that mean also the allocated size or Just the negotiated
> 		size with the server? (Really bad name if you ask me)

It means the 'block size'. In ordinary NFS parlance that will be the
'rsize' or the 'wsize'.

> 	unsigned int		pg_base;
> 		Is that the index of the first page? That cannot be, the page->index
> 		needs to be 64bit. So what is this then?

It is used when dealing with I/O requests that are not page aligned.

If you consider the pages that we are to write out in the current I/O as
a single buffer, then the pg_base is the offset of the first byte to
write out/read in.

-- 
Trond Myklebust
Linux NFS client maintainer

NetApp
Trond.Myklebust@netapp.com
www.netapp.com