linux-kernel - Re: [Patch v2 02/15] CIFS: Add support for direct pages in rdata

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Message-ID: <20180625210132.GB5381@ziepe.ca>
Date:   Mon, 25 Jun 2018 15:01:32 -0600
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Tom Talpey <tom@...pey.com>
Cc:     longli@...rosoft.com, Steve French <sfrench@...ba.org>,
        linux-cifs@...r.kernel.org, samba-technical@...ts.samba.org,
        linux-kernel@...r.kernel.org, linux-rdma@...r.kernel.org
Subject: Re: [Patch v2 02/15] CIFS: Add support for direct pages in rdata

On Sat, Jun 23, 2018 at 09:50:20PM -0400, Tom Talpey wrote:
> On 5/30/2018 3:47 PM, Long Li wrote:
> >From: Long Li <longli@...rosoft.com>
> >
> >Add a function to allocate rdata without allocating pages for data
> >transfer. This gives the caller an option to pass a number of pages
> >that point to the data buffer.
> >
> >rdata is still reponsible for free those pages after it's done.
> 
> "Caller" is still responsible? Or is the rdata somehow freeing itself
> via another mechanism?
> 
> >
> >Signed-off-by: Long Li <longli@...rosoft.com>
> >  fs/cifs/cifsglob.h |  2 +-
> >  fs/cifs/file.c     | 23 ++++++++++++++++++++---
> >  2 files changed, 21 insertions(+), 4 deletions(-)
> >
> >diff --git a/fs/cifs/cifsglob.h b/fs/cifs/cifsglob.h
> >index 8d16c3e..56864a87 100644
> >+++ b/fs/cifs/cifsglob.h
> >@@ -1179,7 +1179,7 @@ struct cifs_readdata {
> >  	unsigned int			tailsz;
> >  	unsigned int			credits;
> >  	unsigned int			nr_pages;
> >-	struct page			*pages[];
> >+	struct page			**pages;
> 
> Technically speaking, these are syntactically equivalent. It may not
> be worth changing this historic definition.

[] is a C99 'flex array', it has a different allocation behavior than
** and is not interchangeable..

Jason