linux-kernel - RE: [Patch v2 11/15] CIFS: Pass page offset for calculating signature

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Message-ID: <DM5PR2101MB0728DDBD53A756B6CEB9EEAECE490@DM5PR2101MB0728.namprd21.prod.outlook.com>
Date:   Tue, 26 Jun 2018 04:15:15 +0000
From:   Long Li <longli@...rosoft.com>
To:     Tom Talpey <tom@...pey.com>, Steve French <sfrench@...ba.org>,
        "linux-cifs@...r.kernel.org" <linux-cifs@...r.kernel.org>,
        "samba-technical@...ts.samba.org" <samba-technical@...ts.samba.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>
Subject: RE: [Patch v2 11/15] CIFS: Pass page offset for calculating signature

> Subject: Re: [Patch v2 11/15] CIFS: Pass page offset for calculating signature
> 
> On 5/30/2018 3:48 PM, Long Li wrote:
> > From: Long Li <longli@...rosoft.com>
> >
> > When calculating signature for the packet, it needs to read into the
> > correct page offset for the data.
> >
> > Signed-off-by: Long Li <longli@...rosoft.com>
> > ---
> >   fs/cifs/cifsencrypt.c | 9 +++++----
> >   1 file changed, 5 insertions(+), 4 deletions(-)
> >
> > diff --git a/fs/cifs/cifsencrypt.c b/fs/cifs/cifsencrypt.c index
> > a6ef088..e88303c 100644
> > --- a/fs/cifs/cifsencrypt.c
> > +++ b/fs/cifs/cifsencrypt.c
> > @@ -68,11 +68,12 @@ int __cifs_calc_signature(struct smb_rqst *rqst,
> >
> >   	/* now hash over the rq_pages array */
> >   	for (i = 0; i < rqst->rq_npages; i++) {
> > -		void *kaddr = kmap(rqst->rq_pages[i]);
> > -		size_t len = rqst->rq_pagesz;
> > +		void *kaddr;
> > +		unsigned int len, offset;
> >
> > -		if (i == rqst->rq_npages - 1)
> > -			len = rqst->rq_tailsz;
> > +		rqst_page_get_length(rqst, i, &len, &offset);
> > +
> > +		kaddr = (char *) kmap(rqst->rq_pages[i]) + offset;
> 
> I suppose it's more robust to map a page at a time, but it's pretty expensive.
> Is this the only way to iterate over a potentially very large block of data? For
> example, a 1MB segment means 256 kmap/kunmaps.

I will look into not mapping those pages while doing I/O.

This code path is for RDMA send/receive, and it's rarely used for transferring large amount of data.

> 
> Tom.
> 
> >
> >   		crypto_shash_update(shash, kaddr, len);
> >
> >