linux-kernel - RE: [Patch v2 06/15] CIFS: Introduce helper function to get page offset and length in smb

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Message-ID: <CY4PR2101MB0722840106EDFEFBBA42D45FCE4A0@CY4PR2101MB0722.namprd21.prod.outlook.com>
Date:   Mon, 25 Jun 2018 21:14:31 +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 06/15] CIFS: Introduce helper function to get page
 offset and length in smb_rqst

> Subject: Re: [Patch v2 06/15] CIFS: Introduce helper function to get page
> offset and length in smb_rqst
> 
> On 5/30/2018 3:47 PM, Long Li wrote:
> > From: Long Li <longli@...rosoft.com>
> >
> > Introduce a function rqst_page_get_length to return the page offset
> > and length for a given page in smb_rqst. This function is to be used
> > by following patches.
> >
> > Signed-off-by: Long Li <longli@...rosoft.com>
> > ---
> >   fs/cifs/cifsproto.h |  3 +++
> >   fs/cifs/misc.c      | 17 +++++++++++++++++
> >   2 files changed, 20 insertions(+)
> >
> > diff --git a/fs/cifs/cifsproto.h b/fs/cifs/cifsproto.h index
> > 7933c5f..89dda14 100644
> > --- a/fs/cifs/cifsproto.h
> > +++ b/fs/cifs/cifsproto.h
> > @@ -557,4 +557,7 @@ int cifs_alloc_hash(const char *name, struct
> crypto_shash **shash,
> >   		    struct sdesc **sdesc);
> >   void cifs_free_hash(struct crypto_shash **shash, struct sdesc
> > **sdesc);
> >
> > +extern void rqst_page_get_length(struct smb_rqst *rqst, unsigned int
> page,
> > +				unsigned int *len, unsigned int *offset);
> > +
> >   #endif			/* _CIFSPROTO_H */
> > diff --git a/fs/cifs/misc.c b/fs/cifs/misc.c index 96849b5..e951417
> > 100644
> > --- a/fs/cifs/misc.c
> > +++ b/fs/cifs/misc.c
> > @@ -905,3 +905,20 @@ cifs_free_hash(struct crypto_shash **shash,
> struct sdesc **sdesc)
> >   		crypto_free_shash(*shash);
> >   	*shash = NULL;
> >   }
> > +
> > +/**
> > + * rqst_page_get_length - obtain the length and offset for a page in
> > +smb_rqst
> > + * Input: rqst - a smb_rqst, page - a page index for rqst
> > + * Output: *len - the length for this page, *offset - the offset for
> > +this page  */ void rqst_page_get_length(struct smb_rqst *rqst,
> > +unsigned int page,
> > +				unsigned int *len, unsigned int *offset) {
> > +	*len = rqst->rq_pagesz;
> > +	*offset = (page == 0) ? rqst->rq_offset : 0;
> 
> Really? Page 0 always has a zero offset??

I think you are misreading this line. The offset for page 0 is rq_offset, the offset for all subsequent pages are 0.

> 
> > +
> > +	if (rqst->rq_npages == 1 || page == rqst->rq_npages-1)
> > +		*len = rqst->rq_tailsz;
> > +	else if (page == 0)
> > +		*len = rqst->rq_pagesz - rqst->rq_offset; }
> >
> 
> This subroutine does what patch 5 does inline. Why not push this patch up in
> the sequence and use the helper?

This is actually a little different. This function returns the length and offset for a given page in the request. There might be multiple pages in a request. 

The other function calculates the total length of all the pages in a request.

> 
> Tom.