Re: [Patch v2 06/15] CIFS: Introduce helper function to get page offset and length in smb_rqst

[Tom Talpey]

On 6/25/2018 5:14 PM, Long Li wrote:
> > 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@xxxxxxxxxxxxx>
> > >
> > > 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@xxxxxxxxxxxxx>
> > > ---
> > >    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.

Ah, yes, sorry I did read it incorrectly.
> > > +
> > > +	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.

Ok, but I still think there is quite a bit of inline computation of
this stuff that would more clearly and more robustly be done in a set
of common functions. If someone ever touches the code to support a
new upper layer, or even integrate with more complex compounding,
things will get ugly fast.

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

Again, a great candidate for a common set of subroutines, IMO.

Tom.