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SubjectRE: [Patch v2 05/15] CIFS: Calculate the correct request length based on page offset and tail size
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> Subject: Re: [Patch v2 05/15] CIFS: Calculate the correct request length based
> on page offset and tail size
>
> On 5/30/2018 3:47 PM, Long Li wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > It's possible that the page offset is non-zero in the pages in a
> > request, change the function to calculate the correct data buffer length.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> > fs/cifs/transport.c | 20 +++++++++++++++++---
> > 1 file changed, 17 insertions(+), 3 deletions(-)
> >
> > diff --git a/fs/cifs/transport.c b/fs/cifs/transport.c index
> > 927226a..d6b5523 100644
> > --- a/fs/cifs/transport.c
> > +++ b/fs/cifs/transport.c
> > @@ -212,10 +212,24 @@ rqst_len(struct smb_rqst *rqst)
> > for (i = 0; i < rqst->rq_nvec; i++)
> > buflen += iov[i].iov_len;
> >
> > - /* add in the page array if there is one */
> > + /*
> > + * Add in the page array if there is one. The caller needs to make
> > + * sure rq_offset and rq_tailsz are set correctly. If a buffer of
> > + * multiple pages ends at page boundary, rq_tailsz needs to be set to
> > + * PAGE_SIZE.
> > + */
> > if (rqst->rq_npages) {
> > - buflen += rqst->rq_pagesz * (rqst->rq_npages - 1);
> > - buflen += rqst->rq_tailsz;
> > + if (rqst->rq_npages == 1)
> > + buflen += rqst->rq_tailsz;
> > + else {
> > + /*
> > + * If there is more than one page, calculate the
> > + * buffer length based on rq_offset and rq_tailsz
> > + */
> > + buflen += rqst->rq_pagesz * (rqst->rq_npages - 1) -
> > + rqst->rq_offset;
> > + buflen += rqst->rq_tailsz;
> > + }
>
> Wouldn't it be simpler to keep the original code, but then just subtract the
> rq_offset?
>
> buflen += rqst->rq_pagesz * (rqst->rq_npages - 1);
> buflen += rqst->rq_tailsz;
> buflen -= rqst->rq_offset;
>
> It's kind of confusing as written. Also, what if it's just one page, but has a
> non-zero offset? Is that somehow not possible? My suggested code would
> take that into account, yours doesn't.

I think It can be changed to this:

buflen += rqst->rq_pagesz * (rqst->rq_npages - 1);
buflen += rqst->rq_tailsz;
if (rqst->rq_npages > 1)
buflen -= rqst->rq_offset;

This looks cleaner than before.

When there is only one page with a non-zero offset, rq_tailsz is the actual data length.

>
> Tom.
>
> > }
> >
> > return buflen;
> >
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