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SubjectRE: [Patch v2 11/15] CIFS: Pass page offset for calculating signature
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> 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@microsoft.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@microsoft.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);
> >
> >
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