RE: [Patch v2 08/15] CIFS: SMBD: Support page offset in RDMA send

[Long Li <longli@microsoft.com>]

> Subject: Re: [Patch v2 08/15] CIFS: SMBD: Support page offset in RDMA send
> 
> On 5/30/2018 3:48 PM, Long Li wrote:
> > From: Long Li <longli@microsoft.com>
> >
> > The RDMA send function needs to look at offset in the request pages,
> > and send data starting from there.
> >
> > Signed-off-by: Long Li <longli@microsoft.com>
> > ---
> >   fs/cifs/smbdirect.c | 27 +++++++++++++++++++--------
> >   1 file changed, 19 insertions(+), 8 deletions(-)
> >
> > diff --git a/fs/cifs/smbdirect.c b/fs/cifs/smbdirect.c index
> > c62f7c9..6141e3c 100644
> > --- a/fs/cifs/smbdirect.c
> > +++ b/fs/cifs/smbdirect.c
> > @@ -17,6 +17,7 @@
> >   #include <linux/highmem.h>
> >   #include "smbdirect.h"
> >   #include "cifs_debug.h"
> > +#include "cifsproto.h"
> >
> >   static struct smbd_response *get_empty_queue_buffer(
> >   		struct smbd_connection *info);
> > @@ -2082,7 +2083,7 @@ int smbd_send(struct smbd_connection *info,
> struct smb_rqst *rqst)
> >   	struct kvec vec;
> >   	int nvecs;
> >   	int size;
> > -	int buflen = 0, remaining_data_length;
> > +	unsigned int buflen = 0, remaining_data_length;
> >   	int start, i, j;
> >   	int max_iov_size =
> >   		info->max_send_size - sizeof(struct smbd_data_transfer);
> @@
> > -2113,10 +2114,17 @@ int smbd_send(struct smbd_connection *info,
> struct smb_rqst *rqst)
> >   		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 set
> > +	 * rq_tailsz to PAGE_SIZE when the buffer has multiple pages and
> > +	 * ends at page boundary
> > +	 */
> >   	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
> > +			buflen += rqst->rq_pagesz * (rqst->rq_npages - 1) -
> > +					rqst->rq_offset + rqst->rq_tailsz;
> >   	}
> 
> This code is really confusing and redundant. It tests npages > 0, then tests
> npages == 1, then does an else. Why not call the helper like the following
> smbd_send()?

This code needs to get the combined length of all the pages in the request (but excluding iov, this is different to the function rqst_len in patch 05), but the following is for getting a single page from the request. 

I can simplify the code a little bit by following your suggestion in patch 05.

> 
> Tom.
> 
> >
> >   	if (buflen + sizeof(struct smbd_data_transfer) > @@ -2213,8 +2221,9
> > @@ int smbd_send(struct smbd_connection *info, struct smb_rqst *rqst)
> >
> >   	/* now sending pages if there are any */
> >   	for (i = 0; i < rqst->rq_npages; i++) {
> > -		buflen = (i == rqst->rq_npages-1) ?
> > -			rqst->rq_tailsz : rqst->rq_pagesz;
> > +		unsigned int offset;
> > +
> > +		rqst_page_get_length(rqst, i, &buflen, &offset);
> >   		nvecs = (buflen + max_iov_size - 1) / max_iov_size;
> >   		log_write(INFO, "sending pages buflen=%d nvecs=%d\n",
> >   			buflen, nvecs);
> > @@ -2225,9 +2234,11 @@ int smbd_send(struct smbd_connection *info,
> struct smb_rqst *rqst)
> >   			remaining_data_length -= size;
> >   			log_write(INFO, "sending pages i=%d offset=%d
> size=%d"
> >   				" remaining_data_length=%d\n",
> > -				i, j*max_iov_size, size,
> remaining_data_length);
> > +				i, j*max_iov_size+offset, size,
> > +				remaining_data_length);
> >   			rc = smbd_post_send_page(
> > -				info, rqst->rq_pages[i], j*max_iov_size,
> > +				info, rqst->rq_pages[i],
> > +				j*max_iov_size + offset,
> >   				size, remaining_data_length);
> >   			if (rc)
> >   				goto done;
> >