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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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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.

Tom.

> }
>
> return buflen;
>

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