On Wed, 12 Mar 2008, FUJITA Tomonori wrote:
> It enables us to simplify usb_stor_access_xfer_buf like this, I think
> (it's not tested).
>
> diff --git a/drivers/usb/storage/protocol.c b/drivers/usb/storage/protocol.c
> index b9b8ede..0992809 100644
> --- a/drivers/usb/storage/protocol.c
> +++ b/drivers/usb/storage/protocol.c
> @@ -156,70 +156,11 @@ unsigned int usb_stor_access_xfer_buf(unsigned char *buffer,
> unsigned int buflen, struct scsi_cmnd *srb, struct scatterlist **sgptr,
> unsigned int *offset, enum xfer_buf_dir dir)
> {
> - unsigned int cnt;
> - struct scatterlist *sg = *sgptr;
> -
> - /* We have to go through the list one entry
> - * at a time. Each s-g entry contains some number of pages, and
> - * each page has to be kmap()'ed separately. If the page is already
> - * in kernel-addressable memory then kmap() will return its address.
> - * If the page is not directly accessible -- such as a user buffer
> - * located in high memory -- then kmap() will map it to a temporary
> - * position in the kernel's virtual address space.
> - */
> -
> - if (!sg)
> - sg = scsi_sglist(srb);
> + if (!*sgptr)
> + *sgptr = scsi_sglist(srb);
>
> - /* This loop handles a single s-g list entry, which may
> - * include multiple pages. Find the initial page structure
> - * and the starting offset within the page, and update
> - * the *offset and **sgptr values for the next loop.
> - */
> - cnt = 0;
> - while (cnt < buflen && sg) {
> - struct page *page = sg_page(sg) +
> - ((sg->offset + *offset) >> PAGE_SHIFT);
> - unsigned int poff = (sg->offset + *offset) & (PAGE_SIZE-1);
> - unsigned int sglen = sg->length - *offset;
> -
> - if (sglen > buflen - cnt) {
> -
> - /* Transfer ends within this s-g entry */
> - sglen = buflen - cnt;
> - *offset += sglen;
> - } else {
> -
> - /* Transfer continues to next s-g entry */
> - *offset = 0;
> - sg = sg_next(sg);
> - }
> -
> - /* Transfer the data for all the pages in this
> - * s-g entry. For each page: call kmap(), do the
> - * transfer, and call kunmap() immediately after. */
> - while (sglen > 0) {
> - unsigned int plen = min(sglen, (unsigned int)
> - PAGE_SIZE - poff);
> - unsigned char *ptr = kmap(page);
> -
> - if (dir == TO_XFER_BUF)
> - memcpy(ptr + poff, buffer + cnt, plen);
> - else
> - memcpy(buffer + cnt, ptr + poff, plen);
> - kunmap(page);
> -
> - /* Start at the beginning of the next page */
> - poff = 0;
> - ++page;
> - cnt += plen;
> - sglen -= plen;
> - }
> - }
> - *sgptr = sg;
> -
> - /* Return the amount actually transferred */
> - return cnt;
> + return sg_copy_buffer(sgptr, scsi_sg_count(srb),
> + offset, buffer, buflen, dir != TO_XFER_BUF);
> }
It's a big simplification!
There are two problems. One is the types of the arguments and return
value. The other is that local interrupts need to be disabled.
Alan Stern
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