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SubjectRe: [PATCH 1/2] memstick: add support for legacy memorysticks
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On Thu, 2010-12-09 at 13:09 -0800, Andrew Morton wrote:
> On Thu, 9 Dec 2010 04:42:25 +0200
> Maxim Levitsky <maximlevitsky@gmail.com> wrote:
>
> > +/*
> > + * Advance scatterlist by 'consumed' bytes
> > + * Returns new scatterlist, or NULL if can't advance that much
> > + */
> > +static struct scatterlist *sg_advance(struct scatterlist *sg, int consumed)
> > +{
> > + while (consumed >= sg->length) {
> > + consumed -= sg->length;
> > +
> > + sg = sg_next(sg);
> > + if (!sg)
> > + break;
> > + }
> > +
> > + WARN_ON(!sg && consumed);
> > +
> > + if (!sg)
> > + return NULL;
> > +
> > + sg->offset += consumed;
> > + sg->length -= consumed;
> > +
> > + if (sg->offset >= PAGE_SIZE) {
> > + struct page *page =
> > + nth_page(sg_page(sg), sg->offset / PAGE_SIZE);
> > + sg_set_page(sg, page, sg->length, sg->offset % PAGE_SIZE);
> > + }
> > +
> > + return sg;
> > +}
> > +
> > +/* Calculate number of sg entries in sg list */
> > +static int sg_nents(struct scatterlist *sg)
> > +{
> > + int nents = 0;
> > + while (sg) {
> > + nents++;
> > + sg = sg_next(sg);
> > + }
> > +
> > + return nents;
> > +}
> > +
> > +/* Calculate total lenght of scatterlist */
>
> (typo)
>
> > +static int sg_total_len(struct scatterlist *sg)
> > +{
> > + int len = 0;
> > + while (sg) {
> > + len += sg->length;
> > + sg = sg_next(sg);
> > + }
> > + return len;
> > +}
> > +
> > +/* Compare contents of an sg to a buffer */
> > +static bool sg_compare_to_buffer(struct scatterlist *sg, u8 *buffer, size_t len)
> > +{
> > + unsigned long flags;
> > + int retval = 0;
> > + struct sg_mapping_iter miter;
> > +
> > + if (sg_total_len(sg) < len)
> > + return 1;
> > +
> > + local_irq_save(flags);
> > + sg_miter_start(&miter, sg, sg_nents(sg),
> > + SG_MITER_ATOMIC | SG_MITER_FROM_SG);
> > +
> > + while (sg_miter_next(&miter) && len > 0) {
> > +
> > + int cmplen = min(miter.length, len);
> > + if (memcmp(miter.addr, buffer, cmplen)) {
> > + retval = 1;
> > + break;
> > + }
> > +
> > + buffer += cmplen;
> > + len -= cmplen;
> > + }
> > +
> > + sg_miter_stop(&miter);
> > + local_irq_restore(flags);
> > + return retval;
> > +}
>
> I think I mentioned this before, but ... it's really bad that the
> above functions appear in a particular device driver. They are, to
> varying degrees, independent of that driver and should be provided by
> the sglist core code.
I agree with you.
However, note that Alex's mspro_blk.c, also contains the above logic, it
is just not separated from the code.
I don't mind adding these to scatterlist code.



>
> Also, the local_irq_save/restore in sg_compare_to_buffer() is quite
> mysterious and should have a comment explaining why it is there. Once
> that's done, I might understand why it isn't a bug on SMP machines ;)
Its is done to be able to use kmap_atomic.
I think I can use sg_mitter there, I will try to.

Best regards,
Maxim Levitsky.






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