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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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