powerpc/83xx: add a const qualifier

[linux-2.6.git] / lib / scatterlist.c

/*
 * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
 *
 * Scatterlist handling helpers.
 *
 * This source code is licensed under the GNU General Public License,
 * Version 2. See the file COPYING for more details.
 */
#include <linux/export.h>
#include <linux/slab.h>
#include <linux/scatterlist.h>
#include <linux/highmem.h>
#include <linux/kmemleak.h>

/**
 * sg_next - return the next scatterlist entry in a list
 * @sg:         The current sg entry
 *
 * Description:
 *   Usually the next entry will be @sg@ + 1, but if this sg element is part
 *   of a chained scatterlist, it could jump to the start of a new
 *   scatterlist array.
 *
 **/
struct scatterlist *sg_next(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
        BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
        if (sg_is_last(sg))
                return NULL;

        sg++;
        if (unlikely(sg_is_chain(sg)))
                sg = sg_chain_ptr(sg);

        return sg;
}
EXPORT_SYMBOL(sg_next);

/**
 * sg_last - return the last scatterlist entry in a list
 * @sgl:        First entry in the scatterlist
 * @nents:      Number of entries in the scatterlist
 *
 * Description:
 *   Should only be used casually, it (currently) scans the entire list
 *   to get the last entry.
 *
 *   Note that the @sgl@ pointer passed in need not be the first one,
 *   the important bit is that @nents@ denotes the number of entries that
 *   exist from @sgl@.
 *
 **/
struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
{
#ifndef ARCH_HAS_SG_CHAIN
        struct scatterlist *ret = &sgl[nents - 1];
#else
        struct scatterlist *sg, *ret = NULL;
        unsigned int i;

        for_each_sg(sgl, sg, nents, i)
                ret = sg;

#endif
#ifdef CONFIG_DEBUG_SG
        BUG_ON(sgl[0].sg_magic != SG_MAGIC);
        BUG_ON(!sg_is_last(ret));
#endif
        return ret;
}
EXPORT_SYMBOL(sg_last);

/**
 * sg_init_table - Initialize SG table
 * @sgl:           The SG table
 * @nents:         Number of entries in table
 *
 * Notes:
 *   If this is part of a chained sg table, sg_mark_end() should be
 *   used only on the last table part.
 *
 **/
void sg_init_table(struct scatterlist *sgl, unsigned int nents)
{
        memset(sgl, 0, sizeof(*sgl) * nents);
#ifdef CONFIG_DEBUG_SG
        {
                unsigned int i;
                for (i = 0; i < nents; i++)
                        sgl[i].sg_magic = SG_MAGIC;
        }
#endif
        sg_mark_end(&sgl[nents - 1]);
}
EXPORT_SYMBOL(sg_init_table);

/**
 * sg_init_one - Initialize a single entry sg list
 * @sg:          SG entry
 * @buf:         Virtual address for IO
 * @buflen:      IO length
 *
 **/
void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
{
        sg_init_table(sg, 1);
        sg_set_buf(sg, buf, buflen);
}
EXPORT_SYMBOL(sg_init_one);

/*
 * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
 * helpers.
 */
static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
{
        if (nents == SG_MAX_SINGLE_ALLOC) {
                /*
                 * Kmemleak doesn't track page allocations as they are not
                 * commonly used (in a raw form) for kernel data structures.
                 * As we chain together a list of pages and then a normal
                 * kmalloc (tracked by kmemleak), in order to for that last
                 * allocation not to become decoupled (and thus a
                 * false-positive) we need to inform kmemleak of all the
                 * intermediate allocations.
                 */
                void *ptr = (void *) __get_free_page(gfp_mask);
                kmemleak_alloc(ptr, PAGE_SIZE, 1, gfp_mask);
                return ptr;
        } else
                return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
}

static void sg_kfree(struct scatterlist *sg, unsigned int nents)
{
        if (nents == SG_MAX_SINGLE_ALLOC) {
                kmemleak_free(sg);
                free_page((unsigned long) sg);
        } else
                kfree(sg);
}

/**
 * __sg_free_table - Free a previously mapped sg table
 * @table:      The sg table header to use
 * @max_ents:   The maximum number of entries per single scatterlist
 * @free_fn:    Free function
 *
 *  Description:
 *    Free an sg table previously allocated and setup with
 *    __sg_alloc_table().  The @max_ents value must be identical to
 *    that previously used with __sg_alloc_table().
 *
 **/
void __sg_free_table(struct sg_table *table, unsigned int max_ents,
                     sg_free_fn *free_fn)
{
        struct scatterlist *sgl, *next;

        if (unlikely(!table->sgl))
                return;

        sgl = table->sgl;
        while (table->orig_nents) {
                unsigned int alloc_size = table->orig_nents;
                unsigned int sg_size;

                /*
                 * If we have more than max_ents segments left,
                 * then assign 'next' to the sg table after the current one.
                 * sg_size is then one less than alloc size, since the last
                 * element is the chain pointer.
                 */
                if (alloc_size > max_ents) {
                        next = sg_chain_ptr(&sgl[max_ents - 1]);
                        alloc_size = max_ents;
                        sg_size = alloc_size - 1;
                } else {
                        sg_size = alloc_size;
                        next = NULL;
                }

                table->orig_nents -= sg_size;
                free_fn(sgl, alloc_size);
                sgl = next;
        }

        table->sgl = NULL;
}
EXPORT_SYMBOL(__sg_free_table);

/**
 * sg_free_table - Free a previously allocated sg table
 * @table:      The mapped sg table header
 *
 **/
void sg_free_table(struct sg_table *table)
{
        __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
}
EXPORT_SYMBOL(sg_free_table);

/**
 * __sg_alloc_table - Allocate and initialize an sg table with given allocator
 * @table:      The sg table header to use
 * @nents:      Number of entries in sg list
 * @max_ents:   The maximum number of entries the allocator returns per call
 * @gfp_mask:   GFP allocation mask
 * @alloc_fn:   Allocator to use
 *
 * Description:
 *   This function returns a @table @nents long. The allocator is
 *   defined to return scatterlist chunks of maximum size @max_ents.
 *   Thus if @nents is bigger than @max_ents, the scatterlists will be
 *   chained in units of @max_ents.
 *
 * Notes:
 *   If this function returns non-0 (eg failure), the caller must call
 *   __sg_free_table() to cleanup any leftover allocations.
 *
 **/
int __sg_alloc_table(struct sg_table *table, unsigned int nents,
                     unsigned int max_ents, gfp_t gfp_mask,
                     sg_alloc_fn *alloc_fn)
{
        struct scatterlist *sg, *prv;
        unsigned int left;

#ifndef ARCH_HAS_SG_CHAIN
        BUG_ON(nents > max_ents);
#endif

        memset(table, 0, sizeof(*table));

        left = nents;
        prv = NULL;
        do {
                unsigned int sg_size, alloc_size = left;

                if (alloc_size > max_ents) {
                        alloc_size = max_ents;
                        sg_size = alloc_size - 1;
                } else
                        sg_size = alloc_size;

                left -= sg_size;

                sg = alloc_fn(alloc_size, gfp_mask);
                if (unlikely(!sg)) {
                        /*
                         * Adjust entry count to reflect that the last
                         * entry of the previous table won't be used for
                         * linkage.  Without this, sg_kfree() may get
                         * confused.
                         */
                        if (prv)
                                table->nents = ++table->orig_nents;

                        return -ENOMEM;
                }

                sg_init_table(sg, alloc_size);
                table->nents = table->orig_nents += sg_size;

                /*
                 * If this is the first mapping, assign the sg table header.
                 * If this is not the first mapping, chain previous part.
                 */
                if (prv)
                        sg_chain(prv, max_ents, sg);
                else
                        table->sgl = sg;

                /*
                 * If no more entries after this one, mark the end
                 */
                if (!left)
                        sg_mark_end(&sg[sg_size - 1]);

                prv = sg;
        } while (left);

        return 0;
}
EXPORT_SYMBOL(__sg_alloc_table);

/**
 * sg_alloc_table - Allocate and initialize an sg table
 * @table:      The sg table header to use
 * @nents:      Number of entries in sg list
 * @gfp_mask:   GFP allocation mask
 *
 *  Description:
 *    Allocate and initialize an sg table. If @nents@ is larger than
 *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
 *
 **/
int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
{
        int ret;

        ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
                               gfp_mask, sg_kmalloc);
        if (unlikely(ret))
                __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);

        return ret;
}
EXPORT_SYMBOL(sg_alloc_table);

/**
 * sg_alloc_table_from_pages - Allocate and initialize an sg table from
 *                             an array of pages
 * @sgt:        The sg table header to use
 * @pages:      Pointer to an array of page pointers
 * @n_pages:    Number of pages in the pages array
 * @offset:     Offset from start of the first page to the start of a buffer
 * @size:       Number of valid bytes in the buffer (after offset)
 * @gfp_mask:   GFP allocation mask
 *
 *  Description:
 *    Allocate and initialize an sg table from a list of pages. Contiguous
 *    ranges of the pages are squashed into a single scatterlist node. A user
 *    may provide an offset at a start and a size of valid data in a buffer
 *    specified by the page array. The returned sg table is released by
 *    sg_free_table.
 *
 * Returns:
 *   0 on success, negative error on failure
 */
int sg_alloc_table_from_pages(struct sg_table *sgt,
        struct page **pages, unsigned int n_pages,
        unsigned long offset, unsigned long size,
        gfp_t gfp_mask)
{
        unsigned int chunks;
        unsigned int i;
        unsigned int cur_page;
        int ret;
        struct scatterlist *s;

        /* compute number of contiguous chunks */
        chunks = 1;
        for (i = 1; i < n_pages; ++i)
                if (page_to_pfn(pages[i]) != page_to_pfn(pages[i - 1]) + 1)
                        ++chunks;

        ret = sg_alloc_table(sgt, chunks, gfp_mask);
        if (unlikely(ret))
                return ret;

        /* merging chunks and putting them into the scatterlist */
        cur_page = 0;
        for_each_sg(sgt->sgl, s, sgt->orig_nents, i) {
                unsigned long chunk_size;
                unsigned int j;

                /* look for the end of the current chunk */
                for (j = cur_page + 1; j < n_pages; ++j)
                        if (page_to_pfn(pages[j]) !=
                            page_to_pfn(pages[j - 1]) + 1)
                                break;

                chunk_size = ((j - cur_page) << PAGE_SHIFT) - offset;
                sg_set_page(s, pages[cur_page], min(size, chunk_size), offset);
                size -= chunk_size;
                offset = 0;
                cur_page = j;
        }

        return 0;
}
EXPORT_SYMBOL(sg_alloc_table_from_pages);

/**
 * sg_miter_start - start mapping iteration over a sg list
 * @miter: sg mapping iter to be started
 * @sgl: sg list to iterate over
 * @nents: number of sg entries
 *
 * Description:
 *   Starts mapping iterator @miter.
 *
 * Context:
 *   Don't care.
 */
void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
                    unsigned int nents, unsigned int flags)
{
        memset(miter, 0, sizeof(struct sg_mapping_iter));

        miter->__sg = sgl;
        miter->__nents = nents;
        miter->__offset = 0;
        WARN_ON(!(flags & (SG_MITER_TO_SG | SG_MITER_FROM_SG)));
        miter->__flags = flags;
}
EXPORT_SYMBOL(sg_miter_start);

/**
 * sg_miter_next - proceed mapping iterator to the next mapping
 * @miter: sg mapping iter to proceed
 *
 * Description:
 *   Proceeds @miter@ to the next mapping.  @miter@ should have been
 *   started using sg_miter_start().  On successful return,
 *   @miter@->page, @miter@->addr and @miter@->length point to the
 *   current mapping.
 *
 * Context:
 *   IRQ disabled if SG_MITER_ATOMIC.  IRQ must stay disabled till
 *   @miter@ is stopped.  May sleep if !SG_MITER_ATOMIC.
 *
 * Returns:
 *   true if @miter contains the next mapping.  false if end of sg
 *   list is reached.
 */
bool sg_miter_next(struct sg_mapping_iter *miter)
{
        unsigned int off, len;

        /* check for end and drop resources from the last iteration */
        if (!miter->__nents)
                return false;

        sg_miter_stop(miter);

        /* get to the next sg if necessary.  __offset is adjusted by stop */
        while (miter->__offset == miter->__sg->length) {
                if (--miter->__nents) {
                        miter->__sg = sg_next(miter->__sg);
                        miter->__offset = 0;
                } else
                        return false;
        }

        /* map the next page */
        off = miter->__sg->offset + miter->__offset;
        len = miter->__sg->length - miter->__offset;

        miter->page = nth_page(sg_page(miter->__sg), off >> PAGE_SHIFT);
        off &= ~PAGE_MASK;
        miter->length = min_t(unsigned int, len, PAGE_SIZE - off);
        miter->consumed = miter->length;

        if (miter->__flags & SG_MITER_ATOMIC)
                miter->addr = kmap_atomic(miter->page) + off;
        else
                miter->addr = kmap(miter->page) + off;

        return true;
}
EXPORT_SYMBOL(sg_miter_next);

/**
 * sg_miter_stop - stop mapping iteration
 * @miter: sg mapping iter to be stopped
 *
 * Description:
 *   Stops mapping iterator @miter.  @miter should have been started
 *   started using sg_miter_start().  A stopped iteration can be
 *   resumed by calling sg_miter_next() on it.  This is useful when
 *   resources (kmap) need to be released during iteration.
 *
 * Context:
 *   IRQ disabled if the SG_MITER_ATOMIC is set.  Don't care otherwise.
 */
void sg_miter_stop(struct sg_mapping_iter *miter)
{
        WARN_ON(miter->consumed > miter->length);

        /* drop resources from the last iteration */
        if (miter->addr) {
                miter->__offset += miter->consumed;

                if (miter->__flags & SG_MITER_TO_SG)
                        flush_kernel_dcache_page(miter->page);

                if (miter->__flags & SG_MITER_ATOMIC) {
                        WARN_ON(!irqs_disabled());
                        kunmap_atomic(miter->addr);
                } else
                        kunmap(miter->page);

                miter->page = NULL;
                miter->addr = NULL;
                miter->length = 0;
                miter->consumed = 0;
        }
}
EXPORT_SYMBOL(sg_miter_stop);

/**
 * sg_copy_buffer - Copy data between a linear buffer and an SG list
 * @sgl:                 The SG list
 * @nents:               Number of SG entries
 * @buf:                 Where to copy from
 * @buflen:              The number of bytes to copy
 * @to_buffer:           transfer direction (non zero == from an sg list to a
 *                       buffer, 0 == from a buffer to an sg list
 *
 * Returns the number of copied bytes.
 *
 **/
static size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents,
                             void *buf, size_t buflen, int to_buffer)
{
        unsigned int offset = 0;
        struct sg_mapping_iter miter;
        unsigned long flags;
        unsigned int sg_flags = SG_MITER_ATOMIC;

        if (to_buffer)
                sg_flags |= SG_MITER_FROM_SG;
        else
                sg_flags |= SG_MITER_TO_SG;

        sg_miter_start(&miter, sgl, nents, sg_flags);

        local_irq_save(flags);

        while (sg_miter_next(&miter) && offset < buflen) {
                unsigned int len;

                len = min(miter.length, buflen - offset);

                if (to_buffer)
                        memcpy(buf + offset, miter.addr, len);
                else
                        memcpy(miter.addr, buf + offset, len);

                offset += len;
        }

        sg_miter_stop(&miter);

        local_irq_restore(flags);
        return offset;
}

/**
 * sg_copy_from_buffer - Copy from a linear buffer to an SG list
 * @sgl:                 The SG list
 * @nents:               Number of SG entries
 * @buf:                 Where to copy from
 * @buflen:              The number of bytes to copy
 *
 * Returns the number of copied bytes.
 *
 **/
size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
                           void *buf, size_t buflen)
{
        return sg_copy_buffer(sgl, nents, buf, buflen, 0);
}
EXPORT_SYMBOL(sg_copy_from_buffer);

/**
 * sg_copy_to_buffer - Copy from an SG list to a linear buffer
 * @sgl:                 The SG list
 * @nents:               Number of SG entries
 * @buf:                 Where to copy to
 * @buflen:              The number of bytes to copy
 *
 * Returns the number of copied bytes.
 *
 **/
size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
                         void *buf, size_t buflen)
{
        return sg_copy_buffer(sgl, nents, buf, buflen, 1);
}
EXPORT_SYMBOL(sg_copy_to_buffer);