scatterlist.h

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#ifndef _LINUX_SCATTERLIST_H
#define _LINUX_SCATTERLIST_H

#include <linux/string.h>
#include <linux/bug.h>
#include <linux/mm.h>

#include <asm/types.h>
#include <asm/scatterlist.h>
#include <asm/io.h>

struct sg_table {
    struct scatterlist *sgl;    /* the list */
    unsigned int nents;     /* number of mapped entries */
    unsigned int orig_nents;    /* original size of list */
};

/*
 * Notes on SG table design.
 *
 * Architectures must provide an unsigned long page_link field in the
 * scatterlist struct. We use that to place the page pointer AND encode
 * information about the sg table as well. The two lower bits are reserved
 * for this information.
 *
 * If bit 0 is set, then the page_link contains a pointer to the next sg
 * table list. Otherwise the next entry is at sg + 1.
 *
 * If bit 1 is set, then this sg entry is the last element in a list.
 *
 * See sg_next().
 *
 */

#define SG_MAGIC    0x87654321

/*
 * We overload the LSB of the page pointer to indicate whether it's
 * a valid sg entry, or whether it points to the start of a new scatterlist.
 * Those low bits are there for everyone! (thanks mason :-)
 */
#define sg_is_chain(sg)     ((sg)->page_link & 0x01)
#define sg_is_last(sg)      ((sg)->page_link & 0x02)
#define sg_chain_ptr(sg)    \
    ((struct scatterlist *) ((sg)->page_link & ~0x03))

static inline void sg_assign_page(struct scatterlist *sg, struct page *page)
{
    unsigned long page_link = sg->page_link & 0x3;

    /*
     * In order for the low bit stealing approach to work, pages
     * must be aligned at a 32-bit boundary as a minimum.
     */
    BUG_ON((unsigned long) page & 0x03);
#ifdef CONFIG_DEBUG_SG
    BUG_ON(sg->sg_magic != SG_MAGIC);
    BUG_ON(sg_is_chain(sg));
#endif
    sg->page_link = page_link | (unsigned long) page;
}

static inline void sg_set_page(struct scatterlist *sg, struct page *page,
                   unsigned int len, unsigned int offset)
{
    sg_assign_page(sg, page);
    sg->offset = offset;
    sg->length = len;
}

static inline struct page *sg_page(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
    BUG_ON(sg->sg_magic != SG_MAGIC);
    BUG_ON(sg_is_chain(sg));
#endif
    return (struct page *)((sg)->page_link & ~0x3);
}

static inline void sg_set_buf(struct scatterlist *sg, const void *buf,
                  unsigned int buflen)
{
    sg_set_page(sg, virt_to_page(buf), buflen, offset_in_page(buf));
}

/*
 * Loop over each sg element, following the pointer to a new list if necessary
 */
#define for_each_sg(sglist, sg, nr, __i)    \
    for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg))

static inline void sg_chain(struct scatterlist *prv, unsigned int prv_nents,
                struct scatterlist *sgl)
{
#ifndef ARCH_HAS_SG_CHAIN
    BUG();
#endif

    /*
     * offset and length are unused for chain entry.  Clear them.
     */
    prv[prv_nents - 1].offset = 0;
    prv[prv_nents - 1].length = 0;

    /*
     * Set lowest bit to indicate a link pointer, and make sure to clear
     * the termination bit if it happens to be set.
     */
    prv[prv_nents - 1].page_link = ((unsigned long) sgl | 0x01) & ~0x02;
}

static inline void sg_mark_end(struct scatterlist *sg)
{
#ifdef CONFIG_DEBUG_SG
    BUG_ON(sg->sg_magic != SG_MAGIC);
#endif
    /*
     * Set termination bit, clear potential chain bit
     */
    sg->page_link |= 0x02;
    sg->page_link &= ~0x01;
}

static inline dma_addr_t sg_phys(struct scatterlist *sg)
{
    return page_to_phys(sg_page(sg)) + sg->offset;
}

static inline void *sg_virt(struct scatterlist *sg)
{
    return page_address(sg_page(sg)) + sg->offset;
}

int sg_nents(struct scatterlist *sg);
struct scatterlist *sg_next(struct scatterlist *);
struct scatterlist *sg_last(struct scatterlist *s, unsigned int);
void sg_init_table(struct scatterlist *, unsigned int);
void sg_init_one(struct scatterlist *, const void *, unsigned int);

typedef struct scatterlist *(sg_alloc_fn)(unsigned int, gfp_t);
typedef void (sg_free_fn)(struct scatterlist *, unsigned int);

void __sg_free_table(struct sg_table *, unsigned int, sg_free_fn *);
void sg_free_table(struct sg_table *);
int __sg_alloc_table(struct sg_table *, unsigned int, unsigned int, gfp_t,
             sg_alloc_fn *);
int sg_alloc_table(struct sg_table *, unsigned int, gfp_t);
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);

size_t sg_copy_from_buffer(struct scatterlist *sgl, unsigned int nents,
               void *buf, size_t buflen);
size_t sg_copy_to_buffer(struct scatterlist *sgl, unsigned int nents,
             void *buf, size_t buflen);

/*
 * Maximum number of entries that will be allocated in one piece, if
 * a list larger than this is required then chaining will be utilized.
 */
#define SG_MAX_SINGLE_ALLOC     (PAGE_SIZE / sizeof(struct scatterlist))


/*
 * Mapping sg iterator
 *
 * Iterates over sg entries mapping page-by-page.  On each successful
 * iteration, @miter->page points to the mapped page and
 * @miter->length bytes of data can be accessed at @miter->addr.  As
 * long as an interation is enclosed between start and stop, the user
 * is free to choose control structure and when to stop.
 *
 * @miter->consumed is set to @miter->length on each iteration.  It
 * can be adjusted if the user can't consume all the bytes in one go.
 * Also, a stopped iteration can be resumed by calling next on it.
 * This is useful when iteration needs to release all resources and
 * continue later (e.g. at the next interrupt).
 */

#define SG_MITER_ATOMIC     (1 << 0)     /* use kmap_atomic */
#define SG_MITER_TO_SG      (1 << 1)    /* flush back to phys on unmap */
#define SG_MITER_FROM_SG    (1 << 2)    /* nop */

struct sg_mapping_iter {
    /* the following three fields can be accessed directly */
    struct page     *page;      /* currently mapped page */
    void            *addr;      /* pointer to the mapped area */
    size_t          length;     /* length of the mapped area */
    size_t          consumed;   /* number of consumed bytes */

    /* these are internal states, keep away */
    struct scatterlist  *__sg;      /* current entry */
    unsigned int        __nents;    /* nr of remaining entries */
    unsigned int        __offset;   /* offset within sg */
    unsigned int        __flags;
};

void sg_miter_start(struct sg_mapping_iter *miter, struct scatterlist *sgl,
            unsigned int nents, unsigned int flags);
bool sg_miter_next(struct sg_mapping_iter *miter);
void sg_miter_stop(struct sg_mapping_iter *miter);

#endif /* _LINUX_SCATTERLIST_H */