root/include/linux/uio.h

INCLUDED FROM

DEFINITIONS

1. iov_length
2. iov_iter_iovec
3. iov_iter_count
4. iov_iter_truncate
5. iov_iter_reexpand

/*
 *      Berkeley style UIO structures   -       Alan Cox 1994.
 *
 *              This program is free software; you can redistribute it and/or
 *              modify it under the terms of the GNU General Public License
 *              as published by the Free Software Foundation; either version
 *              2 of the License, or (at your option) any later version.
 */
#ifndef __LINUX_UIO_H
#define __LINUX_UIO_H

#include <linux/kernel.h>
#include <uapi/linux/uio.h>

struct page;

struct kvec {
        void *iov_base; /* and that should *never* hold a userland pointer */
        size_t iov_len;
};

enum {
        ITER_IOVEC = 0,
        ITER_KVEC = 2,
        ITER_BVEC = 4,
};

struct iov_iter {
        int type;
        size_t iov_offset;
        size_t count;
        union {
                const struct iovec *iov;
                const struct bio_vec *bvec;
        };
        unsigned long nr_segs;
};

/*
 * Total number of bytes covered by an iovec.
 *
 * NOTE that it is not safe to use this function until all the iovec's
 * segment lengths have been validated.  Because the individual lengths can
 * overflow a size_t when added together.
 */
static inline size_t iov_length(const struct iovec *iov, unsigned long nr_segs)
{
        unsigned long seg;
        size_t ret = 0;

        for (seg = 0; seg < nr_segs; seg++)
                ret += iov[seg].iov_len;
        return ret;
}

static inline struct iovec iov_iter_iovec(const struct iov_iter *iter)
{
        return (struct iovec) {
                .iov_base = iter->iov->iov_base + iter->iov_offset,
                .iov_len = min(iter->count,
                               iter->iov->iov_len - iter->iov_offset),
        };
}

#define iov_for_each(iov, iter, start)                          \
        if (!((start).type & ITER_BVEC))                        \
        for (iter = (start);                                    \
             (iter).count &&                                    \
             ((iov = iov_iter_iovec(&(iter))), 1);              \
             iov_iter_advance(&(iter), (iov).iov_len))

unsigned long iov_shorten(struct iovec *iov, unsigned long nr_segs, size_t to);

size_t iov_iter_copy_from_user_atomic(struct page *page,
                struct iov_iter *i, unsigned long offset, size_t bytes);
void iov_iter_advance(struct iov_iter *i, size_t bytes);
int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes);
size_t iov_iter_single_seg_count(const struct iov_iter *i);
size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i);
size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
                         struct iov_iter *i);
size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i);
size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i);
size_t iov_iter_zero(size_t bytes, struct iov_iter *);
unsigned long iov_iter_alignment(const struct iov_iter *i);
void iov_iter_init(struct iov_iter *i, int direction, const struct iovec *iov,
                        unsigned long nr_segs, size_t count);
ssize_t iov_iter_get_pages(struct iov_iter *i, struct page **pages,
                        size_t maxsize, unsigned maxpages, size_t *start);
ssize_t iov_iter_get_pages_alloc(struct iov_iter *i, struct page ***pages,
                        size_t maxsize, size_t *start);
int iov_iter_npages(const struct iov_iter *i, int maxpages);

static inline size_t iov_iter_count(struct iov_iter *i)
{
        return i->count;
}

/*
 * Cap the iov_iter by given limit; note that the second argument is
 * *not* the new size - it's upper limit for such.  Passing it a value
 * greater than the amount of data in iov_iter is fine - it'll just do
 * nothing in that case.
 */
static inline void iov_iter_truncate(struct iov_iter *i, u64 count)
{
        /*
         * count doesn't have to fit in size_t - comparison extends both
         * operands to u64 here and any value that would be truncated by
         * conversion in assignement is by definition greater than all
         * values of size_t, including old i->count.
         */
        if (i->count > count)
                i->count = count;
}

/*
 * reexpand a previously truncated iterator; count must be no more than how much
 * we had shrunk it.
 */
static inline void iov_iter_reexpand(struct iov_iter *i, size_t count)
{
        i->count = count;
}

int memcpy_fromiovec(unsigned char *kdata, struct iovec *iov, int len);
int memcpy_toiovec(struct iovec *iov, unsigned char *kdata, int len);
int memcpy_fromiovecend(unsigned char *kdata, const struct iovec *iov,
                        int offset, int len);
int memcpy_toiovecend(const struct iovec *v, unsigned char *kdata,
                      int offset, int len);

#endif