cregit-Linux how code gets into the kernel

Release 4.11 drivers/misc/cb710/sgbuf2.c

/*
 *  cb710/sgbuf2.c
 *
 *  Copyright by Michał Mirosław, 2008-2009
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation.
 */
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/cb710.h>


static bool sg_dwiter_next(struct sg_mapping_iter *miter) { if (sg_miter_next(miter)) { miter->consumed = 0; return true; } else return false; }

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static bool sg_dwiter_is_at_end(struct sg_mapping_iter *miter) { return miter->length == miter->consumed && !sg_dwiter_next(miter); }

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static uint32_t sg_dwiter_read_buffer(struct sg_mapping_iter *miter) { size_t len, left = 4; uint32_t data; void *addr = &data; do { len = min(miter->length - miter->consumed, left); memcpy(addr, miter->addr + miter->consumed, len); miter->consumed += len; left -= len; if (!left) return data; addr += len; } while (sg_dwiter_next(miter)); memset(addr, 0, left); return data; }

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static inline bool needs_unaligned_copy(const void *ptr) { #ifdef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS return false; #else return ((ptr - NULL) & 3) != 0; #endif }

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static bool sg_dwiter_get_next_block(struct sg_mapping_iter *miter, uint32_t **ptr) { size_t len; if (sg_dwiter_is_at_end(miter)) return true; len = miter->length - miter->consumed; if (likely(len >= 4 && !needs_unaligned_copy( miter->addr + miter->consumed))) { *ptr = miter->addr + miter->consumed; miter->consumed += 4; return true; } return false; }

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/** * cb710_sg_dwiter_read_next_block() - get next 32-bit word from sg buffer * @miter: sg mapping iterator used for reading * * Description: * Returns 32-bit word starting at byte pointed to by @miter@ * handling any alignment issues. Bytes past the buffer's end * are not accessed (read) but are returned as zeroes. @miter@ * is advanced by 4 bytes or to the end of buffer whichever is * closer. * * Context: * Same requirements as in sg_miter_next(). * * Returns: * 32-bit word just read. */
uint32_t cb710_sg_dwiter_read_next_block(struct sg_mapping_iter *miter) { uint32_t *ptr = NULL; if (likely(sg_dwiter_get_next_block(miter, &ptr))) return ptr ? *ptr : 0; return sg_dwiter_read_buffer(miter); }

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EXPORT_SYMBOL_GPL(cb710_sg_dwiter_read_next_block);
static void sg_dwiter_write_slow(struct sg_mapping_iter *miter, uint32_t data) { size_t len, left = 4; void *addr = &data; do { len = min(miter->length - miter->consumed, left); memcpy(miter->addr, addr, len); miter->consumed += len; left -= len; if (!left) return; addr += len; } while (sg_dwiter_next(miter)); }

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/** * cb710_sg_dwiter_write_next_block() - write next 32-bit word to sg buffer * @miter: sg mapping iterator used for writing * * Description: * Writes 32-bit word starting at byte pointed to by @miter@ * handling any alignment issues. Bytes which would be written * past the buffer's end are silently discarded. @miter@ is * advanced by 4 bytes or to the end of buffer whichever is closer. * * Context: * Same requirements as in sg_miter_next(). */
void cb710_sg_dwiter_write_next_block(struct sg_mapping_iter *miter, uint32_t data) { uint32_t *ptr = NULL; if (likely(sg_dwiter_get_next_block(miter, &ptr))) { if (ptr) *ptr = data; else return; } else sg_dwiter_write_slow(miter, data); }

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EXPORT_SYMBOL_GPL(cb710_sg_dwiter_write_next_block);

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