linux scatterlist阅读三

sg_copy_buffer

函数定义：

/*** 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* @skip:		 Number of bytes to skip before copying* @to_buffer:		 transfer direction (true == from an sg list to a*			 buffer, false == from a buffer to an sg list** Returns the number of copied bytes.***/
size_t sg_copy_buffer(struct scatterlist *sgl, unsigned int nents, void *buf, size_t buflen, off_t skip, bool to_buffer)
{unsigned int offset = 0;struct sg_mapping_iter miter;unsigned int sg_flags = SG_MITER_ATOMIC;if (to_buffer)sg_flags |= SG_MITER_FROM_SG;elsesg_flags |= SG_MITER_TO_SG;sg_miter_start(&miter, sgl, nents, sg_flags);if (!sg_miter_skip(&miter, skip))return false;while ((offset < buflen) && sg_miter_next(&miter)) {unsigned int len;len = min(miter.length, buflen - offset);if (to_buffer)memcpy(buf + offset, miter.addr, len);elsememcpy(miter.addr, buf + offset, len);offset += len;}sg_miter_stop(&miter);return offset;
}
EXPORT_SYMBOL(sg_copy_buffer);

函数实现比较复杂，还涉及了struct sg_mapping_iter 结构体，这里比较重要的是skip参数，是指拷贝时跳过的字节数。

sg_copy_from_buffer

函数定义：

/*** 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,const void *buf, size_t buflen)
{return sg_copy_buffer(sgl, nents, (void *)buf, buflen, 0, false);
}
EXPORT_SYMBOL(sg_copy_from_buffer);

从buf缓冲区里拷贝buflen长度的数据到sgl表里，返回值是成功拷贝到字节数

sg_copy_to_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, 0, true);
}
EXPORT_SYMBOL(sg_copy_to_buffer);

sg_pcopy_from_buffer

/*** sg_pcopy_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* @skip:		 Number of bytes to skip before copying** Returns the number of copied bytes.***/
size_t sg_pcopy_from_buffer(struct scatterlist *sgl, unsigned int nents, const void *buf, size_t buflen, off_t skip)
{return sg_copy_buffer(sgl, nents, (void *)buf, buflen, skip, false);
}
EXPORT_SYMBOL(sg_pcopy_from_buffer);

sg_pcopy_to_buffer

/*** sg_pcopy_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* @skip:		 Number of bytes to skip before copying** Returns the number of copied bytes.***/
size_t sg_pcopy_to_buffer(struct scatterlist *sgl, unsigned int nents,void *buf, size_t buflen, off_t skip)
{return sg_copy_buffer(sgl, nents, buf, buflen, skip, true);
}
EXPORT_SYMBOL(sg_pcopy_to_buffer);

sg_zero_buffer

把skip后面的数据清0，比如sgl里面的数据是"abcde",skip等于2，调用函数以后，sgl里面的数据是"ab"

/*** sg_zero_buffer - Zero-out a part of a SG list* @sgl:		 The SG list* @nents:		 Number of SG entries* @buflen:		 The number of bytes to zero out* @skip:		 Number of bytes to skip before zeroing** Returns the number of bytes zeroed.**/
size_t sg_zero_buffer(struct scatterlist *sgl, unsigned int nents,size_t buflen, off_t skip)
{unsigned int offset = 0;struct sg_mapping_iter miter;unsigned int sg_flags = SG_MITER_ATOMIC | SG_MITER_TO_SG;sg_miter_start(&miter, sgl, nents, sg_flags);if (!sg_miter_skip(&miter, skip))return false;while (offset < buflen && sg_miter_next(&miter)) {unsigned int len;len = min(miter.length, buflen - offset);memset(miter.addr, 0, len);offset += len;}sg_miter_stop(&miter);return offset;
}
EXPORT_SYMBOL(sg_zero_buffer);

最后来个demo，看看怎么使用。

#include <linux/types.h>
#include <linux/fcntl.h>
#include <linux/hdreg.h>
#include <linux/genhd.h>
#include <linux/blkdev.h>
#include <linux/scatterlist.h>//struct sg_table sgt;struct scatterlist *sgl;
void *buf;/* 驱动出口函数 */
static int __init ramdisk_init(void)
{int i;void *buffer;struct scatterlist *sg;printk("sg init\n");sgl = (struct scatterlist *)kmalloc(sizeof(struct scatterlist) * 1, GFP_KERNEL);if(!sgl)return -1;buf = kmalloc(1000, GFP_KERNEL);if(!buf)return -1;buffer = kmalloc(100, GFP_KERNEL);if(!buffer)return -1;memset(buffer, 0, 100);memcpy(buffer, "hello world", 12);void *p;sg_init_one(sgl, buf, 1000);for_each_sg(sgl, sg, 1, i) {//sg_pcopy_from_buffer(sg, 1, buffer, 100, 5);sg_copy_from_buffer(sg, 1, buffer, 100);p = sg_virt(sg);//p = p + 5;printk("p = %s\n", (char *)p);memset(buffer, 0, 100);sg_pcopy_to_buffer(sg, 1, buffer, 100, 6);printk("buffer = %s\n", (char *)buffer);}kfree(buffer);return 0;
}/* 驱动出口函数 */
static void __exit ramdisk_exit(void)
{printk("sg exit\n");kfree(buf);kfree(sgl);
}module_init(ramdisk_init);
module_exit(ramdisk_exit);