linux内核将块设备相关的驱动放在drivers/block路径下：
root@zhengyang:/work/sambashare/linux-5.2.8# ls drivers/block/ amiflop.c built-in.a loop.c nbd.c pktcdvd.c rsxx swim_asm.S virtio_blk.c zram aoe cryptoloop.c loop.h null_blk.h ps3disk.c skd_main.c swim.c xen-blkback ataflop.c drbd loop.o null_blk_main.c ps3vram.c skd_s1120.h sx8.c xen-blkfront.c brd.c floppy.c Makefile null_blk_zoned.c rbd.c sunvdc.c umem.c xsysace.c brd.o Kconfig mtip32xx paride rbd_types.h swim3.c umem.h z2ram.c
这里我们以块设备驱动z2ram为例进行讲解分析。z2ram驱动是实用RAM模拟一段块设备，也就是ramdisk。
一、全局变量
z2ram块设备驱动的实现位于drivers/block/z2ram.c，在文件的开始定义了全局变量：
#define DEVICE_NAME "Z2RAM"
#include <linux/major.h>
#include <linux/vmalloc.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/blk-mq.h>
#include <linux/bitops.h>
#include <linux/mutex.h>
#include <linux/slab.h>
#include <asm/setup.h>
#include <asm/amigahw.h>
#include <asm/pgtable.h>
#include <linux/zorro.h>
#define Z2MINOR_COMBINED (0)
#define Z2MINOR_Z2ONLY (1)
#define Z2MINOR_CHIPONLY (2)
#define Z2MINOR_MEMLIST1 (4)
#define Z2MINOR_MEMLIST2 (5)
#define Z2MINOR_MEMLIST3 (6)
#define Z2MINOR_MEMLIST4 (7)
#define Z2MINOR_COUNT (8) /* Move this down when adding a new minor */
#define Z2RAM_CHUNK1024 ( Z2RAM_CHUNKSIZE >> 10 )
static DEFINE_MUTEX(z2ram_mutex);
static u_long *z2ram_map = NULL;
static u_long z2ram_size = 0;
static int z2_count = 0;
static int chip_count = 0;
static int list_count = 0;
static int current_device = -1;
static DEFINE_SPINLOCK(z2ram_lock);
static struct gendisk *z2ram_gendisk;
static struct request_queue *z2_queue;
static struct blk_mq_tag_set tag_set;
static const struct blk_mq_ops z2_mq_ops = {
.queue_rq = z2_queue_rq,
};
二、块设备操作集
在drivers.block/z2ram.c文件中定义了块设备的操作：
static const struct block_device_operations z2_fops =
{
.owner = THIS_MODULE,
.open = z2_open,
.release = z2_release,
};
即打开块设备的的时候回调z2_open函数，关闭块设备的时候回调z2_release函数。
2.1 z2_open
static int z2_open(struct block_device *bdev, fmode_t mode)
{
int device;
int max_z2_map = ( Z2RAM_SIZE / Z2RAM_CHUNKSIZE ) *
sizeof( z2ram_map[0] );
int max_chip_map = ( amiga_chip_size / Z2RAM_CHUNKSIZE ) *
sizeof( z2ram_map[0] );
int rc = -ENOMEM;
device = MINOR(bdev->bd_dev);
mutex_lock(&z2ram_mutex);
if ( current_device != -1 && current_device != device )
{
rc = -EBUSY;
goto err_out;
}
if ( current_device == -1 )
{
z2_count = 0;
chip_count = 0;
list_count = 0;
z2ram_size = 0;
/* Use a specific list entry. */
if (device >= Z2MINOR_MEMLIST1 && device <= Z2MINOR_MEMLIST4) {
int index = device - Z2MINOR_MEMLIST1 + 1;
unsigned long size, paddr, vaddr;
if (index >= m68k_realnum_memory) {
printk( KERN_ERR DEVICE_NAME
": no such entry in z2ram_map\n" );
goto err_out;
}
paddr = m68k_memory[index].addr;
size = m68k_memory[index].size & ~(Z2RAM_CHUNKSIZE-1);
#ifdef __powerpc__
/* FIXME: ioremap doesn't build correct memory tables. */
{
vfree(vmalloc (size));
}
vaddr = (unsigned long)ioremap_wt(paddr, size);
#else
vaddr = (unsigned long)z_remap_nocache_nonser(paddr, size);
#endif
z2ram_map =
kmalloc_array(size / Z2RAM_CHUNKSIZE,
sizeof(z2ram_map[0]),
GFP_KERNEL);
if ( z2ram_map == NULL )
{
printk( KERN_ERR DEVICE_NAME
": cannot get mem for z2ram_map\n" );
goto err_out;
}
while (size) {
z2ram_map[ z2ram_size++ ] = vaddr;
size -= Z2RAM_CHUNKSIZE;
vaddr += Z2RAM_CHUNKSIZE;
list_count++;
}
if ( z2ram_size != 0 )
printk( KERN_INFO DEVICE_NAME
": using %iK List Entry %d Memory\n",
list_count * Z2RAM_CHUNK1024, index );
} else
switch ( device )
{
case Z2MINOR_COMBINED:
z2ram_map = kmalloc( max_z2_map + max_chip_map, GFP_KERNEL );
if ( z2ram_map == NULL )
{
printk( KERN_ERR DEVICE_NAME
": cannot get mem for z2ram_map\n" );
goto err_out;
}
get_z2ram();
get_chipram();
if ( z2ram_size != 0 )
printk( KERN_INFO DEVICE_NAME
": using %iK Zorro II RAM and %iK Chip RAM (Total %dK)\n",
z2_count * Z2RAM_CHUNK1024,
chip_count * Z2RAM_CHUNK1024,
( z2_count + chip_count ) * Z2RAM_CHUNK1024 );
break;
case Z2MINOR_Z2ONLY:
z2ram_map = kmalloc( max_z2_map, GFP_KERNEL );
if ( z2ram_map == NULL )
{
printk( KERN_ERR DEVICE_NAME
": cannot get mem for z2ram_map\n" );
goto err_out;
}
get_z2ram();
if ( z2ram_size != 0 )
printk( KERN_INFO DEVICE_NAME
": using %iK of Zorro II RAM\n",
z2_count * Z2RAM_CHUNK1024 );
break;
case Z2MINOR_CHIPONLY:
z2ram_map = kmalloc( max_chip_map, GFP_KERNEL );
if ( z2ram_map == NULL )
{
printk( KERN_ERR DEVICE_NAME
": cannot get mem for z2ram_map\n" );
goto err_out;
}
get_chipram();
if ( z2ram_size != 0 )
printk( KERN_INFO DEVICE_NAME
": using %iK Chip RAM\n",
chip_count * Z2RAM_CHUNK1024 );
break;
default:
rc = -ENODEV;
goto err_out;
break;
}
if ( z2ram_size == 0 )
{
printk( KERN_NOTICE DEVICE_NAME
": no unused ZII/Chip RAM found\n" );
goto err_out_kfree;
}
current_device = device;
z2ram_size <<= Z2RAM_CHUNKSHIFT;
set_capacity(z2ram_gendisk, z2ram_size >> 9);
}
mutex_unlock(&z2ram_mutex);
return 0;
err_out_kfree:
kfree(z2ram_map);
err_out:
mutex_unlock(&z2ram_mutex);
return rc;
}
2.1.1 get_z2ram
static void
get_z2ram( void )
{
int i;
for ( i = 0; i < Z2RAM_SIZE / Z2RAM_CHUNKSIZE; i++ )
{
if ( test_bit( i, zorro_unused_z2ram ) )
{
z2_count++;
z2ram_map[z2ram_size++] = (unsigned long)ZTWO_VADDR(Z2RAM_START) +
(i << Z2RAM_CHUNKSHIFT);
clear_bit( i, zorro_unused_z2ram );
}
}
return;
}
2.1.2 get_chipram
static void
get_chipram( void )
{
while ( amiga_chip_avail() > ( Z2RAM_CHUNKSIZE * 4 ) )
{
chip_count++;
z2ram_map[ z2ram_size ] =
(u_long)amiga_chip_alloc( Z2RAM_CHUNKSIZE, "z2ram" );
if ( z2ram_map[ z2ram_size ] == 0 )
{
break;
}
z2ram_size++;
}
return;
}
2.2 z2_release
static void
z2_release(struct gendisk *disk, fmode_t mode)
{
mutex_lock(&z2ram_mutex);
if ( current_device == -1 ) {
mutex_unlock(&z2ram_mutex);
return;
}
mutex_unlock(&z2ram_mutex);
/*
* FIXME: unmap memory
*/
}
三、模块入口函数
module_init(z2_init);
我们定位到模块入口函数z2_init：
static int __init
z2_init(void)
{
int ret;
if (!MACH_IS_AMIGA)
return -ENODEV;
ret = -EBUSY;
if (register_blkdev(Z2RAM_MAJOR, DEVICE_NAME))
goto err;
ret = -ENOMEM;
z2ram_gendisk = alloc_disk(1);
if (!z2ram_gendisk)
goto out_disk;
z2_queue = blk_mq_init_sq_queue(&tag_set, &z2_mq_ops, 16,
BLK_MQ_F_SHOULD_MERGE);
if (IS_ERR(z2_queue)) {
ret = PTR_ERR(z2_queue);
z2_queue = NULL;
goto out_queue;
}
z2ram_gendisk->major = Z2RAM_MAJOR;
z2ram_gendisk->first_minor = 0;
z2ram_gendisk->fops = &z2_fops;
sprintf(z2ram_gendisk->disk_name, "z2ram");
z2ram_gendisk->queue = z2_queue;
add_disk(z2ram_gendisk);
blk_register_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT, THIS_MODULE,
z2_find, NULL, NULL);
return 0;
out_queue:
put_disk(z2ram_gendisk);
out_disk:
unregister_blkdev(Z2RAM_MAJOR, DEVICE_NAME);
err:
return ret;
}
在模块的入口函数中，主要执行了如下操作：
- 调用register_blkdev注册块设备主设备号，这里主设备号定义为Z2RAM_MAJOR=37，块设备名称为DEVICE_NAME="Z2RAM"；
- 使用alloc_disk申请一个通用磁盘对象gendisk，并且创建1个分区（除了代表磁盘的0号分区外）；
- 使用blk_mq_init_sq_queue初始化一个请求队列；
- 设置gendisk结构体的成员：
- 设置成员参数major、first_minor、disk_name、fops；
- 设置请求队列queue，等于之前初始化的请求队列；
- 使用add_disk注册gendisk；
- 使用blk_register_region建立磁盘设备号和gendisk的映射关系（这一步是不是多余的）；
3.1 z2_find
static struct kobject *z2_find(dev_t dev, int *part, void *data)
{
*part = 0;
return get_disk_and_module(z2ram_gendisk);
}
3.2 z2_mq_ops
z2_mq_ops为为块设备驱动行为的回调函数，z2_mq_ops定义为：
static const struct blk_mq_ops z2_mq_ops = {
.queue_rq = z2_queue_rq,
};
一旦I/O请求就绪，并且I/O调度器不想再把请求保持在队列上来排序或扩展，I/O调度器就会调用queue_rq函数。
z2_queue_rq函数定义为：
static blk_status_t z2_queue_rq(struct blk_mq_hw_ctx *hctx,
const struct blk_mq_queue_data *bd)
{
struct request *req = bd->rq;
unsigned long start = blk_rq_pos(req) << 9;
unsigned long len = blk_rq_cur_bytes(req);
blk_mq_start_request(req);
if (start + len > z2ram_size) {
pr_err(DEVICE_NAME ": bad access: block=%llu, "
"count=%u\n",
(unsigned long long)blk_rq_pos(req),
blk_rq_cur_sectors(req));
return BLK_STS_IOERR;
}
spin_lock_irq(&z2ram_lock);
while (len) {
unsigned long addr = start & Z2RAM_CHUNKMASK;
unsigned long size = Z2RAM_CHUNKSIZE - addr;
void *buffer = bio_data(req->bio);
if (len < size)
size = len;
addr += z2ram_map[ start >> Z2RAM_CHUNKSHIFT ];
if (rq_data_dir(req) == READ)
memcpy(buffer, (char *)addr, size);
else
memcpy((char *)addr, buffer, size);
start += size;
len -= size;
}
spin_unlock_irq(&z2ram_lock);
blk_mq_end_request(req, BLK_STS_OK);
return BLK_STS_OK;
}
四、模块出口函数
module_exit(z2_exit);
我们定位到模块入口函数z2_exit：
static void __exit z2_exit(void)
{
int i, j;
blk_unregister_region(MKDEV(Z2RAM_MAJOR, 0), Z2MINOR_COUNT);
unregister_blkdev(Z2RAM_MAJOR, DEVICE_NAME);
del_gendisk(z2ram_gendisk);
put_disk(z2ram_gendisk);
blk_cleanup_queue(z2_queue);
blk_mq_free_tag_set(&tag_set);
if ( current_device != -1 )
{
i = 0;
for ( j = 0 ; j < z2_count; j++ )
{
set_bit( i++, zorro_unused_z2ram );
}
for ( j = 0 ; j < chip_count; j++ )
{
if ( z2ram_map[ i ] )
{
amiga_chip_free( (void *) z2ram_map[ i++ ] );
}
}
if ( z2ram_map != NULL )
{
kfree( z2ram_map );
}
}
return;
}
在模块的出口函数中，主要执行了如下操作：
- 调用blk_unregister_region取消磁盘设备号和gendisk的映射关系（这一步是不是多余的）；
- 调用unregister_blkdev取消块设备主设备号注册；
- 调用del__gendisk释放磁盘gendisk；
- 调用put_disk注销磁盘gendisk；
- 调用blk_cleanup_queue清除内核中的请求队列request_queue；
- 调用blk_mq_free_tag_set释放 blk_mq_alloc_tag_set申请的标签集tag_set；
参考文章
标签：map,Z2RAM,queue,z2ram,linux,驱动,z2,size From： https://www.cnblogs.com/zyly/p/16704365.html