磁盘槽位和盘符绑定方案

Linux下的SCSI设备都是按照设备的发现顺序命名的，对于磁盘盘符名称就是sda，sdb，sdc等等。存储设备一般都配有很多块磁盘，盘符名称和槽位号没有对应关系，当磁盘插入，拔出时对应的盘符可能会变化。这给使用和运维带来很多不便。

对于SCSI磁盘可通过修改sd_mod模块中的sd_probe（drivers/scsi/sd.c）来完成“磁盘槽位和盘符”的绑定。

/**
*	sd_probe - called during driver initialization and whenever a
*	new scsi device is attached to the system. It is called once
*	for each scsi device (not just disks) present.
*	@dev: pointer to device object
*
*	Returns 0 if successful (or not interested in this scsi device
*	(e.g. scanner)); 1 when there is an error.
*
*	Note: this function is invoked from the scsi mid-level.
*	This function sets up the mapping between a given
*	<host,channel,id,lun> (found in sdp) and new device name
*	(e.g. /dev/sda). More precisely it is the block device major
*	and minor number that is chosen here.
*
*	Assume sd_attach is not re-entrant (for time being)
*	Also think about sd_attach() and sd_remove() running coincidentally.
**/
static int sd_probe(struct device *dev)
{
struct scsi_device *sdp = to_scsi_device(dev);
struct scsi_disk *sdkp;
struct gendisk *gd;
u32 index;
int error;

error = -ENODEV;
if (sdp->type != TYPE_DISK && sdp->type != TYPE_MOD && sdp->type != TYPE_RBC)
goto out;

SCSI_LOG_HLQUEUE(3, sdev_printk(KERN_INFO, sdp,
"sd_attach\n"));

error = -ENOMEM;
sdkp = kzalloc(sizeof(*sdkp), GFP_KERNEL);
if (!sdkp)
goto out;

gd = alloc_disk(SD_MINORS);
if (!gd)
goto out_free;

do {
if (!ida_pre_get(&sd_index_ida, GFP_KERNEL))
goto out_put;

spin_lock(&sd_index_lock);
error = ida_get_new(&sd_index_ida, &index);
spin_unlock(&sd_index_lock);
} while (error == -EAGAIN);

if (error)
goto out_put;

if (index >= SD_MAX_DISKS) {
error = -ENODEV;
sdev_printk(KERN_WARNING, sdp, "SCSI disk (sd) name space exhausted.\n");
goto out_free_index;
}

error = sd_format_disk_name("sd", index, gd->disk_name, DISK_NAME_LEN);
if (error)
goto out_free_index;

sdkp->device = sdp;
      sdkp->driver = &sd_template;                                                                       
      sdkp->disk = gd;
      sdkp->index = index;                                                                               
      sdkp->openers = 0;
      sdkp->previous_state = 1;  
......

}

具体负责给gendisk分配磁盘名称的就是 sd_format_disk_name，而决定磁盘名称的index这个参数。index通过ida_get_new（include/linux/idr.h）获取。ida是基于idr（底层是radix tree）实现的id分配器。从ida分配的index会被赋值给scsi_disk（drivers/scsi/sd.h）中的index，这个域作为SCSI磁盘的索引，系统内唯一，不仅确定了设备名而且确定了设备的主设备号和次设备号（关于scsi_disk->index如何确定设备号可参见sd_probe_async）。为了完成槽位和盘符绑定我们需要一个磁盘槽位和index的对应关系，这个对应关系可以根据系统中的一些不变量，如磁盘控制器的SCSI
host号（系统范围内唯一编号，用于标识这个主机适配器）来确定。Linux系统中SATA磁盘控制器上的每个磁盘都会被映射到一个单独的SCSI host，对于只使用SATA控制器的阵列而言，可以采用如下方式绑定磁盘槽位和盘符。

以下是笔者根据scsi host（针对某款特定主板）确定SATA磁盘盘符对应关系的Patch：

将sd_probe中ida_get_new替换为ida_get_new_above，这样每次分配的index == host_no。

do {
if (!ida_pre_get(&sd_index_ida, GFP_KERNEL))
goto out_put;

host_no = sdp->host->host_no;
spin_lock(&sd_index_lock);
//error = ida_get_new(&sd_index_ida, &index);
error = ida_get_new_above(&sd_index_ida, host_no, &index);
spin_unlock(&sd_index_lock);
} while (error == -EAGAIN);

转载请注明出处：http://blog.csdn.net/lkkey80/article/details/50263083