磁盤槽位和盤符綁定方案

Linux下的SCSI設備都是按照設備的發現順序命名的，對於磁盤盤符名稱就是sda，sdb，sdc等等。存儲設備一般都配有很多塊磁盤，盤符名稱和槽位號沒有對應關係，當磁盤插入，拔出時對應的盤符可能會變化。這給使用和運維帶來很多不便。

對於SCSI磁盤可通過修改sd_mod模塊中的sd_probe（drivers/scsi/sd.c）來完成“磁盤槽位和盤符”的綁定。

/**
 *	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;  
        ......

}

具體負責給gendisk分配磁盤名稱的就是 sd_format_disk_name，而決定磁盤名稱的index這個參數。index通過ida_get_new（include/linux/idr.h）獲取。ida是基於idr（底層是radix tree）實現的id分配器。從ida分配的index會被賦值給scsi_disk（drivers/scsi/sd.h）中的index，這個域作爲SCSI磁盤的索引，系統內唯一，不僅確定了設備名而且確定了設備的主設備號和次設備號（關於scsi_disk->index如何確定設備號可參見sd_probe_async）。爲了完成槽位和盤符綁定我們需要一個磁盤槽位和index的對應關係，這個對應關係可以根據系統中的一些不變量，如磁盤控制器的SCSI host號（系統範圍內唯一編號，用於標識這個主機適配器）來確定。Linux系統中SATA磁盤控制器上的每個磁盤都會被映射到一個單獨的SCSI host，對於只使用SATA控制器的陣列而言，可以採用如下方式綁定磁盤槽位和盤符。

以下是筆者根據scsi host（針對某款特定主板）確定SATA磁盤盤符對應關係的Patch：

將sd_probe中ida_get_new替換爲ida_get_new_above，這樣每次分配的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);

轉載請註明出處：http://blog.csdn.net/lkkey80/article/details/50263083