Linux-2.6平台下SCSI子系统之添加适配器到系统

SCSI低层驱动是面向主机适配器的，低层驱动被加载时，首先要添加主机适配器。主机适配器可以在PCI子系统完成ID匹配时添加，或者通过手动添加。所有基于硬件PCI接口的主机适配器都采用前一种方式，而UNH iSCSI启动器采用的是后一种方式。

添加主机适配器包括两部分内容：为主机适配器分配数据结构，将主机适配器添加到系统。

SCSI中间层为此提供了两个公共函数：scsi_host_alloc和scsi_add_host。

/**
 * scsi_host_alloc - register a scsi host adapter instance.
 * @sht: pointer to scsi host template
 * @privsize: extra bytes to allocate for driver
 *
 * Note:
 *  Allocate a new Scsi_Host and perform basic initialization.
 *  The host is not published to the scsi midlayer until scsi_add_host
 *  is called.
 *
 * Return value:
 *  Pointer to a new Scsi_Host
 **/

 

struct Scsi_Host *scsi_host_alloc(struct scsi_host_template *sht, int privsize)
{
 struct Scsi_Host *shost;
 gfp_t gfp_mask = GFP_KERNEL;
 int rval;

 if (sht->unchecked_isa_dma && privsize)
  gfp_mask |= __GFP_DMA;       //RAM的低16M作为DMA地址空间

 shost = kzalloc(sizeof(struct Scsi_Host) + privsize, gfp_mask);     //SCSI_Host的空间一次性分配，包括公有部分和私有部分。
 if (!shost)
  return NULL;

 shost->host_lock = &shost->default_lock;
 spin_lock_init(shost->host_lock);
 shost->shost_state = SHOST_CREATED;
 INIT_LIST_HEAD(&shost->__devices);
 INIT_LIST_HEAD(&shost->__targets);
 INIT_LIST_HEAD(&shost->eh_cmd_q);
 INIT_LIST_HEAD(&shost->starved_list);
 init_waitqueue_head(&shost->host_wait);

 mutex_init(&shost->scan_mutex);

 /*
  * subtract one because we increment first then return, but we need to
  * know what the next host number was before increment
  */
 shost->host_no = atomic_inc_return(&scsi_host_next_hn) - 1;       //host_no主机适配器编号，scsi_host_next_hn表示下一个新的主机适配器的编号。它的初始值为0，每次发现一个新的主机适配器，将全局变量scsi_host_next_hn的值赋给host_no域，然后再递增。
 shost->dma_channel = 0xff;

 /* These three are default values which can be overridden */
 shost->max_channel = 0;
 shost->max_id = 8;
 shost->max_lun = 8;

 /* Give each shost a default transportt */
 shost->transportt = &blank_transport_template;

 /*
  * All drivers right now should be able to handle 12 byte
  * commands.  Every so often there are requests for 16 byte
  * commands, but individual low-level drivers need to certify that
  * they actually do something sensible with such commands.
  */
 shost->max_cmd_len = 12;
 shost->hostt = sht;
 shost->this_id = sht->this_id;
 shost->can_queue = sht->can_queue;
 shost->sg_tablesize = sht->sg_tablesize;
 shost->cmd_per_lun = sht->cmd_per_lun;
 shost->unchecked_isa_dma = sht->unchecked_isa_dma;
 shost->use_clustering = sht->use_clustering;
 shost->ordered_tag = sht->ordered_tag;

 if (sht->supported_mode == MODE_UNKNOWN)
  /* means we didn't set it ... default to INITIATOR */
  shost->active_mode = MODE_INITIATOR;
 else
  shost->active_mode = sht->supported_mode;

 if (sht->max_host_blocked)
  shost->max_host_blocked = sht->max_host_blocked;
 else
  shost->max_host_blocked = SCSI_DEFAULT_HOST_BLOCKED;

 /*
  * If the driver imposes no hard sector transfer limit, start at
  * machine infinity initially.
  */
 if (sht->max_sectors)
  shost->max_sectors = sht->max_sectors;
 else
  shost->max_sectors = SCSI_DEFAULT_MAX_SECTORS;

 /*
  * assume a 4GB boundary, if not set
  */
 if (sht->dma_boundary)
  shost->dma_boundary = sht->dma_boundary;
 else
  shost->dma_boundary = 0xffffffff;

 device_initialize(&shost->shost_gendev);    //shost_gendev域内嵌通用设备，初始化；是内嵌类设备的辅设备。

 dev_set_name(&shost->shost_gendev, "host%d", shost->host_no);
#ifndef CONFIG_SYSFS_DEPRECATED
 shost->shost_gendev.bus = &scsi_bus_type;
#endif
 shost->shost_gendev.type = &scsi_host_type;

 device_initialize(&shost->shost_dev);            //shost_dev域是内嵌类设备，初始化该类设备，
 shost->shost_dev.parent = &shost->shost_gendev;
 shost->shost_dev.class = &shost_class;
 dev_set_name(&shost->shost_dev, "host%d", shost->host_no);
 shost->shost_dev.groups = scsi_sysfs_shost_attr_groups;

 shost->ehandler = kthread_run(scsi_error_handler, shost,       //SCSI错误恢复
   "scsi_eh_%d", shost->host_no);
 if (IS_ERR(shost->ehandler)) {
  rval = PTR_ERR(shost->ehandler);
  goto fail_kfree;
 }

 scsi_proc_hostdir_add(shost->hostt);     //在proc文件系统中为这个主机适配器添加一个目录
 return shost;

 fail_kfree:
 kfree(shost);
 return NULL;
}

在scsi_host_alloc函数被调用后，主机适配器还不会被公开给SCSI中间层，直到scsi_add_host函数被调用。

static inline int __must_check scsi_add_host(struct Scsi_Host *host,
          struct device *dev)
{
 return scsi_add_host_with_dma(host, dev, dev);
}

int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,             //第一个为指向主机适配器描述符的指针，第二个指向这个SCSI主机适配器驱动模型中的父设备的device描述符
      struct device *dma_dev)
{
 struct scsi_host_template *sht = shost->hostt;
 int error = -EINVAL;

 printk(KERN_INFO "scsi%d : %s\n", shost->host_no,
   sht->info ? sht->info(shost) : sht->name);

 if (!shost->can_queue) {                 //can_queue为主机适配器可以同时接受的命令数
  printk(KERN_ERR "%s: can_queue = 0 no longer supported\n",
    sht->name);
  goto fail;
 }

 error = scsi_setup_command_freelist(shost);
 if (error)
  goto fail;

 if (!shost->shost_gendev.parent)                     //确定主机适配器在sysfs中的位置
  shost->shost_gendev.parent = dev ? dev : &platform_bus;
 shost->dma_dev = dma_dev;

 error = device_add(&shost->shost_gendev);
 if (error)
  goto out;

 scsi_host_set_state(shost, SHOST_RUNNING);
 get_device(shost->shost_gendev.parent);

 error = device_add(&shost->shost_dev);
 if (error)
  goto out_del_gendev;

 get_device(&shost->shost_gendev);

 if (shost->transportt->host_size) {
  shost->shost_data = kzalloc(shost->transportt->host_size,
      GFP_KERNEL);
  if (shost->shost_data == NULL) {
   error = -ENOMEM;
   goto out_del_dev;
  }
 }

 if (shost->transportt->create_work_queue) {
  snprintf(shost->work_q_name, sizeof(shost->work_q_name),
    "scsi_wq_%d", shost->host_no);
  shost->work_q = create_singlethread_workqueue(
     shost->work_q_name);
  if (!shost->work_q) {
   error = -EINVAL;
   goto out_free_shost_data;
  }
 }

 error = scsi_sysfs_add_host(shost);
 if (error)
  goto out_destroy_host;

 scsi_proc_host_add(shost);
 return error;

 out_destroy_host:
 if (shost->work_q)
  destroy_workqueue(shost->work_q);
 out_free_shost_data:
 kfree(shost->shost_data);
 out_del_dev:
 device_del(&shost->shost_dev);
 out_del_gendev:
 device_del(&shost->shost_gendev);
 out:
 scsi_destroy_command_freelist(shost);
 fail:
 return error;
}

 

 

补充：

sysfs 是 Linux 内核中设计较新的一种虚拟的基于内存的文件系统，它的作用与 proc 有些类似，但除了与 proc 相同的具有查看和设定内核参数功能之外，还有为 Linux 统一设备模型作为管理之用。相比于 proc 文件系统，使用 sysfs 导出内核数据的方式更为统一，并且组织的方式更好，它的设计从 proc 中吸取了很多教训。本文就 sysfs 的挂载点 /sys 目录结构、其与 Linux 统一设备模型的关系、常见属性文件的用法等方面对 sysfs 作入门介绍，并且就内核编程方面，以具体的例子来展示如何添加 sysfs 支持。