init

源码基于5.10

default_bdi_init

static int __init default_bdi_init(void)
{int err;// 分配wq实例bdi_wq = alloc_workqueue("writeback", WQ_MEM_RECLAIM | WQ_UNBOUND |WQ_SYSFS, 0);if (!bdi_wq)return -ENOMEM;//　初始化noop_backing_dev_info，这个bdi没什么实际意义，一般在文件系统卸载了用err = bdi_init(&noop_backing_dev_info);return err;
}

bdi_alloc

struct backing_dev_info *bdi_alloc(int node_id)
{struct backing_dev_info *bdi;// 分配bdibdi = kzalloc_node(sizeof(*bdi), GFP_KERNEL, node_id);if (!bdi)return NULL;if (bdi_init(bdi)) {kfree(bdi);return NULL;}// 有回写能力bdi->capabilities = BDI_CAP_WRITEBACK | BDI_CAP_WRITEBACK_ACCT;// 最大预读的页数，VM_READAHEAD_PAGES＝128k/page_size=128k/4k=32页bdi->ra_pages = VM_READAHEAD_PAGES;// 最大的io页数bdi->io_pages = VM_READAHEAD_PAGES;return bdi;
}

bdi_init

static int bdi_init(struct backing_dev_info *bdi)
{int ret;bdi->dev = NULL;// 各种初始化kref_init(&bdi->refcnt);bdi->min_ratio = 0;bdi->max_ratio = 100;// FPROP_FRAC_BASE=1<<10bdi->max_prop_frac = FPROP_FRAC_BASE;INIT_LIST_HEAD(&bdi->bdi_list);INIT_LIST_HEAD(&bdi->wb_list);init_waitqueue_head(&bdi->wb_waitq);// 初始化cgroup相关ret = cgwb_bdi_init(bdi);return ret;
}static int cgwb_bdi_init(struct backing_dev_info *bdi)
{int ret;// 各种初始化INIT_RADIX_TREE(&bdi->cgwb_tree, GFP_ATOMIC);mutex_init(&bdi->cgwb_release_mutex);init_rwsem(&bdi->wb_switch_rwsem);// 终于到了初始化回写结构ret = wb_init(&bdi->wb, bdi, GFP_KERNEL);if (!ret) {// 初始化成功。设置mem, blk cgbdi->wb.memcg_css = &root_mem_cgroup->css;bdi->wb.blkcg_css = blkcg_root_css;}return ret;
}static int wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi,gfp_t gfp)
{int i, err;// 置0后，再各种初始化memset(wb, 0, sizeof(*wb));if (wb != &bdi->wb)bdi_get(bdi);wb->bdi = bdi;// 刷新时间戳wb->last_old_flush = jiffies;INIT_LIST_HEAD(&wb->b_dirty);INIT_LIST_HEAD(&wb->b_io);INIT_LIST_HEAD(&wb->b_more_io);INIT_LIST_HEAD(&wb->b_dirty_time);spin_lock_init(&wb->list_lock);// 带宽时间戳wb->bw_time_stamp = jiffies;// INIT_BW = (100 << (20 - PAGE_SHIFT))wb->balanced_dirty_ratelimit = INIT_BW;wb->dirty_ratelimit = INIT_BW;wb->write_bandwidth = INIT_BW;wb->avg_write_bandwidth = INIT_BW;spin_lock_init(&wb->work_lock);INIT_LIST_HEAD(&wb->work_list);// 回写工作队列，每次有任务的时候都会调用wb_workfnINIT_DELAYED_WORK(&wb->dwork, wb_workfn);wb->dirty_sleep = jiffies;// 完成回写的统计err = fprop_local_init_percpu(&wb->completions, gfp);if (err)goto out_put_bdi;// 初始化每个计数器，这是wb里统计的内存使用情况for (i = 0; i < NR_WB_STAT_ITEMS; i++) {err = percpu_counter_init(&wb->stat[i], 0, gfp);if (err)goto out_destroy_stat;}return 0;out_destroy_stat:while (i--)percpu_counter_destroy(&wb->stat[i]);fprop_local_destroy_percpu(&wb->completions);
out_put_bdi:if (wb != &bdi->wb)bdi_put(bdi);return err;
}

bdi_register_va

int bdi_register_va(struct backing_dev_info *bdi, const char *fmt, va_list args)
{struct device *dev;struct rb_node *parent, **p;// 已经注册过了if (bdi->dev)	/* The driver needs to use separate queues per device */return 0;vsnprintf(bdi->dev_name, sizeof(bdi->dev_name), fmt, args);// 创建一个设备对象，并在sysfs里注册dev = device_create(bdi_class, NULL, MKDEV(0, 0), bdi, bdi->dev_name);if (IS_ERR(dev))return PTR_ERR(dev);// 把bdi->wb加到bdi->wb_list里cgwb_bdi_register(bdi);// 设置设备bdi->dev = dev;// 在debugfs里创建stats目录bdi_debug_register(bdi, dev_name(dev));// 设置已注册状态set_bit(WB_registered, &bdi->wb.state);spin_lock_bh(&bdi_lock);// idbdi->id = ++bdi_id_cursor;// 下面这3个是把它加到bdi_tree里p = bdi_lookup_rb_node(bdi->id, &parent);rb_link_node(&bdi->rb_node, parent, p);rb_insert_color(&bdi->rb_node, &bdi_tree);// 加到bdi_list里list_add_tail_rcu(&bdi->bdi_list, &bdi_list);spin_unlock_bh(&bdi_lock);trace_writeback_bdi_register(bdi);return 0;
}