linux内核部件分析(六)——设备驱动模型之device

linux的设备驱动模型,是建立在sysfs和kobject之上的,由总线、设备、驱动、类所组成的关系结构。从本节开始,我们将对linux这一设备驱动模型进行深入分析。
头文件是include/linux/device.h,实现在drivers/base目录中。本节要分析的,是其中的设备,主要在core.c中。

struct device { struct device*parent; struct device_private *p; struct kobject kobj; const char*init_name; /* initial name of the device */ struct device_type *type; struct semaphore sem; /* semaphore to synchronize calls to * its driver. */ struct bus_type *bus; /* type of bus device is on */ struct device_driver *driver; /* which driver has allocated this device */ void*platform_data; /* Platform specific data, device core doesn't touch it */ struct dev_pm_info power; #ifdef CONFIG_NUMA intnuma_node; /* NUMA node this device is close to */ #endif u64*dma_mask; /* dma mask (if dma'able device) */ u64coherent_dma_mask; /* Like dma_mask, but for alloc_coherent mappings as not all hardware supports 64 bit addresses for consistent allocations such descriptors. */ struct device_dma_parameters *dma_parms; struct list_head dma_pools; /* dma pools (if dma'ble) */ struct dma_coherent_mem *dma_mem; /* internal for coherent mem override */ /* arch specific additions */ struct dev_archdata archdata; dev_tdevt; /* dev_t, creates the sysfs "dev" */ spinlock_tdevres_lock; struct list_head devres_head; struct klist_node knode_class; struct class*class; const struct attribute_group **groups; /* optional groups */ void (*release)(struct device *dev); };

先来分析下struct device的结构变量。首先是指向父节点的指针parent,kobj是内嵌在device中的kobject,用于把它联系到sysfs中。bus是对设备所在总线的指针,driver是对设备所用驱动的指针。还有DMA需要的数据,表示设备号的devt,表示设备资源的devres_head和保护它的devres_lock。指向类的指针class,knode_class是被连入class链表时所用的klist节点。group是设备的属性集合。release应该是设备释放时调用的函数。
struct device_private { struct klist klist_children; struct klist_node knode_parent; struct klist_node knode_driver; struct klist_node knode_bus; void *driver_data; struct device *device; }; #define to_device_private_parent(obj) \ container_of(obj, struct device_private, knode_parent) #define to_device_private_driver(obj) \ container_of(obj, struct device_private, knode_driver) #define to_device_private_bus(obj) \ container_of(obj, struct device_private, knode_bus)

struct device中有一部分不愿意让外界看到,所以做出struct device_private结构,包括了设备驱动模型内部的链接。klist_children是子设备的链表,knode_parent是连入父设备的klist_children时所用的节点,knode_driver是连入驱动的设备链表所用的节点,knode_bus是连入总线的设备链表时所用的节点。driver_data用于在设备结构中存放相关的驱动信息,也许是驱动专门为设备建立的结构实例。device则是指向struct device_private所属的device。
下面还有一些宏,to_device_private_parent()是从父设备的klist_children上节点,获得相应的device_private。to_device_private_driver()是从驱动的设备链表上节点,获得对应的device_private。to_device_private_bus()是从总线的设备链表上节点,获得对应的device_private。
或许会奇怪,为什么knode_class没有被移入struct device_private,或许有外部模块需要用到它。
/* * The type of device, "struct device" is embedded in. A class * or bus can contain devices of different types * like "partitions" and "disks", "mouse" and "event". * This identifies the device type and carries type-specific * information, equivalent to the kobj_type of a kobject. * If "name" is specified, the uevent will contain it in * the DEVTYPE variable. */ struct device_type { const char *name; const struct attribute_group **groups; int (*uevent)(struct device *dev, struct kobj_uevent_env *env); char *(*devnode)(struct device *dev, mode_t *mode); void (*release)(struct device *dev); const struct dev_pm_ops *pm; };

device竟然有device_type,类似于与kobject相对的kobj_type,之后我们再看它怎么用。
/* interface for exporting device attributes */ struct device_attribute { struct attribute attr; ssize_t (*show)(struct device *dev, struct device_attribute *attr, char *buf); ssize_t (*store)(struct device *dev, struct device_attribute *attr, const char *buf, size_t count); }; #define DEVICE_ATTR(_name, _mode, _show, _store) \ struct device_attribute dev_attr_##_name = __ATTR(_name, _mode, _show, _store)

这个device_attribute显然就是device对struct attribute的封装,新加的show()、store()函数都是以与设备相关的结构调用的。
至于device中其它的archdata、dma、devres,都是作为设备特有的,我们现在主要关心设备驱动模型的建立,这些会尽量忽略。

下面就来看看device的实现,这主要在core.c中。
int __init devices_init(void) { devices_kset = kset_create_and_add("devices", &device_uevent_ops, NULL); if (!devices_kset) return -ENOMEM; dev_kobj = kobject_create_and_add("dev", NULL); if (!dev_kobj) goto dev_kobj_err; sysfs_dev_block_kobj = kobject_create_and_add("block", dev_kobj); if (!sysfs_dev_block_kobj) goto block_kobj_err; sysfs_dev_char_kobj = kobject_create_and_add("char", dev_kobj); if (!sysfs_dev_char_kobj) goto char_kobj_err; return 0; char_kobj_err: kobject_put(sysfs_dev_block_kobj); block_kobj_err: kobject_put(dev_kobj); dev_kobj_err: kset_unregister(devices_kset); return -ENOMEM; }

这是在设备驱动模型初始化时调用的device部分初始的函数devices_init()。它干的事情我们都很熟悉,就是建立sysfs中的devices目录,和dev目录。还在dev目录下又建立了block和char两个子目录。因为dev目录只打算存放辅助的设备号,所以没必要使用kset。
static ssize_t dev_attr_show(struct kobject *kobj, struct attribute *attr, char *buf) { struct device_attribute *dev_attr = to_dev_attr(attr); struct device *dev = to_dev(kobj); ssize_t ret = -EIO; if (dev_attr->show) ret = dev_attr->show(dev, dev_attr, buf); if (ret >= (ssize_t)PAGE_SIZE) { print_symbol("dev_attr_show: %s returned bad count\n", (unsigned long)dev_attr->show); } return ret; }static ssize_t dev_attr_store(struct kobject *kobj, struct attribute *attr, const char *buf, size_t count) { struct device_attribute *dev_attr = to_dev_attr(attr); struct device *dev = to_dev(kobj); ssize_t ret = -EIO; if (dev_attr->store) ret = dev_attr->store(dev, dev_attr, buf, count); return ret; }static struct sysfs_ops dev_sysfs_ops = { .show = dev_attr_show, .store = dev_attr_store, };

看到这里是不是很熟悉,dev_sysfs_ops就是device准备注册到sysfs中的操作函数。dev_attr_show()和dev_attr_store()都会再调用与属性相关的函数。
static void device_release(struct kobject *kobj) { struct device *dev = to_dev(kobj); struct device_private *p = dev->p; if (dev->release) dev->release(dev); else if (dev->type && dev->type->release) dev->type->release(dev); else if (dev->class && dev->class->dev_release) dev->class->dev_release(dev); else WARN(1, KERN_ERR "Device '%s' does not have a release() " "function, it is broken and must be fixed.\n", dev_name(dev)); kfree(p); }static struct kobj_type device_ktype = { .release = device_release, .sysfs_ops = &dev_sysfs_ops, };

使用的release函数是device_release。在释放device时,会依次调用device结构中定义的release函数,device_type中定义的release函数,device所属的class中所定义的release函数,最后会吧device_private结构释放掉。

static int dev_uevent_filter(struct kset *kset, struct kobject *kobj) { struct kobj_type *ktype = get_ktype(kobj); if (ktype == &device_ktype) { struct device *dev = to_dev(kobj); if (dev->bus) return 1; if (dev->class) return 1; } return 0; }static const char *dev_uevent_name(struct kset *kset, struct kobject *kobj) { struct device *dev = to_dev(kobj); if (dev->bus) return dev->bus->name; if (dev->class) return dev->class->name; return NULL; }static int dev_uevent(struct kset *kset, struct kobject *kobj, struct kobj_uevent_env *env) { struct device *dev = to_dev(kobj); int retval = 0; /* add device node properties if present */ if (MAJOR(dev->devt)) { const char *tmp; const char *name; mode_t mode = 0; add_uevent_var(env, "MAJOR=%u", MAJOR(dev->devt)); add_uevent_var(env, "MINOR=%u", MINOR(dev->devt)); name = device_get_devnode(dev, &mode, &tmp); if (name) { add_uevent_var(env, "DEVNAME=%s", name); kfree(tmp); if (mode) add_uevent_var(env, "DEVMODE=%#o", mode & 0777); } } if (dev->type && dev->type->name) add_uevent_var(env, "DEVTYPE=%s", dev->type->name); if (dev->driver) add_uevent_var(env, "DRIVER=%s", dev->driver->name); #ifdef CONFIG_SYSFS_DEPRECATED if (dev->class) { struct device *parent = dev->parent; /* find first bus device in parent chain */ while (parent && !parent->bus) parent = parent->parent; if (parent && parent->bus) { const char *path; path = kobject_get_path(&parent->kobj, GFP_KERNEL); if (path) { add_uevent_var(env, "PHYSDEVPATH=%s", path); kfree(path); }add_uevent_var(env, "PHYSDEVBUS=%s", parent->bus->name); if (parent->driver) add_uevent_var(env, "PHYSDEVDRIVER=%s", parent->driver->name); } } else if (dev->bus) { add_uevent_var(env, "PHYSDEVBUS=%s", dev->bus->name); if (dev->driver) add_uevent_var(env, "PHYSDEVDRIVER=%s", dev->driver->name); } #endif /* have the bus specific function add its stuff */ if (dev->bus && dev->bus->uevent) { retval = dev->bus->uevent(dev, env); if (retval) pr_debug("device: '%s': %s: bus uevent() returned %d\n", dev_name(dev), __func__, retval); } /* have the class specific function add its stuff */ if (dev->class && dev->class->dev_uevent) { retval = dev->class->dev_uevent(dev, env); if (retval) pr_debug("device: '%s': %s: class uevent() " "returned %d\n", dev_name(dev), __func__, retval); } /* have the device type specific fuction add its stuff */ if (dev->type && dev->type->uevent) { retval = dev->type->uevent(dev, env); if (retval) pr_debug("device: '%s': %s: dev_type uevent() " "returned %d\n", dev_name(dev), __func__, retval); } return retval; }static struct kset_uevent_ops device_uevent_ops = { .filter = dev_uevent_filter, .name =dev_uevent_name, .uevent = dev_uevent, };

前面在讲到kset时,我们并未关注其中的kset_event_ops结构变量。但这里device既然用到了,我们就对其中的三个函数做简单介绍。kset_uevent_ops中的函数是用于管理kset内部kobject的uevent操作。其中filter函数用于阻止一个kobject向用户空间发送uevent,返回值为0表示阻止。这里dev_uevent_filter()检查device所属的bus或者class是否存在,如果都不存在,也就没有发送uevent的必要了。name函数是用于覆盖kset发送给用户空间的名称。这里dev_uevent_name()选择使用bus或者class的名称。uevent()函数是在uevent将被发送到用户空间之前调用的,用于向uevent中增加新的环境变量。dev_uevent()的实现很热闹,向uevent中添加了各种环境变量。
static ssize_t show_uevent(struct device *dev, struct device_attribute *attr, char *buf) { struct kobject *top_kobj; struct kset *kset; struct kobj_uevent_env *env = NULL; int i; size_t count = 0; int retval; /* search the kset, the device belongs to */ top_kobj = &dev->kobj; while (!top_kobj->kset && top_kobj->parent) top_kobj = top_kobj->parent; if (!top_kobj->kset) goto out; kset = top_kobj->kset; if (!kset->uevent_ops || !kset->uevent_ops->uevent) goto out; /* respect filter */ if (kset->uevent_ops && kset->uevent_ops->filter) if (!kset->uevent_ops->filter(kset, &dev->kobj)) goto out; env = kzalloc(sizeof(struct kobj_uevent_env), GFP_KERNEL); if (!env) return -ENOMEM; /* let the kset specific function add its keys */ retval = kset->uevent_ops->uevent(kset, &dev->kobj, env); if (retval) goto out; /* copy keys to file */ for (i = 0; i < env->envp_idx; i++) count += sprintf(&buf[count], "%s\n", env->envp[i]); out: kfree(env); return count; }static ssize_t store_uevent(struct device *dev, struct device_attribute *attr, const char *buf, size_t count) { enum kobject_action action; if (kobject_action_type(buf, count, &action) == 0) { kobject_uevent(&dev->kobj, action); goto out; } dev_err(dev, "uevent: unsupported action-string; this will " "be ignored in a future kernel version\n"); kobject_uevent(&dev->kobj, KOBJ_ADD); out: return count; }static struct device_attribute uevent_attr = __ATTR(uevent, S_IRUGO | S_IWUSR, show_uevent, store_uevent);

device不仅在kset中添加了对uevent的管理,而且还把uevent信息做成设备的一个属性uevent。其中show_event()是显示uevent中环境变量的,store_uevent()是发送uevent的。
static int device_add_attributes(struct device *dev, struct device_attribute *attrs) { int error = 0; int i; if (attrs) { for (i = 0; attr_name(attrs[i]); i++) { error = device_create_file(dev, &attrs[i]); if (error) break; } if (error) while (--i >= 0) device_remove_file(dev, &attrs[i]); } return error; }static void device_remove_attributes(struct device *dev, struct device_attribute *attrs) { int i; if (attrs) for (i = 0; attr_name(attrs[i]); i++) device_remove_file(dev, &attrs[i]); }static int device_add_groups(struct device *dev, const struct attribute_group **groups) { int error = 0; int i; if (groups) { for (i = 0; groups[i]; i++) { error = sysfs_create_group(&dev->kobj, groups[i]); if (error) { while (--i >= 0) sysfs_remove_group(&dev->kobj, groups[i]); break; } } } return error; }static void device_remove_groups(struct device *dev, const struct attribute_group **groups) { int i; if (groups) for (i = 0; groups[i]; i++) sysfs_remove_group(&dev->kobj, groups[i]); }

以上四个内部函数是用来向device中添加或删除属性与属性集合的。
device_add_attributes、device_remove_attributes、device_add_groups、device_remove_groups,都是直接通过sysfs提供的API实现。
static int device_add_attrs(struct device *dev) { struct class *class = dev->class; struct device_type *type = dev->type; int error; if (class) { error = device_add_attributes(dev, class->dev_attrs); if (error) return error; } if (type) { error = device_add_groups(dev, type->groups); if (error) goto err_remove_class_attrs; } error = device_add_groups(dev, dev->groups); if (error) goto err_remove_type_groups; return 0; err_remove_type_groups: if (type) device_remove_groups(dev, type->groups); err_remove_class_attrs: if (class) device_remove_attributes(dev, class->dev_attrs); return error; }static void device_remove_attrs(struct device *dev) { struct class *class = dev->class; struct device_type *type = dev->type; device_remove_groups(dev, dev->groups); if (type) device_remove_groups(dev, type->groups); if (class) device_remove_attributes(dev, class->dev_attrs); }

device_add_attrs()实际负责device中的属性添加。也是几个部分的集合,包括class中的dev_attrs,device_type中的groups,还有device本身的groups。
device_remove_attrs()则负责对应的device属性删除工作。

#define print_dev_t(buffer, dev)\ sprintf((buffer), "%u:%u\n", MAJOR(dev), MINOR(dev))static ssize_t show_dev(struct device *dev, struct device_attribute *attr, char *buf) { return print_dev_t(buf, dev->devt); }static struct device_attribute devt_attr = __ATTR(dev, S_IRUGO, show_dev, NULL);

这里又定义了一个名为dev的属性,就是显示设备的设备号。
/** * device_create_file - create sysfs attribute file for device. * @dev: device. * @attr: device attribute descriptor. */ int device_create_file(struct device *dev, struct device_attribute *attr) { int error = 0; if (dev) error = sysfs_create_file(&dev->kobj, &attr->attr); return error; }/** * device_remove_file - remove sysfs attribute file. * @dev: device. * @attr: device attribute descriptor. */ void device_remove_file(struct device *dev, struct device_attribute *attr) { if (dev) sysfs_remove_file(&dev->kobj, &attr->attr); }/** * device_create_bin_file - create sysfs binary attribute file for device. * @dev: device. * @attr: device binary attribute descriptor. */ int device_create_bin_file(struct device *dev, struct bin_attribute *attr) { int error = -EINVAL; if (dev) error = sysfs_create_bin_file(&dev->kobj, attr); return error; }/** * device_remove_bin_file - remove sysfs binary attribute file * @dev: device. * @attr: device binary attribute descriptor. */ void device_remove_bin_file(struct device *dev, struct bin_attribute *attr) { if (dev) sysfs_remove_bin_file(&dev->kobj, attr); }int device_schedule_callback_owner(struct device *dev, void (*func)(struct device *), struct module *owner) { return sysfs_schedule_callback(&dev->kobj, (void (*)(void *)) func, dev, owner); }


这里的五个函数,也是对sysfs提供的API的简单封装。
device_create_file()和device_remove_file()提供直接的属性文件管理方法。
device_create_bin_file()和device_remove_bin_file()则是提供设备管理二进制文件的方法。
device_schedule_callback_owner()也是简单地将func加入工作队列。

static void klist_children_get(struct klist_node *n) { struct device_private *p = to_device_private_parent(n); struct device *dev = p->device; get_device(dev); }static void klist_children_put(struct klist_node *n) { struct device_private *p = to_device_private_parent(n); struct device *dev = p->device; put_device(dev); }

如果之前认真看过klist的实现,应该知道,klist_children_get()和klist_children_put()就是在设备挂入和删除父设备的klist_children链表时调用的函数。在父设备klist_children链表上的指针,相当于对device的一个引用计数。
struct device *get_device(struct device *dev) { return dev ? to_dev(kobject_get(&dev->kobj)) : NULL; }/** * put_device - decrement reference count. * @dev: device in question. */ void put_device(struct device *dev) { /* might_sleep(); */ if (dev) kobject_put(&dev->kobj); }

device中的引用计数,完全交给内嵌的kobject来做。如果引用计数降为零,自然是调用之前说到的包含甚广的device_release函数。
void device_initialize(struct device *dev) { dev->kobj.kset = devices_kset; kobject_init(&dev->kobj, &device_ktype); INIT_LIST_HEAD(&dev->dma_pools); init_MUTEX(&dev->sem); spin_lock_init(&dev->devres_lock); INIT_LIST_HEAD(&dev->devres_head); device_init_wakeup(dev, 0); device_pm_init(dev); set_dev_node(dev, -1); }

device_initialize()就是device结构的初始化函数,它把device中能初始化的部分全初始化。它的界限在其中kobj的位置与device在设备驱动模型中的位置,这些必须由外部设置。可以看到,调用kobject_init()时,object的kobj_type选择了device_ktype,其中主要是sysops的两个函数,还有device_release函数。
static struct kobject *virtual_device_parent(struct device *dev) { static struct kobject *virtual_dir = NULL; if (!virtual_dir) virtual_dir = kobject_create_and_add("virtual", &devices_kset->kobj); return virtual_dir; }static struct kobject *get_device_parent(struct device *dev, struct device *parent) { int retval; if (dev->class) { struct kobject *kobj = NULL; struct kobject *parent_kobj; struct kobject *k; /* * If we have no parent, we live in "virtual". * Class-devices with a non class-device as parent, live * in a "glue" directory to prevent namespace collisions. */ if (parent == NULL) parent_kobj = virtual_device_parent(dev); else if (parent->class) return &parent->kobj; else parent_kobj = &parent->kobj; /* find our class-directory at the parent and reference it */ spin_lock(&dev->class->p->class_dirs.list_lock); list_for_each_entry(k, &dev->class->p->class_dirs.list, entry) if (k->parent == parent_kobj) { kobj = kobject_get(k); break; } spin_unlock(&dev->class->p->class_dirs.list_lock); if (kobj) return kobj; /* or create a new class-directory at the parent device */ k = kobject_create(); if (!k) return NULL; k->kset = &dev->class->p->class_dirs; retval = kobject_add(k, parent_kobj, "%s", dev->class->name); if (retval < 0) { kobject_put(k); return NULL; } /* do not emit an uevent for this simple "glue" directory */ return k; } if (parent) return &parent->kobj; return NULL; }

这里的get_device_parent()就是获取父节点的kobject,但也并非就如此简单。get_device_parent()的返回值直接决定了device将被挂在哪个目录下。到底该挂在哪,是由dev->class、dev->parent、dev->parent->class等因素综合决定的。我们看get_device_parent()中是如何判断的。如果dev->class为空,表示一切随父设备,有parent则返回parent->kobj,没有则返回NULL。如果有dev->class呢,情况就比较复杂了,也许device有着与parent不同的class,也许device还没有一个parent,等等。我们看具体的情况。如果parent不为空,而且存在parent->class,则还放在parent目录下。不然,要么parent不存在,要么parent没有class,很难直接将有class的device放在parent下面。目前的解决方法很简单,在parent与device之间,再加一层表示class的目录。如果parent都没有,那就把/sys/devices/virtual当做parent。class->p->class_dirs就是专门存放这种中间kobject的kset。思路理清后,再结合实际的sysfs,代码就很容易看懂了。
static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir) { /* see if we live in a "glue" directory */ if (!glue_dir || !dev->class || glue_dir->kset != &dev->class->p->class_dirs) return; kobject_put(glue_dir); }static void cleanup_device_parent(struct device *dev) { cleanup_glue_dir(dev, dev->kobj.parent); }

cleanup_device_parent()是取消对parent引用时调用的函数,看起来只针对这种glue形式的目录起作用。
static void setup_parent(struct device *dev, struct device *parent) { struct kobject *kobj; kobj = get_device_parent(dev, parent); if (kobj) dev->kobj.parent = kobj; }

setup_parent()就是调用get_device_parent()获得应该存放的父目录kobj,并把dev->kobj.parent设为它。
static int device_add_class_symlinks(struct device *dev) { int error; if (!dev->class) return 0; error = sysfs_create_link(&dev->kobj, &dev->class->p->class_subsys.kobj, "subsystem"); if (error) goto out; /* link in the class directory pointing to the device */ error = sysfs_create_link(&dev->class->p->class_subsys.kobj, &dev->kobj, dev_name(dev)); if (error) goto out_subsys; if (dev->parent && device_is_not_partition(dev)) { error = sysfs_create_link(&dev->kobj, &dev->parent->kobj, "device"); if (error) goto out_busid; } return 0; out_busid: sysfs_remove_link(&dev->class->p->class_subsys.kobj, dev_name(dev)); out_subsys: sysfs_remove_link(&dev->kobj, "subsystem"); out: return error; }

device_add_class_symlinks()在device和class直接添加一些软链接。在device目录下创建指向class的subsystem文件,在class目录下创建指向device的同名文件。如果device有父设备,而且device不是块设备分区,则在device目录下建立一个指向父设备的device链接文件。这一点在usb设备和usb接口间很常见。
static void device_remove_class_symlinks(struct device *dev) { if (!dev->class) return; #ifdef CONFIG_SYSFS_DEPRECATED if (dev->parent && device_is_not_partition(dev)) { char *class_name; class_name = make_class_name(dev->class->name, &dev->kobj); if (class_name) { sysfs_remove_link(&dev->parent->kobj, class_name); kfree(class_name); } sysfs_remove_link(&dev->kobj, "device"); } if (dev->kobj.parent != &dev->class->p->class_subsys.kobj && device_is_not_partition(dev)) sysfs_remove_link(&dev->class->p->class_subsys.kobj, dev_name(dev)); #else if (dev->parent && device_is_not_partition(dev)) sysfs_remove_link(&dev->kobj, "device"); sysfs_remove_link(&dev->class->p->class_subsys.kobj, dev_name(dev)); #endif sysfs_remove_link(&dev->kobj, "subsystem"); }

device_remove_class_symlinks()删除device和class之间的软链接。
static inline const char *dev_name(const struct device *dev) { return kobject_name(&dev->kobj); }int dev_set_name(struct device *dev, const char *fmt, ...) { va_list vargs; int err; va_start(vargs, fmt); err = kobject_set_name_vargs(&dev->kobj, fmt, vargs); va_end(vargs); return err; }

dev_name()获得设备名称,dev_set_name()设置设备名称。但这里的dev_set_name()只能在设备未注册前使用。device的名称其实是完全靠dev->kobj管理的。
static struct kobject *device_to_dev_kobj(struct device *dev) { struct kobject *kobj; if (dev->class) kobj = dev->class->dev_kobj; else kobj = sysfs_dev_char_kobj; return kobj; }

device_to_dev_kobj()为dev选择合适的/sys/dev下的kobject,或者是块设备,或者是字符设备,或者没有。
#define format_dev_t(buffer, dev)\ ({\ sprintf(buffer, "%u:%u", MAJOR(dev), MINOR(dev)); \ buffer; \ })static int device_create_sys_dev_entry(struct device *dev) { struct kobject *kobj = device_to_dev_kobj(dev); int error = 0; char devt_str[15]; if (kobj) { format_dev_t(devt_str, dev->devt); error = sysfs_create_link(kobj, &dev->kobj, devt_str); } return error; }static void device_remove_sys_dev_entry(struct device *dev) { struct kobject *kobj = device_to_dev_kobj(dev); char devt_str[15]; if (kobj) { format_dev_t(devt_str, dev->devt); sysfs_remove_link(kobj, devt_str); } }

device_create_sys_dev_entry()是在/sys/dev相应的目录下建立对设备的软链接。先是通过device_to_dev_kobj()获得父节点的kobj,然后调用sysfs_create_link()建立软链接。
device_remove_sys_dev_entry()与其操作正相反,删除在/sys/dev下建立的软链接。
int device_private_init(struct device *dev) { dev->p = kzalloc(sizeof(*dev->p), GFP_KERNEL); if (!dev->p) return -ENOMEM; dev->p->device = dev; klist_init(&dev->p->klist_children, klist_children_get, klist_children_put); return 0; }

device_private_init()分配并初始化dev->p。至于空间的释放,是等到释放设备时调用的device_release()中。

之前的函数比较散乱,或许找不出一个整体的印象。但下面马上就要看到重要的部分了,因为代码终于攒到了爆发的程度!
/** * device_register - register a device with the system. * @dev: pointer to the device structure * * This happens in two clean steps - initialize the device * and add it to the system. The two steps can be called * separately, but this is the easiest and most common. * I.e. you should only call the two helpers separately if * have a clearly defined need to use and refcount the device * before it is added to the hierarchy. * * NOTE: _Never_ directly free @dev after calling this function, even * if it returned an error! Always use put_device() to give up the * reference initialized in this function instead. */ int device_register(struct device *dev) { device_initialize(dev); return device_add(dev); }

device_register()是提供给外界注册设备的接口。它先是调用device_initialize()初始化dev结构,然后调用device_add()将其加入系统中。但要注意,在调用device_register()注册dev之前,有一些dev结构变量是需要自行设置的。这其中有指明设备位置的struct device *parent,struct bus_type *bus, struct class *class,有指明设备属性的 const char *init_name, struct device_type *type, const struct attribute_group **groups, void (*release)(struct device *dev), dev_t devt,等等。不同设备的使用方法不同,我们留待之后再具体分析。device_initialize()我们已经看过,下面重点看看device_add()是如何实现的。
int device_add(struct device *dev) { struct device *parent = NULL; struct class_interface *class_intf; int error = -EINVAL; dev = get_device(dev); if (!dev) goto done; if (!dev->p) { error = device_private_init(dev); if (error) goto done; } /* * for statically allocated devices, which should all be converted * some day, we need to initialize the name. We prevent reading back * the name, and force the use of dev_name() */ if (dev->init_name) { dev_set_name(dev, "%s", dev->init_name); dev->init_name = NULL; } if (!dev_name(dev)) goto name_error; pr_debug("device: '%s': %s\n", dev_name(dev), __func__); parent = get_device(dev->parent); setup_parent(dev, parent); /* use parent numa_node */ if (parent) set_dev_node(dev, dev_to_node(parent)); /* first, register with generic layer. */ /* we require the name to be set before, and pass NULL */ error = kobject_add(&dev->kobj, dev->kobj.parent, NULL); if (error) goto Error; /* notify platform of device entry */ if (platform_notify) platform_notify(dev); error = device_create_file(dev, &uevent_attr); if (error) goto attrError; if (MAJOR(dev->devt)) { error = device_create_file(dev, &devt_attr); if (error) goto ueventattrError; error = device_create_sys_dev_entry(dev); if (error) goto devtattrError; devtmpfs_create_node(dev); } error = device_add_class_symlinks(dev); if (error) goto SymlinkError; error = device_add_attrs(dev); if (error) goto AttrsError; error = bus_add_device(dev); if (error) goto BusError; error = dpm_sysfs_add(dev); if (error) goto DPMError; device_pm_add(dev); /* Notify clients of device addition.This call must come * after dpm_sysf_add() and before kobject_uevent(). */ if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, BUS_NOTIFY_ADD_DEVICE, dev); kobject_uevent(&dev->kobj, KOBJ_ADD); bus_probe_device(dev); if (parent) klist_add_tail(&dev->p->knode_parent, &parent->p->klist_children); if (dev->class) { mutex_lock(&dev->class->p->class_mutex); /* tie the class to the device */ klist_add_tail(&dev->knode_class, &dev->class->p->class_devices); /* notify any interfaces that the device is here */ list_for_each_entry(class_intf, &dev->class->p->class_interfaces, node) if (class_intf->add_dev) class_intf->add_dev(dev, class_intf); mutex_unlock(&dev->class->p->class_mutex); } done: put_device(dev); return error; DPMError: bus_remove_device(dev); BusError: device_remove_attrs(dev); AttrsError: device_remove_class_symlinks(dev); SymlinkError: if (MAJOR(dev->devt)) device_remove_sys_dev_entry(dev); devtattrError: if (MAJOR(dev->devt)) device_remove_file(dev, &devt_attr); ueventattrError: device_remove_file(dev, &uevent_attr); attrError: kobject_uevent(&dev->kobj, KOBJ_REMOVE); kobject_del(&dev->kobj); Error: cleanup_device_parent(dev); if (parent) put_device(parent); name_error: kfree(dev->p); dev->p = NULL; goto done; }

device_add()将dev加入设备驱动模型。它先是调用get_device(dev)增加dev的引用计数,然后调用device_private_init()分配和初始化dev->p,调用dev_set_name()设置dev名字。然后是准备将dev加入sysfs,先是用get_device(parent)增加对parent的引用计数(无论是直接挂在parent下还是通过一个类层挂在parent下都要增加parent的引用计数),然后调用setup_parent()找到实际要加入的父kobject,通过kobject_add()加入其下。然后是添加属性和属性集合的操作,调用device_create_file()添加uevent属性,调用device_add_attrs()添加device/type/class预定义的属性与属性集合。如果dev有被分配设备号,再用device_create_file()添加dev属性,并用device_create_sys_dev_entry()在/sys/dev下添加相应的软链接,最后调用devtmpfs_create_node()在/dev下创建相应的设备文件。然后调用device_add_class_symlinks()添加dev与class间的软链接,调用bus_add_device()添加dev与bus间的软链接,并将dev挂入bus的设备链表。调用dpm_sysfs_add()增加dev下的power属性集合,调用device_pm_add()将dev加入dpm_list链表。
调用kobject_uevent()发布KOBJ_ADD消息,调用bus_probe_device()为dev寻找合适的驱动。如果有parent节点,把dev->p->knode_parent挂入parent->p->klist_children链表。如果dev有所属的class,将dev->knode_class挂在class->p->class_devices上,并调用可能的类设备接口的add_dev()方法。可能对于直接在bus上的设备来说,自然可以调用bus_probe_device()查找驱动,而不与总线直接接触的设备,则要靠class来发现驱动,这里的class_interface中的add_dev()方法,就是一个绝好的机会。最后会调用put_device(dev)释放在函数开头增加的引用计数。
device_add()要做的事很多,但想想每件事都在情理之中。device是设备驱动模型的基本元素,在class、bus、dev、devices中都有它的身影。device_add()要适应各种类型的设备注册,自然会越来越复杂。可以说文件开头定义的内部函数,差不多都是为了这里服务的。

void device_unregister(struct device *dev) { pr_debug("device: '%s': %s\n", dev_name(dev), __func__); device_del(dev); put_device(dev); }

有注册自然又注销。device_unregister()就是用于将dev从系统中注销,并释放创建时产生的引用计数。
void device_del(struct device *dev) { struct device *parent = dev->parent; struct class_interface *class_intf; /* Notify clients of device removal.This call must come * before dpm_sysfs_remove(). */ if (dev->bus) blocking_notifier_call_chain(&dev->bus->p->bus_notifier, BUS_NOTIFY_DEL_DEVICE, dev); device_pm_remove(dev); dpm_sysfs_remove(dev); if (parent) klist_del(&dev->p->knode_parent); if (MAJOR(dev->devt)) { devtmpfs_delete_node(dev); device_remove_sys_dev_entry(dev); device_remove_file(dev, &devt_attr); } if (dev->class) { device_remove_class_symlinks(dev); mutex_lock(&dev->class->p->class_mutex); /* notify any interfaces that the device is now gone */ list_for_each_entry(class_intf, &dev->class->p->class_interfaces, node) if (class_intf->remove_dev) class_intf->remove_dev(dev, class_intf); /* remove the device from the class list */ klist_del(&dev->knode_class); mutex_unlock(&dev->class->p->class_mutex); } device_remove_file(dev, &uevent_attr); device_remove_attrs(dev); bus_remove_device(dev); /* * Some platform devices are driven without driver attached * and managed resources may have been acquired.Make sure * all resources are released. */ devres_release_all(dev); /* Notify the platform of the removal, in case they * need to do anything... */ if (platform_notify_remove) platform_notify_remove(dev); kobject_uevent(&dev->kobj, KOBJ_REMOVE); cleanup_device_parent(dev); kobject_del(&dev->kobj); put_device(parent); }

device_del()是与device_add()相对的函数,进行实际的将dev从系统中脱离的工作。这其中既有将dev从设备驱动模型各种链表中脱离的工作,又有将dev从sysfs的各个角落删除的工作。大致流程与dev_add()相对,就不一一介绍。
【linux内核部件分析(六)——设备驱动模型之device】
爆发结束,下面来看一些比较轻松的函数。
/** * device_get_devnode - path of device node file * @dev: device * @mode: returned file access mode * @tmp: possibly allocated string * * Return the relative path of a possible device node. * Non-default names may need to allocate a memory to compose * a name. This memory is returned in tmp and needs to be * freed by the caller. */ const char *device_get_devnode(struct device *dev, mode_t *mode, const char **tmp) { char *s; *tmp = NULL; /* the device type may provide a specific name */ if (dev->type && dev->type->devnode) *tmp = dev->type->devnode(dev, mode); if (*tmp) return *tmp; /* the class may provide a specific name */ if (dev->class && dev->class->devnode) *tmp = dev->class->devnode(dev, mode); if (*tmp) return *tmp; /* return name without allocation, tmp == NULL */ if (strchr(dev_name(dev), '!') == NULL) return dev_name(dev); /* replace '!' in the name with '/' */ *tmp = kstrdup(dev_name(dev), GFP_KERNEL); if (!*tmp) return NULL; while ((s = strchr(*tmp, '!'))) s[0] = '/'; return *tmp; }

device_get_devnode()返回设备的路径名。不过似乎可以由device_type或者class定义一些独特的返回名称。
static struct device *next_device(struct klist_iter *i) { struct klist_node *n = klist_next(i); struct device *dev = NULL; struct device_private *p; if (n) { p = to_device_private_parent(n); dev = p->device; } return dev; }int device_for_each_child(struct device *parent, void *data, int (*fn)(struct device *dev, void *data)) { struct klist_iter i; struct device *child; int error = 0; if (!parent->p) return 0; klist_iter_init(&parent->p->klist_children, &i); while ((child = next_device(&i)) && !error) error = fn(child, data); klist_iter_exit(&i); return error; }struct device *device_find_child(struct device *parent, void *data, int (*match)(struct device *dev, void *data)) { struct klist_iter i; struct device *child; if (!parent) return NULL; klist_iter_init(&parent->p->klist_children, &i); while ((child = next_device(&i))) if (match(child, data) && get_device(child)) break; klist_iter_exit(&i); return child; }

device_for_each_child()对dev下的每个子device,都调用一遍特定的处理函数。
device_find_child()则是查找dev下特点的子device,查找使用特定的match函数。
这两个遍历过程都使用了klist特有的遍历函数,支持遍历过程中的节点删除等功能。next_device()则是为了遍历方便封装的一个内部函数。

下面本该是root_device注册相关的代码。但经过检查,linux内核中使用到的root_device很少见,而且在sysfs中也未能找到一个实际的例子。所以root_device即使还未被弃用,也并非主流,我们将其跳过。
与kobject和kset类似,device也为我们提供了快速device创建方法,下面就看看吧。
static void device_create_release(struct device *dev) { pr_debug("device: '%s': %s\n", dev_name(dev), __func__); kfree(dev); }struct device *device_create_vargs(struct class *class, struct device *parent, dev_t devt, void *drvdata, const char *fmt, va_list args) { struct device *dev = NULL; int retval = -ENODEV; if (class == NULL || IS_ERR(class)) goto error; dev = kzalloc(sizeof(*dev), GFP_KERNEL); if (!dev) { retval = -ENOMEM; goto error; } dev->devt = devt; dev->class = class; dev->parent = parent; dev->release = device_create_release; dev_set_drvdata(dev, drvdata); retval = kobject_set_name_vargs(&dev->kobj, fmt, args); if (retval) goto error; retval = device_register(dev); if (retval) goto error; return dev; error: put_device(dev); return ERR_PTR(retval); }struct device *device_create(struct class *class, struct device *parent, dev_t devt, void *drvdata, const char *fmt, ...) { va_list vargs; struct device *dev; va_start(vargs, fmt); dev = device_create_vargs(class, parent, devt, drvdata, fmt, vargs); va_end(vargs); return dev; }

这里的device_create()提供了一个快速的dev创建注册方法。只是中间没有提供设置device_type的方法,或许是这样的device已经够特立独行了,不需要搞出一类来。

static int __match_devt(struct device *dev, void *data) { dev_t *devt = data; return dev->devt == *devt; }void device_destroy(struct class *class, dev_t devt) { struct device *dev; dev = class_find_device(class, NULL, &devt, __match_devt); if (dev) { put_device(dev); device_unregister(dev); } }

device_destroy()就是与device_create()相对的注销函数。至于这里为什么会多一个put_device(dev),也很简单,因为在class_find_device()找到dev时,调用了get_device()。
struct device *class_find_device(struct class *class, struct device *start, void *data, int (*match)(struct device *, void *)) { struct class_dev_iter iter; struct device *dev; if (!class) return NULL; if (!class->p) { WARN(1, "%s called for class '%s' before it was initialized", __func__, class->name); return NULL; } class_dev_iter_init(&iter, class, start, NULL); while ((dev = class_dev_iter_next(&iter))) { if (match(dev, data)) { get_device(dev); break; } } class_dev_iter_exit(&iter); return dev; }

class_find_device()本来是class.c中的内容,其实现也于之前将的遍历dev->p->klist_children类似,无非是在klist提供的遍历方法上加以封装。但我们这里列出class_find_device()的实现与使用它的device_destroy(),却是为了更好地分析这个调用流程中dev是如何被保护的。它实际上是经历了三个保护手段:首先在class_dev_iter_next()->klist_next()中,是受到struct klist中 spinlock_t k_lock保护的。在找到下一点并解锁之前,就增加了struct klist_node中的struct kref n_ref引用计数。在当前的next()调用完,到下一个next()调用之前,都是受这个增加的引用计数保护的。再看class_find_device()中,使用get_device(dev)增加了dev本身的引用计数保护(当然也要追溯到kobj->kref中),这是第三种保护。知道device_destroy()中主动调用put_device(dev)才去除了这种保护。
本来对dev的保护,应该完全是由dev中的引用计数完成的。但实际上这种保护很多时候是间接完成的。例如这里的klist中的自旋锁,klist_node中的引用计数,都不过是为了保持class的设备链表中对dev的引用计数不消失,这是一种间接保护的手段,保证了这中间即使外界主动释放class设备链表对dev的引用计数,dev仍然不会被实际注销。这种曲折的联系,才真正发挥了引用计数的作用,构成设备驱动模型独特的魅力。
int device_rename(struct device *dev, char *new_name) { char *old_device_name = NULL; int error; dev = get_device(dev); if (!dev) return -EINVAL; pr_debug("device: '%s': %s: renaming to '%s'\n", dev_name(dev), __func__, new_name); old_device_name = kstrdup(dev_name(dev), GFP_KERNEL); if (!old_device_name) { error = -ENOMEM; goto out; } error = kobject_rename(&dev->kobj, new_name); if (error) goto out; if (dev->class) { error = sysfs_create_link_nowarn(&dev->class->p->class_subsys.kobj, &dev->kobj, dev_name(dev)); if (error) goto out; sysfs_remove_link(&dev->class->p->class_subsys.kobj, old_device_name); } out: put_device(dev); kfree(old_device_name); return error; }

device_rename()是供设备注册后改变名称用的,除了改变/sys/devices下地名称,还改变了/sys/class下地软链接名称。前者很自然,但后者却很难想到。即使简单的地方,经过重重调试,我们也会惊讶于linux的心细如发。
static int device_move_class_links(struct device *dev, struct device *old_parent, struct device *new_parent) { int error = 0; if (old_parent) sysfs_remove_link(&dev->kobj, "device"); if (new_parent) error = sysfs_create_link(&dev->kobj, &new_parent->kobj, "device"); return error; #endif }

device_move_class_links()只是一个内部函数,后面还有操纵它的那只手。这里的device_move_class_links显得很名不副实,并没用操作class中软链接的举动。这很正常,因为在sysfs中软链接是针对kobject来说的,所以即使位置变掉了,软链接还是很很准确地定位。
/** * device_move - moves a device to a new parent * @dev: the pointer to the struct device to be moved * @new_parent: the new parent of the device (can by NULL) * @dpm_order: how to reorder the dpm_list */ int device_move(struct device *dev, struct device *new_parent, enum dpm_order dpm_order) { int error; struct device *old_parent; struct kobject *new_parent_kobj; dev = get_device(dev); if (!dev) return -EINVAL; device_pm_lock(); new_parent = get_device(new_parent); new_parent_kobj = get_device_parent(dev, new_parent); pr_debug("device: '%s': %s: moving to '%s'\n", dev_name(dev), __func__, new_parent ? dev_name(new_parent) : ""); error = kobject_move(&dev->kobj, new_parent_kobj); if (error) { cleanup_glue_dir(dev, new_parent_kobj); put_device(new_parent); goto out; } old_parent = dev->parent; dev->parent = new_parent; if (old_parent) klist_remove(&dev->p->knode_parent); if (new_parent) { klist_add_tail(&dev->p->knode_parent, &new_parent->p->klist_children); set_dev_node(dev, dev_to_node(new_parent)); } if (!dev->class) goto out_put; error = device_move_class_links(dev, old_parent, new_parent); if (error) { /* We ignore errors on cleanup since we're hosed anyway... */ device_move_class_links(dev, new_parent, old_parent); if (!kobject_move(&dev->kobj, &old_parent->kobj)) { if (new_parent) klist_remove(&dev->p->knode_parent); dev->parent = old_parent; if (old_parent) { klist_add_tail(&dev->p->knode_parent, &old_parent->p->klist_children); set_dev_node(dev, dev_to_node(old_parent)); } } cleanup_glue_dir(dev, new_parent_kobj); put_device(new_parent); goto out; } switch (dpm_order) { case DPM_ORDER_NONE: break; case DPM_ORDER_DEV_AFTER_PARENT: device_pm_move_after(dev, new_parent); break; case DPM_ORDER_PARENT_BEFORE_DEV: device_pm_move_before(new_parent, dev); break; case DPM_ORDER_DEV_LAST: device_pm_move_last(dev); break; } out_put: put_device(old_parent); out: device_pm_unlock(); put_device(dev); return error; }


device_move()就是将dev移到一个新的parent下。但也有可能这个parent是空的。大部分操作围绕在引用计数上,get_device(),put_device()。而且换了新的parent,到底要加到sysfs中哪个目录下,还要再调用get_device_parent()研究一下。主要的操作就是kobject_move()和device_move_class_links()。因为在sysfs中软链接是针对kobject来说的,所以即使位置变掉了,软链接还是很很准确地定位,所以在/sys/dev、/sys/bus、/sys/class中的软链接都不用变,这实在是sysfs的一大优势。除此之外,device_move()还涉及到电源管理的问题,device移动影响到dev在dpm_list上的位置,我们对此不了解,先忽略之。
void device_shutdown(void) { struct device *dev, *devn; list_for_each_entry_safe_reverse(dev, devn, &devices_kset->list, kobj.entry) { if (dev->bus && dev->bus->shutdown) { dev_dbg(dev, "shutdown\n"); dev->bus->shutdown(dev); } else if (dev->driver && dev->driver->shutdown) { dev_dbg(dev, "shutdown\n"); dev->driver->shutdown(dev); } } kobject_put(sysfs_dev_char_kobj); kobject_put(sysfs_dev_block_kobj); kobject_put(dev_kobj); async_synchronize_full(); }

这个device_shutdown()是在系统关闭时才调用的。它动用了很少使用的devices_kset,从而可以遍历到每个注册到sysfs上的设备,调用相应的总线或驱动定义的shutdown()函数。提起这个,还是在device_initialize()中将dev->kobj->kset统一设为devices_kset的。原来设备虽然有不同的parent,但kset还是一样的。这样我们就能理解/sys/devices下的顶层设备目录是怎么来的,因为没用parent,就在调用kobject_add()时将kset->kobj当成了parent,所以会直接挂在顶层目录下。这样的目录大致有pci0000:00、virtual等等。

看完了core.c,我有种明白机器人也是由零件组成的的感觉。linux设备驱动模型的大门已经打开了四分之一。随着分析的深入,我们大概也会越来越明白linux的良苦用心。





























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