/* main structure for soundcard */
struct snd_card {
int number; /* number of soundcard (index to
snd_cards) */
char id[16]; /* id string of this card */
char driver[16]; /* driver name */
char shortname[32]; /* short name of this soundcard */
char longname[80]; /* name of this soundcard */
char mixername[80]; /* mixer name */
char components[128]; /* card components delimited with
space */
struct module *module; /* top-level module */
void *private_data; /* private data for soundcard */
void (*private_free) (struct snd_card *card); /* callback for freeing of
private data */
struct list_head devices; /* devices */
unsigned int last_numid; /* last used numeric ID */
struct rw_semaphore controls_rwsem; /* controls list lock */
rwlock_t ctl_files_rwlock; /* ctl_files list lock */
int controls_count; /* count of all controls */
int user_ctl_count; /* count of all user controls */
struct list_head controls; /* all controls for this card */
struct list_head ctl_files; /* active control files */
struct snd_info_entry *proc_root; /* root for soundcard specific files */
struct snd_info_entry *proc_id; /* the card id */
struct proc_dir_entry *proc_root_link; /* number link to real id */
struct list_head files_list; /* all files associated to this card */
struct snd_shutdown_f_ops *s_f_ops; /* file operations in the shutdown
state */
spinlock_t files_lock; /* lock the files for this card */
int shutdown; /* this card is going down */
int free_on_last_close; /* free in context of file_release */
wait_queue_head_t shutdown_sleep;
struct device *dev; /* device assigned to this card */
#ifndef CONFIG_SYSFS_DEPRECATED
struct device *card_dev; /* cardX object for sysfs */
#endif
#ifdef CONFIG_PM
unsigned int power_state; /* power state */
struct mutex power_lock; /* power lock */
wait_queue_head_t power_sleep;
#endif
#if defined(CONFIG_SND_MIXER_OSS) || defined(CONFIG_SND_MIXER_OSS_MODULE)
struct snd_mixer_oss *mixer_oss;
int mixer_oss_change_count;
#endif
};
struct list_head devices 记录该声卡下所有逻辑设备的链表
struct list_head controls 记录该声卡下所有的控制单元的链表
void *private_data 声卡的私有数据，可以在创建声卡时通过参数指定数据的大小
2. 声卡的建立流程
2.1.1. 第一步，创建snd_card的一个实例
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int err;
....
err = snd_card_create(index, id, THIS_MODULE, 0, &card);
index 一个整数值，该声卡的编号
id 字符串，声卡的标识符
第四个参数 该参数决定在创建snd_card实例时，需要同时额外分配的私有数据的大小，该数据的指针最终会赋值给snd_card的private_data数据成员
card 返回所创建的snd_card实例的指针
strcpy(card->driver, "My Chip");
strcpy(card->shortname, "My Own Chip 123");
sprintf(card->longname, "%s at 0x%lx irq %i",
card->shortname, chip->ioport, chip->irq);
/**
* snd_card_create - create and initialize a soundcard structure
* @idx: card index (address) [0 ... (SNDRV_CARDS-1)]
* @xid: card identification (ASCII string)
* @module: top level module for locking
* @extra_size: allocate this extra size after the main soundcard structure
* @card_ret: the pointer to store the created card instance
*
* Creates and initializes a soundcard structure.
*
* The function allocates snd_card instance via kzalloc with the given
* space for the driver to use freely. The allocated struct is stored
* in the given card_ret pointer.
*
* Returns zero if successful or a negative error code.
*/
int snd_card_create(int idx, const char *xid,
struct module *module, int extra_size,
struct snd_card **card_ret)
/* the control interface cannot be accessed from the user space until */
/* snd_cards_bitmask and snd_cards are set with snd_card_register */
err = snd_ctl_create(card);
/**
* snd_card_register - register the soundcard
* @card: soundcard structure
*
* This function registers all the devices assigned to the soundcard.
* Until calling this, the ALSA control interface is blocked from the
* external accesses. Thus, you should call this function at the end
* of the initialization of the card.
*
* Returns zero otherwise a negative error code if the registrain failed.
*/
int snd_card_register(struct snd_card *card)
首先，创建sysfs下的设备：
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if (!card->card_dev) {
card->card_dev = device_create(sound_class, card->dev,
MKDEV(0, 0), card,
"card%i", card->number);
if (IS_ERR(card->card_dev))
card->card_dev = NULL;
}
其中，sound_class是在/sound/sound_core.c中创建的：
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static char *sound_devnode(struct device *dev, mode_t *mode)
{
if (MAJOR(dev->devt) == SOUND_MAJOR)
return NULL;
return kasprintf(GFP_KERNEL, "snd/%s", dev_name(dev));
}
static int __init init_soundcore(void)
{
int rc;
rc = init_oss_soundcore();
if (rc)
return rc;
sound_class = class_create(THIS_MODULE, "sound");
if (IS_ERR(sound_class)) {
cleanup_oss_soundcore();
return PTR_ERR(sound_class);
}
sound_class->devnode = sound_devnode;
return 0;
}
全局的capture和playback “Capture Source"，"Capture Volume"，"Capture Switch"，它们用于全局的capture source，switch和volume。同理，"Playback Volume"，"Playback Switch"，它们用于全局的输出switch和volume。
Tone-controles 音调控制的开关和音量命名为：Tone Control - XXX，例如，"Tone Control - Switch"，"Tone Control - Bass"，"Tone Control - Center"。
3D controls 3D控件的命名规则：，"3D Control - Switch"，"3D Control - Center"，"3D Control - Space"。
Mic boost 麦克风音量加强控件命名为："Mic Boost"或"Mic Boost(6dB)"。
/* Allocate and load the module: note that size of section 0 is always
zero, and we rely on this for optional sections. */
static int load_module(struct load_info *info, const char __user *uargs,
int flags)
{
struct module *mod;
struct module_ext *mod_ext;
long err;
err = module_sig_check(info);
if (err)
goto free_copy;
...
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static int module_sig_check(struct load_info *info)
{
int err = -ENOKEY;
const unsigned long markerlen = sizeof(MODULE_SIG_STRING) - 1;
const void *mod = info->hdr;
# 模块最后是 MODULE_SIG_STRING 字符串
if (info->len > markerlen &&
memcmp(mod + info->len - markerlen, MODULE_SIG_STRING, markerlen) == 0) {
/* We truncate the module to discard the signature */
info->len -= markerlen;
err = mod_verify_sig(mod, &info->len); // 检验签名
}
if (!err) {
info->sig_ok = true;
return 0;
}
/* Not having a signature is only an error if we're strict. */
if ((err == -ENOKEY && !sig_enforce) && (get_securelevel() <= 0))
err = 0;
return err;
}
obj-$(CONFIG_SYSTEM_TRUSTED_KEYRING) += system_keyring.o system_certificates.o
...
...
###############################################################################
#
# Roll all the X.509 certificates that we can find together and pull them into
# the kernel so that they get loaded into the system trusted keyring during
# boot.
#
# We look in the source root and the build root for all files whose name ends
# in ".x509". Unfortunately, this will generate duplicate filenames, so we
# have make canonicalise the pathnames and then sort them to discard the
# duplicates.
#
###############################################################################
ifeq ($(CONFIG_SYSTEM_TRUSTED_KEYRING),y)
X509_CERTIFICATES-y := $(wildcard *.x509) $(wildcard $(srctree)/*.x509)
X509_CERTIFICATES-$(CONFIG_MODULE_SIG) += signing_key.x509
X509_CERTIFICATES := $(sort $(foreach CERT,$(X509_CERTIFICATES-y), \
$(or $(realpath $(CERT)),$(CERT))))
X509_TOOL_CERTIFICATES := $(wildcard $(srctree)/tool_certs/*.pub)
ifeq ($(X509_CERTIFICATES),)
$(warning *** No X.509 certificates found ***)
endif
ifneq ($(wildcard $(obj)/.x509.list),)
ifneq ($(shell cat $(obj)/.x509.list),$(X509_CERTIFICATES))
$(info X.509 certificate list changed)
$(shell rm $(obj)/.x509.list)
endif
endif
ifneq ($(wildcard $(obj)/.tool_x509.list),)
ifneq ($(shell cat $(obj)/.tool_x509.list),$(X509_TOOL_CERTIFICATES))
$(info X.509 tool_certificate list changed)
$(shell rm $(obj)/.tool_x509.list)
endif
endif
kernel/system_certificates.o: $(obj)/x509_certificate_list $(obj)/x509_tool_certificate_list
quiet_cmd_x509certs = CERTS $@
cmd_x509certs = cat $(X509_CERTIFICATES) /dev/null >$@ $(foreach X509,$(X509_CERTIFICATES),; echo " - Including cert $(X509)")
quiet_cmd_tool_x509certs = CERTS $@
cmd_tool_x509certs = cat $(X509_TOOL_CERTIFICATES) /dev/null >$@ $(foreach X509,$(X509_TOOL_CERTIFICATES),; echo " - Including cert $(X509)")
targets += $(obj)/x509_certificate_list
$(obj)/x509_certificate_list: $(X509_CERTIFICATES) $(obj)/.x509.list
$(call if_changed,x509certs)
Linux 密钥保留服务（Linux key retention service）是在 Linux 2.6 中引入的，它的主要意图是在 Linux 内核中缓存身份验证数据。远程文件系统和其他内核服务可以使用这个服务来管理密码学、身份验证标记、跨域用户映射和其他安全问题。它还使 Linux 内核能够快速访问所需的密钥，并可以用来将密钥操作（比如添加、更新和删除）委托给用户空间。
本文将概述 Linux 密钥保留服务，定义它的术语，帮助您快速掌握 Linux 密钥的使用方法。您将通过示例代码了解如何在内核模块中使用 Linux 密钥保留服务。在编写本文时使用的内核版本是 2.6.20。
什么是密钥？
密钥（key）是一组密码学数据、身份验证标记或某些相似的元素，它在内核中由 struct key 表示。在 Linux 内核源代码中，struct key 是在 include/linux/key.h 下定义的。
root@phoenix set.5]# insmod ./kernel.land/newkey.ko
oading the module ...
egistered "learning_key"
接下来，执行用户级程序。
清单 8. 执行用户级程序
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root@phoenix set.5]# ./user.land/session
n /var/log/message, you will see similar output
nstalling session keyring:
eyring allocated successfully.
eyring instantiated and linked successfully.
ew session keyring installed successfully.
ey of new type allocated successfully.
ew key type linked to current session.
Linux 密钥保留服务是一种新的机制，其用途是保存与安全相关的信息，让 Linux 内核可以快速地访问这些信息。这个服务仍然处于初级阶段，刚刚开始获得认可。OpenAFS 使用 Linux 密钥保留服务来实现进程身份验证组（PAG），NFSv4 和 MIT Kerberos 也使用它。Linux 密钥保留服务仍然在进行开发，以后可能会修改或改进。
下载资源
使用 Linux 密钥保留服务的示例应用程序 (key.retention.services.zip | 4KB)
