设备驱动杂记

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1、大部分的编程问题其实可以划分为2个部分，提供什么能力（机制）和如何使用这些能力（策略）。如果这两方面由程序的不同部分来表达，或者甚至由不同的程序共同表达，软件包时非常揉弄故意开发和适应特殊的需求。

2、一个设备驱动可以只包含<linux/sched.h>并且引用当前进程。

3、在内核中可以通过包含头文件<linux/sched.h>后使用current来使用当前进程的信息。

例如，下面的语句打印了当前进程的进程ID和命令名称。

Printk(KERN_INFO “The process is /” %s/” (pid %i) /n”),current->comm.,current->pid);

Current并不是一个真正的全局变量，它定义在arch/***/include/asm的current.h文件中，定义如下：

static __always_inline struct task_struct *get_current(void)

{

return percpu_read_stable(current_task);

}

#define current get_current()

以上定义使得current为指向task_struct结构的指针。

Task_struct结构如下：

structtask_struct {

volatilelong state; /* -1 unrunnable, 0 runnable,>0 stopped */

void*stack;

atomic_tusage;

unsignedint flags; /* per process flags, definedbelow */

unsignedint ptrace;

intlock_depth; /* BKL lockdepth */

#ifdef CONFIG_SMP

#ifdef __ARCH_WANT_UNLOCKED_CTXSW

intoncpu;

#endif

intprio, static_prio, normal_prio;

unsignedint rt_priority;

conststruct sched_class *sched_class;

structsched_entity se;

structsched_rt_entity rt;

#ifdef CONFIG_PREEMPT_NOTIFIERS

/*list of struct preempt_notifier: */

structhlist_head preempt_notifiers;

#endif

* fpu_counter contains the number ofconsecutive context switches

* that the FPU is used. If this is over athreshold, the lazy fpu

* saving becomes unlazy to save the trap. Thisis an unsigned char

* so that after 256 times the counter wrapsand the behavior turns

* lazy again; this to deal with bursty appsthat only use FPU for

* a short time

unsignedchar fpu_counter;

#ifdef CONFIG_BLK_DEV_IO_TRACE

unsignedint btrace_seq;

#endif

unsignedint policy;

cpumask_tcpus_allowed;

#ifdef CONFIG_TREE_PREEMPT_RCU

intrcu_read_lock_nesting;

charrcu_read_unlock_special;

structrcu_node *rcu_blocked_node;

structlist_head rcu_node_entry;

#endif /* #ifdef CONFIG_TREE_PREEMPT_RCU*/

#if defined(CONFIG_SCHEDSTATS) ||defined(CONFIG_TASK_DELAY_ACCT)

structsched_info sched_info;

#endif

structlist_head tasks;

structplist_node pushable_tasks;

structmm_struct *mm, *active_mm;

#if defined(SPLIT_RSS_COUNTING)

structtask_rss_stat rss_stat;

#endif

/* task state */

intexit_state;

intexit_code, exit_signal;

intpdeath_signal; /* The signal sent when the parent dies */

/*??? */

unsignedint personality;

unsigneddid_exec:1;

unsignedin_execve:1; /* Tell the LSMs that theprocess is doing an

* execve */

unsignedin_iowait:1;

/*Revert to default priority/policy when forking */

unsignedsched_reset_on_fork:1;

//进程标识号

//在内核中pid对进程而言是进程号，对于线程而言是线程号，同一进程的不同线程的pid是不同的，但是同一进程的不同线程有统一的tgid

pid_tpid;

pid_ttgid;

#ifdef CONFIG_CC_STACKPROTECTOR

/*Canary value for the -fstack-protector gcc feature */

unsignedlong stack_canary;

#endif

* pointers to (original) parent process,youngest child, younger sibling,

* older sibling, respectively. (p->father can be replaced with

* p->real_parent->pid)

structtask_struct *real_parent; /* real parent process */

structtask_struct *parent; /* recipient of SIGCHLD, wait4() reports */

* children/sibling forms the list of mynatural children

structlist_head children; /* list of mychildren */

structlist_head sibling; /* linkage in myparent's children list */

structtask_struct *group_leader; /* threadgroupleader */

* ptraced is the list of tasks this task isusing ptrace on.

* This includes both natural children andPTRACE_ATTACH targets.

* p->ptrace_entry is p's link on thep->parent->ptraced list.

structlist_head ptraced;

structlist_head ptrace_entry;

* This is the tracer handle for the ptrace BTSextension.

* This field actually belongs to the ptracertask.

structbts_context *bts;

/*PID/PID hash table linkage. */

structpid_link pids[PIDTYPE_MAX];

structlist_head thread_group;

structcompletion *vfork_done; /*for vfork() */

int__user *set_child_tid; /*CLONE_CHILD_SETTID */

int__user *clear_child_tid; /*CLONE_CHILD_CLEARTID */

cputime_tutime, stime, utimescaled, stimescaled;

cputime_tgtime;

#ifndef CONFIG_VIRT_CPU_ACCOUNTING

cputime_tprev_utime, prev_stime;

#endif

unsignedlong nvcsw, nivcsw; /* context switch counts */

structtimespec start_time; /*monotonic time */

structtimespec real_start_time; /* boot basedtime */

/* mm fault and swap info: this canarguably be seen as either mm-specific or thread-specific */

unsignedlong min_flt, maj_flt;

structtask_cputime cputime_expires;

structlist_head cpu_timers[3];

/* process credentials */

conststruct cred *real_cred; /* objective andreal subjective task

* credentials (COW) */

conststruct cred *cred; /* effective(overridable) subjective task

* credentials (COW) */

structmutex cred_guard_mutex; /* guard againstforeign influences on

* credential calculations

* (notably. ptrace) */

structcred *replacement_session_keyring; /* for KEYCTL_SESSION_TO_PARENT */

//进程正在运行的可执行文件名称

charcomm[TASK_COMM_LEN]; /* executable name excluding path

- access with [gs]et_task_comm (which lock

it with task_lock())

- initialized normally by setup_new_exec*/

/* file system info */

intlink_count, total_link_count;

#ifdef CONFIG_SYSVIPC

/* ipc stuff */

structsysv_sem sysvsem;

#endif

#ifdef CONFIG_DETECT_HUNG_TASK

/* hung task detection */

unsignedlong last_switch_count;

#endif

/* CPU-specific state of this task */

structthread_struct thread;

/* filesystem information */

structfs_struct *fs;

/* open file information */

structfiles_struct *files;

/* namespaces */

structnsproxy *nsproxy;

/* signal handlers */

structsignal_struct *signal;

structsighand_struct *sighand;

sigset_tblocked, real_blocked;

sigset_tsaved_sigmask; /* restored ifset_restore_sigmask() was used */

structsigpending pending;

unsignedlong sas_ss_sp;

size_tsas_ss_size;

int(*notifier)(void *priv);

void*notifier_data;

sigset_t*notifier_mask;

structaudit_context *audit_context;

#ifdef CONFIG_AUDITSYSCALL

uid_tloginuid;

unsignedint sessionid;

#endif

seccomp_tseccomp;

/* Thread group tracking */

u32 parent_exec_id;

u32 self_exec_id;

/* Protection of (de-)allocation: mm,files, fs, tty, keyrings, mems_allowed,

*mempolicy */

spinlock_talloc_lock;

#ifdef CONFIG_GENERIC_HARDIRQS

/*IRQ handler threads */

structirqaction *irqaction;

#endif

/*Protection of the PI data structures: */

raw_spinlock_tpi_lock;

#ifdef CONFIG_RT_MUTEXES

/*PI waiters blocked on a rt_mutex held by this task */

structplist_head pi_waiters;

/*Deadlock detection and priority inheritance handling */

structrt_mutex_waiter *pi_blocked_on;

#endif

#ifdef CONFIG_DEBUG_MUTEXES

/*mutex deadlock detection */

structmutex_waiter *blocked_on;

#endif

#ifdef CONFIG_TRACE_IRQFLAGS

unsignedint irq_events;

unsignedlong hardirq_enable_ip;

unsignedlong hardirq_disable_ip;

unsignedint hardirq_enable_event;

unsignedint hardirq_disable_event;

inthardirqs_enabled;

inthardirq_context;

unsignedlong softirq_disable_ip;

unsignedlong softirq_enable_ip;

unsignedint softirq_disable_event;

unsignedint softirq_enable_event;

intsoftirqs_enabled;

intsoftirq_context;

#endif

#ifdef CONFIG_LOCKDEP

# define MAX_LOCK_DEPTH 48UL

u64curr_chain_key;

intlockdep_depth;

unsignedint lockdep_recursion;

structheld_lock held_locks[MAX_LOCK_DEPTH];

gfp_tlockdep_reclaim_gfp;

#endif

/* journalling filesystem info */

void*journal_info;

/* stacked block device info */

structbio_list *bio_list;

/* VM state */

structreclaim_state *reclaim_state;

structbacking_dev_info *backing_dev_info;

structio_context *io_context;

unsignedlong ptrace_message;

siginfo_t*last_siginfo; /* For ptrace use. */

structtask_io_accounting ioac;

#if defined(CONFIG_TASK_XACCT)

u64acct_rss_mem1; /* accumulated rssusage */

u64acct_vm_mem1; /* accumulated virtualmemory usage */

cputime_tacct_timexpd; /* stime + utimesince last update */

#endif

#ifdef CONFIG_CPUSETS

nodemask_tmems_allowed; /* Protected by alloc_lock*/

intcpuset_mem_spread_rotor;

#endif

#ifdef CONFIG_CGROUPS

/*Control Group info protected by css_set_lock */

structcss_set *cgroups;

/*cg_list protected by css_set_lock and tsk->alloc_lock */

structlist_head cg_list;

#endif

#ifdef CONFIG_FUTEX

structrobust_list_head __user *robust_list;

#ifdef CONFIG_COMPAT

structcompat_robust_list_head __user *compat_robust_list;

#endif

structlist_head pi_state_list;

structfutex_pi_state *pi_state_cache;

#endif

#ifdef CONFIG_PERF_EVENTS

structperf_event_context *perf_event_ctxp;

structmutex perf_event_mutex;

structlist_head perf_event_list;

#endif

#ifdef CONFIG_NUMA

structmempolicy *mempolicy; /* Protectedby alloc_lock */

shortil_next;

#endif

atomic_tfs_excl; /* holding fs exclusiveresources */

structrcu_head rcu;

* cache last used pipe for splice

structpipe_inode_info *splice_pipe;

#ifdef CONFIG_TASK_DELAY_ACCT

structtask_delay_info *delays;

#endif

#ifdef CONFIG_FAULT_INJECTION

intmake_it_fail;

#endif

structprop_local_single dirties;

#ifdef CONFIG_LATENCYTOP

intlatency_record_count;

structlatency_record latency_record[LT_SAVECOUNT];

#endif

* time slack values; these are used to roundup poll() and

* select() etc timeout values. These are innanoseconds.

unsignedlong timer_slack_ns;

unsignedlong default_timer_slack_ns;

structlist_head *scm_work_list;

#ifdef CONFIG_FUNCTION_GRAPH_TRACER

/*Index of current stored address in ret_stack */

intcurr_ret_stack;

/*Stack of return addresses for return function tracing */

structftrace_ret_stack *ret_stack;

/*time stamp for last schedule */

unsignedlong long ftrace_timestamp;

* Number of functions that haven't been traced

* because of depth overrun.

atomic_ttrace_overrun;

/*Pause for the tracing */

atomic_ttracing_graph_pause;

#endif

#ifdef CONFIG_TRACING

/*state flags for use by tracers */

unsignedlong trace;

/*bitmask of trace recursion */

unsignedlong trace_recursion;

#endif /* CONFIG_TRACING */

#ifdef CONFIG_CGROUP_MEM_RES_CTLR /*memcg uses this to do batch job */

structmemcg_batch_info {

intdo_batch; /* incremented when batchuncharge started */

structmem_cgroup *memcg; /* target memcg of uncharge */

unsignedlong bytes; /* unchargedusage */

unsignedlong memsw_bytes; /* uncharged mem+swap usage */

}memcg_batch;

#endif

};

4、 lsmod通过读取/proc/modules虚拟文件工作，当前加载的模块的信息也可在位于/sys/module的sysfs虚拟文件系统中找到。

5、查看一个内核模块***.ko究竟包含哪些符号？

nm –l ***.ko

6、查看内核符号表

cat /proc/kallsyms

7、导出符号的两种方式：

EXPORT_SYMBOL(get_process_info);

EXPORT_SYMBOL_GPL(get_process_info_gpl);

8、查看模块信息

modinfo ***.ko

9、内核加载时传递参数

需要如下几个步骤：

<1>、在内核中添加如下语句：

static char * whom = "xu_guo";

int howmany =1;

module_param(whom,charp,S_IRUGO);

module_param(howmany,int,S_IRUGO);

<2>、加载时如下方式执行：

Insmod e1.ko whom=”xu”howmany=10 <enter>

10、模块加载时的数组参数传递方式：

Module_param_array(name,type,num,perm);

如果确实需要一个没有出现在上面列表中的类型，在模块代码里有钩子会允许你来定义它们。