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/*
 * 在内核<linux/circ_buf.h>中定义了关于环形缓冲区的相关变量。
 * 其中缓冲区的大小size必须定义成2的n次方，这样可以将取余运算转换成位与运算，
 * 提高计算机的处理速度。例如：x % size = x & (size - 1)。实际可用的空间为size-1，
 * 这样可以避免缓冲区为满时和为空时都满足head = tail。
*/
struct circ_buf {
	char *buf;	// 指向分配缓冲区起始地址的指针
	int head;   // 指向生产者向缓冲区放入数据的位置
	int tail;  	// 指向消费者从缓冲区取走数据的位置
};

/* Return count in buffer.  */
/* 计算缓冲区中有效数据的大小； */
#define CIRC_CNT(head,tail,size) (((head) - (tail)) & ((size)-1))

/* Return space available, 0..size-1.  We always leave one free char
   as a completely full buffer has head == tail, which is the same as
   empty.  */
/* 计算缓冲区剩余空闲空间的大小； */
#define CIRC_SPACE(head,tail,size) CIRC_CNT((tail),((head)+1),(size))

/* Return count up to the end of the buffer.  Carefully avoid
   accessing head and tail more than once, so they can change
   underneath us without returning inconsistent results.  */
/* 计算tail到缓冲区尾部的数据大小，即一次性可以读取的数据大小；*/
#define CIRC_CNT_TO_END(head,tail,size) \
	({int end = (size) - (tail); \
	  int n = ((head) + end) & ((size)-1); \
	  n < end ? n : end;})

/* Return space available up to the end of the buffer.  */
/* 计算head到缓冲区尾部的剩余空间，即一次性可以写入的数据大小； */
#define CIRC_SPACE_TO_END(head,tail,size) \
	({int end = (size) - 1 - (head); \
	  int n = (end + (tail)) & ((size)-1); \
	  n <= end ? n : end+1;})

/* 功能：    uart_register_driver用于将串口驱动uart_driver注册到内核(串口核心层)中，通常在模块初始化函数调用该函数。
 * 参数 drv：要注册的uart_driver

 * 返回值：  成功，返回0；否则返回错误码
 */
int uart_register_driver(struct uart_driver *drv)

/* 功能：    uart_unregister_driver用于注销我们已注册的uart_driver，通常在模块卸载函数调用该函数
 * 参数 drv：要注销的uart_driver

 * 返回值：  成功，返回0；否则返回错误码
 */
void uart_unregister_driver(struct uart_driver *drv)

/*
 * This structure describes all the operations that can be
 * done on the physical hardware.
 */
  struct uart_ops {
    unsigned int (*tx_empty)(struct uart_port *); /* 串口的Tx FIFO缓存是否为空。如果为空，函数应返回TIOCSER_TEMT，否则返回0。如果端口不支持此操作，返回TIOCSER_TEMT。*/
    void         (*set_mctrl)(struct uart_port *, unsigned int mctrl); /* 设置串口modem控制 */
    unsigned int (*get_mctrl)(struct uart_port *); /* 获取串口modem控制 */
    void         (*stop_tx)(struct uart_port *); /* 禁止串口发送数据 */
    void         (*start_tx)(struct uart_port *); /* 使能串口发送数据 */
    void         (*send_xchar)(struct uart_port *, char ch);/* 发送xChar */
    void         (*stop_rx)(struct uart_port *); /* 禁止串口接收数据 */
    void         (*enable_ms)(struct uart_port *); /* 使能modem的状态信号 */
    void         (*break_ctl)(struct uart_port *, int ctl); /* 设置break信号 */
    int          (*startup)(struct uart_port *); /* 启动串口,应用程序打开串口设备文件时,该函数会被调用 */
    void         (*shutdown)(struct uart_port *); /* 关闭串口,应用程序关闭串口设备文件时,该函数会被调用 */
    void         (*set_termios)(struct uart_port *, struct ktermios *new, struct ktermios *old); /* 设置串口参数 */
    void         (*pm)(struct uart_port *, unsigned int state,
             unsigned int oldstate); /* 串口电源管理 */
    int          (*set_wake)(struct uart_port *, unsigned int state); /*  */
    const char  *(*type)(struct uart_port *); /* 返回一描述串口类型的字符串 */
    void         (*release_port)(struct uart_port *); /* 释放串口已申请的IO端口/IO内存资源,必要时还需iounmap */
    int          (*request_port)(struct uart_port *); /* 申请必要的IO端口/IO内存资源,必要时还可以重新映射串口端口 */
    void         (*config_port)(struct uart_port *, int); /* 执行串口所需的自动配置 */
    int          (*verify_port)(struct uart_port *, struct serial_struct *); /* 核实新串口的信息 */
    int          (*ioctl)(struct uart_port *, unsigned int, unsigned long); /* IO控制 */
  };

struct uart_port {
    spinlock_t             lock;           /* 串口端口锁 */
    unsigned int           iobase;         /* IO端口基地址 */
    unsigned char __iomem *membase;        /* IO内存基地址,经映射(如ioremap)后的IO内存虚拟基地址 */
    unsigned int           irq;            /* 中断号 */
    unsigned int           uartclk;        /* 串口时钟 */
    unsigned int           fifosize;       /* 串口FIFO缓冲大小 */
    unsigned char          x_char;         /* xon/xoff字符 */
    unsigned char          regshift;       /* 寄存器位移 */
    unsigned char          iotype;         /* IO访问方式 */
    unsigned char          unused1;

#define UPIO_PORT        (0)               /* IO端口 */
#define UPIO_HUB6        (1)
#define UPIO_MEM         (2)               /* IO内存 */
#define UPIO_MEM32       (3)
#define UPIO_AU          (4)               /* Au1x00 type IO */
#define UPIO_TSI         (5)               /* Tsi108/109 type IO */
#define UPIO_DWAPB       (6)               /* DesignWare APB UART */
#define UPIO_RM9000      (7)               /* RM9000 type IO */

    unsigned int        read_status_mask;  /* 关心的Rx error status */
    unsigned int        ignore_status_mask;/* 忽略的Rx error status */
    struct uart_info      *info;           /* pointer to parent info */
    struct uart_icount     icount;         /* 计数器 */
    
    struct console        *cons;           /* console结构体 */
#ifdef CONFIG_SERIAL_CORE_CONSOLE
    unsigned long         sysrq;           /* sysrq timeout */
#endif

    upf_t                 flags;

#define UPF_FOURPORT         ((__force upf_t) (1 << 1))
#define UPF_SAK              ((__force upf_t) (1 << 2))
#define UPF_SPD_MASK         ((__force upf_t) (0x1030))
#define UPF_SPD_HI           ((__force upf_t) (0x0010))
#define UPF_SPD_VHI          ((__force upf_t) (0x0020))
#define UPF_SPD_CUST         ((__force upf_t) (0x0030))
#define UPF_SPD_SHI          ((__force upf_t) (0x1000))
#define UPF_SPD_WARP         ((__force upf_t) (0x1010))
#define UPF_SKIP_TEST        ((__force upf_t) (1 << 6))
#define UPF_AUTO_IRQ         ((__force upf_t) (1 << 7))
#define UPF_HARDPPS_CD       ((__force upf_t) (1 << 11))
#define UPF_LOW_LATENCY      ((__force upf_t) (1 << 13))
#define UPF_BUGGY_UART       ((__force upf_t) (1 << 14))
#define UPF_MAGIC_MULTIPLIER ((__force upf_t) (1 << 16))
#define UPF_CONS_FLOW        ((__force upf_t) (1 << 23))
#define UPF_SHARE_IRQ        ((__force upf_t) (1 << 24))
#define UPF_BOOT_AUTOCONF    ((__force upf_t) (1 << 28))
#define UPF_FIXED_PORT       ((__force upf_t) (1 << 29))
#define UPF_DEAD             ((__force upf_t) (1 << 30))
#define UPF_IOREMAP          ((__force upf_t) (1 << 31))

#define UPF_CHANGE_MASK      ((__force upf_t) (0x17fff))
#define UPF_USR_MASK         ((__force upf_t) (UPF_SPD_MASK|UPF_LOW_LATENCY))

    unsigned int             mctrl;        /* 当前的moden设置 */
    unsigned int             timeout;      /* character-based timeout */        
    unsigned int             type;         /* 端口类型 */
    const struct uart_ops   *ops;          /* 串口端口操作函数集 */
    unsigned int             custom_divisor;
    unsigned int             line;         /* 端口索引 uart_driver.dev_name加上line组成串口的设备节点的名字 */
    resource_size_t          mapbase;      /* IO内存物理基地址，可用于ioremap */
    struct device           *dev;          /* 父设备 */
    unsigned char            hub6;         /* this should be in the 8250 driver */
    unsigned char            suspended;
    unsigned char            unused[2];
    void                    *private_data; /* 端口私有数据,一般为platform数据指针 */
};

struct uart_driver {
    struct module     *owner;           /* 拥有该uart_driver的模块,一般为THIS_MODULE */
    const char        *driver_name;     /* 串口驱动名，串口设备文件名以驱动名为基础 */
    const char        *dev_name;        /* 串口设备名 */
    int                major;           /* 主设备号 */
    int                minor;           /* 次设备号 */
    int                nr;              /* 该uart_driver支持的串口个数(最大) */
    struct console    *cons;            /* 其对应的console.若该uart_driver支持serial console,否则为NULL */

    /*
     * these are private; the low level driver should not
     * touch these; they should be initialised to NULL
     */
    struct uart_state *state;
    struct tty_driver *tty_driver;
};

/*
 * This struct defines a memory VMM memory area. There is one of these
 * per VM-area/task.  A VM area is any part of the process virtual memory
 * space that has a special rule for the page-fault handlers (ie a shared
 * library, the executable area etc).
 * 此结构定义了内存VMM内存区域。 每个VM区域/任务中有一个。 VM区域是进程虚拟内存空间的任何部分，
 * 它具有页面错误处理程序的特殊规则（即共享库，可执行区域等）。
 */
struct vm_area_struct {
	/* The first cache line has the info for VMA tree walking.
	   第一个缓存行具有VMA树移动的信息 */
	
	unsigned long vm_start;		/* Our start address within vm_mm. 我们的起始地址在vm_mm内*/
	unsigned long vm_end;		/* The first byte after our end address within vm_mm. 我们的结束地址在vm_mm之后的第一个字节*/

	/* linked list of VM areas per task, sorted by address 
	   每个任务的VM区域的链接列表，按地址排序  */
	struct vm_area_struct *vm_next, *vm_prev;

	struct rb_node vm_rb;

	/*
	 * Largest free memory gap in bytes to the left of this VMA.
	 * Either between this VMA and vma->vm_prev, or between one of the
	 * VMAs below us in the VMA rbtree and its ->vm_prev. This helps
	 * get_unmapped_area find a free area of the right size.
	 * 此VMA左侧最大的可用内存间隙（以字节为单位）。在此VMA和vma-> vm_prev之间，
	 * 或者在VMA rbtree中我们下面的一个VMA与其->vm_prev之间。
	 * 这有助于get_unmapped_area找到合适大小的空闲区域。
	 */
	unsigned long rb_subtree_gap;

	/* Second cache line starts here. 
	   第二个缓存行从这里开始 */

	struct mm_struct *vm_mm;	/* The address space we belong to. 我们所属的address space*/
	pgprot_t vm_page_prot;		/* Access permissions of this VMA. 此VMA的访问权限 */
	unsigned long vm_flags;		/* Flags, see mm.h. */

	/*
	 * For areas with an address space and backing store,
	 * linkage into the address_space->i_mmap interval tree.
	 * 对于具有地址空间（address apace）和后备存储(backing store)的区域，
	 * 链接到address_space->i_mmap间隔树，或者链接到address_space-> i_mmap_nonlinear列表中的vma。
	 */
	struct {
		struct rb_node rb;
		unsigned long rb_subtree_last;
	} shared;

	/*
	 * A file's MAP_PRIVATE vma can be in both i_mmap tree and anon_vma
	 * list, after a COW of one of the file pages.	A MAP_SHARED vma
	 * can only be in the i_mmap tree.  An anonymous MAP_PRIVATE, stack
	 * or brk vma (with NULL file) can only be in an anon_vma list.
	 * 在其中一个文件页面的COW之后，文件的MAP_PRIVATE vma可以在i_mmap树和anon_vma列表中。
	 * MAP_SHARED vma只能位于i_mmap树中。
	 * 匿名MAP_PRIVATE，堆栈或brk vma（带有NULL文件）只能位于anon_vma列表中。
	 */
	struct list_head anon_vma_chain; /* Serialized by mmap_sem &
					  * page_table_lock 由mmap_sem和* page_table_lock序列化*/
	struct anon_vma *anon_vma;	/* Serialized by page_table_lock 由page_table_lock序列化*/

	/* Function pointers to deal with this struct. 
	   用于处理此结构体的函数指针 */
	const struct vm_operations_struct *vm_ops;

	/* Information about our backing store: 
	   后备存储（backing store）的信息:*/
	unsigned long vm_pgoff;		/* Offset (within vm_file) in PAGE_SIZE units 以PAGE_SIZE为单位的偏移量（在vm_file中）*/
	struct file * vm_file;		/* File we map to (can be NULL). 我们映射到文件（可以为NULL）*/
	void * vm_private_data;		/* was vm_pte (shared mem) 是vm_pte（共享内存） */

	atomic_long_t swap_readahead_info;
#ifndef CONFIG_MMU
	struct vm_region *vm_region;	/* NOMMU mapping region NOMMU映射区域  */
#endif
#ifdef CONFIG_NUMA
	struct mempolicy *vm_policy;	/* NUMA policy for the VMA 针对VMA的NUMA政策 */
#endif
	struct vm_userfaultfd_ctx vm_userfaultfd_ctx;
} __randomize_layout;

int remap_pfn_range(struct vm_area_struct *, unsigned long addr,
            unsigned long pfn, unsigned long size, pgprot_t);

#define SetPageReserved(page) set_bit(PG_reserved,&(page)->flags)

/*
引用计数的实现结构体
*/
  
 
#ifndef _KREF_H_
#define _KREF_H_
 
#ifdef __KERNEL__
 
#include <linux/types.h>
#include <asm/atomic.h>
 
/* 引用计数的原理很简单，使用时加1，不用时减1，如果减为0
 则调用释放函数。
*/
struct kref {
/* Linux 使用原子变量来计数，这样可以防止多CPU，多进程时的竞态现象发生 */
    atomic_t refcount;
};
 
void kref_init(struct kref *kref);/* 初始化一个引用计数结构体 */
void kref_get(struct kref *kref);/* 增加一个引用计数 */
void kref_put(struct kref *kref, void (*release) (struct kref *kref));/* 减少一个引用计数 */
 
#endif /* __KERNEL__ */
#endif /* _KREF_H_ */

#include <linux/kref.h>
#include <linux/module.h>
 
/**
 * kref_init - initialize object.
 * @kref: object in question.
 */
 /* 初始化一个引用计数，这里可以看到引用计数初始化为1 */
void kref_init(struct kref *kref)
{
    atomic_set(&kref->refcount,1);
}
 
/**
 * kref_get - increment refcount for object.
 * @kref: object.
 */
 /* 增加一个引用计数，可以发现这里是原子操作 */
void kref_get(struct kref *kref)
{
    WARN_ON(!atomic_read(&kref->refcount));
    atomic_inc(&kref->refcount);
}
 
/**
 * kref_put - decrement refcount for object.
 * @kref: object.
 * @release: pointer to the function that will clean up the object when the
 *       last reference to the object is released.
 *       This pointer is required, and it is not acceptable to pass kfree
 *       in as this function.
 *
 * Decrement the refcount, and if 0, call release().
 */
;/* 减少一个引用计数 */
void kref_put(struct kref *kref, void (*release) (struct kref *kref))
{
    WARN_ON(release == NULL);
    WARN_ON(release == (void (*)(struct kref *))kfree);
 
    if (atomic_dec_and_test(&kref->refcount))
        release(kref);/* 如果引用计数为0，就调用释放函数 */
}