Linux驅(qū)動(dòng)程序剛接觸，雖然不是很清楚，但是總歸是慢慢學(xué)習(xí)的過(guò)程。我的環(huán)境是Fedora14虛擬機(jī)。內(nèi)核版本是2.6.38.1，其中的實(shí)現(xiàn)過(guò)程存在很多的問(wèn)題，主要是因?yàn)楹芏嗟膬?nèi)核函數(shù)發(fā)生了較大的差別.其中最大的可能是ioctl以及互信息量的實(shí)現(xiàn)。這兩個(gè)的問(wèn)題也使得我們?cè)隍?qū)動(dòng)設(shè)計(jì)過(guò)程中出現(xiàn)很多的疑惑和問(wèn)題。
接上一部分，繼續(xù)總結(jié)：
主要包括幾個(gè)重要的結(jié)構(gòu)體、并發(fā)控制、以及ioctl的實(shí)現(xiàn)。在驅(qū)動(dòng)的設(shè)計(jì)過(guò)程主要涉及3個(gè)重要的結(jié)構(gòu)體。struct file_operations,struct inode,struct file.
struct file_operations主要是涉及一些文件操作的函數(shù)，其本質(zhì)上就是一個(gè)函數(shù)指針的集合，包含了文件操作的各種函數(shù)聲明，可能與應(yīng)用程序設(shè)計(jì)中的相應(yīng)函數(shù)只在參數(shù)上存在一定的差別。但是在2.6.36版本以后，其中的內(nèi)容發(fā)生了較大的變化，主要設(shè)計(jì)了ioctl的相關(guān)操作。
struct file_operations {
struct module *owner;
loff_t (*llseek) (struct file *, loff_t, int);
ssize_t (*read) (struct file *, char __user *, size_t, loff_t *);
ssize_t (*write) (struct file *, const char __user *, size_t, loff_t *);
ssize_t (*aio_read) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
ssize_t (*aio_write) (struct kiocb *, const struct iovec *, unsigned long, loff_t);
int (*readdir) (struct file *, void *, filldir_t);
unsigned int (*poll) (struct file *, struct poll_table_struct *);
/*新添加的函數(shù)，同時(shí)去掉了ioctl的函數(shù)，同時(shí)返回值也發(fā)生了變化*/
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
int (*mmap) (struct file *, struct vm_area_struct *);
int (*open) (struct inode *, struct file *);
int (*flush) (struct file *, fl_owner_t id);
int (*release) (struct inode *, struct file *);
int (*fsync) (struct file *, int datasync);
int (*aio_fsync) (struct kiocb *, int datasync);
int (*fasync) (int, struct file *, int);
int (*lock) (struct file *, int, struct file_lock *);
ssize_t (*sendpage) (struct file *, struct page *, int, size_t, loff_t *, int);
unsigned long (*get_unmapped_area)(struct file *, unsigned long, unsigned long, unsigned long, unsigned long);
int (*check_flags)(int);
int (*flock) (struct file *, int, struct file_lock *);
ssize_t (*splice_write)(struct pipe_inode_info *, struct file *, loff_t *, size_t, unsigned int);
ssize_t (*splice_read)(struct file *, loff_t *, struct pipe_inode_info *, size_t, unsigned int);
int (*setlease)(struct file *, long, struct file_lock **);
long (*fallocate)(struct file *file, int mode, loff_t offset,
loff_t len);
};
long (*unlocked_ioctl) (struct file *, unsigned int, unsigned long);
long (*compat_ioctl) (struct file *, unsigned int, unsigned long);
是最近添加進(jìn)來(lái)的函數(shù)，為了實(shí)現(xiàn)原來(lái)的ioctl函數(shù)，同時(shí)參數(shù)以及返回值都發(fā)生了較大的變化，這也是為什么在2.6.36版本以后的內(nèi)核中使用ioctl函數(shù)會(huì)報(bào)錯(cuò)的原因。unlocked_ioctl函數(shù)通常用來(lái)實(shí)現(xiàn)原來(lái)的ioctl函數(shù)，而compat_ioctl函數(shù)則用來(lái)實(shí)現(xiàn)一些兼容版本的ioctl問(wèn)題。返回值由原來(lái)的int變?yōu)閘ong型，也是需要注意的。在ioctl中，第一個(gè)參數(shù)是struct inode,2.6.36以后的版本將不能直接訪問(wèn)到inode參數(shù)，只能間接的訪問(wèn)，具體的訪問(wèn)方法后面在總結(jié)。
在驅(qū)動(dòng)實(shí)現(xiàn)過(guò)程中主要包括對(duì)各個(gè)需要實(shí)現(xiàn)函數(shù)的賦值，但是open函數(shù)不能賦值與否，都會(huì)默認(rèn)打開(kāi)，如果不賦值，則默認(rèn)該設(shè)備一直打開(kāi)。其他的函數(shù)不賦值，即表示不實(shí)現(xiàn)該方法。常用的復(fù)制方法如下：
/*添加該模塊的基本文件操作支持*/
static const struct file_operations mem_fops =
{
/*結(jié)尾不是分號(hào)，注意其中的差別*/
.owner = THIS_MODULE,
.llseek = mem_llseek,
.read = mem_read,
.write = mem_write,
.open = mem_open,
.release = mem_release,
/*添加新的操作支持*/
.unlocked_ioctl = mem_ioctl,
};
需要注意的是后面不再是分號(hào)，而是逗號(hào)。其中的mem_read、mem_write等是函數(shù)的具體實(shí)現(xiàn)過(guò)程。.owner表示該結(jié)構(gòu)體屬于那個(gè)，當(dāng)然就是THIS_MODULE,表示這個(gè)模塊。
struct inode表示的是一個(gè)文件的索引，該結(jié)構(gòu)是每一個(gè)具體的物理文件（保存在存儲(chǔ)器中的實(shí)體文件）的索引，一個(gè)文件對(duì)應(yīng)一個(gè)唯一的struct inode，其中表明了文件的大小，文件的類型，文件的時(shí)間等參數(shù)，結(jié)構(gòu)體中每一個(gè)參數(shù)都能表示某一個(gè)文件的特性，通過(guò)inode就能表示文件的所有信息。
struct inode {
/* RCU path lookup touches following: */
umode_t i_mode;
/*使用者的id*/
uid_t i_uid;
/*使用者的組的id*/
gid_t i_gid;
const struct inode_operations *i_op;
struct super_block *i_sb;
spinlock_t i_lock; /* i_blocks, i_bytes, maybe i_size */
unsigned int i_flags;
struct mutex i_mutex;
/*狀態(tài)標(biāo)志*/
unsigned long i_state;
unsigned long dirtied_when; /* jiffies of first dirtying */
struct hlist_node i_hash;
struct list_head i_wb_list; /* backing dev IO list */
struct list_head i_lru; /* inode LRU list */
struct list_head i_sb_list;
union {
struct list_head i_dentry;
struct rcu_head i_rcu;
};
unsigned long i_ino;
/*引用次數(shù)，當(dāng)這個(gè)數(shù)為0時(shí)，release函數(shù)才能完成*/
atomic_t i_count;
unsigned int i_nlink;
/*設(shè)備文件的設(shè)備號(hào)*/
dev_t i_rdev;
unsigned int i_blkbits;
u64 i_version;
/*文件偏移量*/
loff_t i_size;
#ifdef __NEED_I_SIZE_ORDERED
seqcount_t i_size_seqcount;
#endif
/*文件的時(shí)間參數(shù)，包括三種時(shí)間*/
struct timespec i_atime;
struct timespec i_mtime;
struct timespec i_ctime;
blkcnt_t i_blocks;
unsigned short i_bytes;
struct rw_semaphore i_alloc_sem;
const struct file_operations *i_fop; /* former ->i_op->default_file_ops */
struct file_lock *i_flock;
/*文件的備份地址空間*/
struct address_space *i_mapping;
/*設(shè)備地址空間*/
struct address_space i_data;
#ifdef CONFIG_QUOTA
struct dquot *i_dquot[MAXQUOTAS];
#endif
struct list_head i_devices;
/*說(shuō)明了三種不同的驅(qū)動(dòng)類型*/
union {
struct pipe_inode_info *i_pipe;
struct block_device *i_bdev;
struct cdev *i_cdev;
};
__u32 i_generation;
#ifdef CONFIG_FSNOTIFY
__u32 i_fsnotify_mask; /* all events this inode cares about */
struct hlist_head i_fsnotify_marks;
#endif
#ifdef CONFIG_IMA
/* protected by i_lock */
unsigned int i_readcount; /* struct files open RO */
#endif
/*寫(xiě)者使用次數(shù)*/
atomic_t i_writecount;
#ifdef CONFIG_SECURITY
void *i_security;
#endif
#ifdef CONFIG_FS_POSIX_ACL
struct posix_acl *i_acl;
struct posix_acl *i_default_acl;
#endif
void *i_private; /* fs or device private pointer */
};
驅(qū)動(dòng)程序設(shè)計(jì)過(guò)程中通常采用i_rdev判斷設(shè)備文件的設(shè)備號(hào)。
struct file是指文件對(duì)象，表示進(jìn)程中打開(kāi)的文件，一個(gè)物理文件只有一個(gè)inode,但是可以被打開(kāi)很多次，因此可以存在很多struct file結(jié)構(gòu)體。
struct file {
/*
* fu_list becomes invalid after file_free is called and queued via
* fu_rcuhead for RCU freeing
*/
union {
struct list_head fu_list;
struct rcu_head fu_rcuhead;
} f_u;
/*文件的路徑*/
struct path f_path;
#define f_dentry f_path.dentry
#define f_vfsmnt f_path.mnt
/*該文件支持的操作集合*/
const struct file_operations *f_op;
spinlock_t f_lock; /* f_ep_links, f_flags, no IRQ */
#ifdef CONFIG_SMP
int f_sb_list_cpu;
#endif
/*文件對(duì)象的使用次數(shù)*/
atomic_long_t f_count;
unsigned int f_flags;
fmode_t f_mode;
loff_t f_pos;
struct fown_struct f_owner;
const struct cred *f_cred;
struct file_ra_state f_ra;
u64 f_version;
#ifdef CONFIG_SECURITY
void *f_security;
#endif
/* needed for tty driver, and maybe others */
/*通常用來(lái)指向具體的數(shù)據(jù)或者設(shè)備文件，實(shí)現(xiàn)操作*/
void *private_data;
#ifdef CONFIG_EPOLL
/* Used by fs/eventpoll.c to link all the hooks to this file */
struct list_head f_ep_links;
#endif /* #ifdef CONFIG_EPOLL */
struct address_space *f_mapping;
#ifdef CONFIG_DEBUG_WRITECOUNT
unsigned long f_mnt_write_state;
#endif
};
訪問(wèn)inode主要是通過(guò)這兩個(gè)機(jī)構(gòu)體之間的管理型。
struct path {
struct vfsmount *mnt;
struct dentry *dentry;
};
struct dentry {
/* RCU lookup touched fields */
unsigned int d_flags; /* protected by d_lock */
seqcount_t d_seq; /* per dentry seqlock */
struct hlist_bl_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name;
struct inode *d_inode; /* Where the name belongs to - NULL is
* negative */
unsigned char d_iname[DNAME_INLINE_LEN]; /* small names */
/* Ref lookup also touches following */
unsigned int d_count; /* protected by d_lock */
spinlock_t d_lock; /* per dentry lock */
const struct dentry_operations *d_op;
struct super_block *d_sb; /* The root of the dentry tree */
unsigned long d_time; /* used by d_revalidate */
void *d_fsdata; /* fs-specific data */
struct list_head d_lru; /* LRU list */
/*
* d_child and d_rcu can share memory
*/
union {
struct list_head d_child; /* child of parent list */
struct rcu_head d_rcu;
} d_u;
struct list_head d_subdirs; /* our children */
struct list_head d_alias; /* inode alias list */
};
其中的可以通過(guò)struct file間接的訪問(wèn)物理文件的struct inode,具體的實(shí)現(xiàn)是filp->f_path.entry->d_inode,這個(gè)過(guò)程也就實(shí)現(xiàn)了將inode和file結(jié)構(gòu)體之間的聯(lián)系。
上面的幾個(gè)主要的結(jié)構(gòu)體是驅(qū)動(dòng)實(shí)現(xiàn)過(guò)程中最重要的幾個(gè)。具體的意義還要聯(lián)系起來(lái)分析。