管道在linux的实现

//定义一个文件系统的类型
static DECLARE_FSTYPE(pipe_fs_type,"pipefs",pipefs_read_super,FS_NOMOUNT);

//管道超级块
static struct super_block *pipefs_read_super(struct super_block *sb,void *data,int silent)
{
    struct inode *root=new inode(sb);                     //生成管道文件系统的根目录的内存inode

    if(!root)
        return NULL;
    root->imode=S_IFDIR|S_IRUSR|S_IWUSR;
    root->i_uid=root->i_gid=0;
    root->i_atime=root->mtime=root->i_ctime=CURRENT_TIME;
    sb->s_blocksize=1024;
    sb->s_blocksize_bits=10;
    sb->s_magic=PIPEFS_MAGIC;
    sb->s_op=&pipefs_ops;                                   //设置超级块sb的s_ob域的值为pipefs_ops结构的指针。
    sb->s_root=d_alloc(NULL,&(const struct qstr) {"pipe:",5,0});  //设置超级块的s_root域，s_root域的类型是struct dentry*,指向根目录的对象
    if(!sb->s_root)
    {
        iput(root);
        return NULL;
    }
    sb->s_root->d_sb=sb;
    sb->s_root->d_parent=sb->s_root;    //将刚分配的目录项对象与前面生成的根目录inode连接起来
    d_instantiate(sb->s_root,root);
    return sb;
}

static struct super_operations pipefs_ops=
{
statfs:pipefs_statfs,
};

struct pipe_inode_info
{
    wait_queue_head_t wait;            //管道等待队列指针wait    
    char *base;                        //内核缓冲区基地址base
    unsigned int len;
    unsigned int start;
    unsigned int readers;
    unsigned int writers;
    unsigned int waiting_readers;
    unsigned int waiting_writers;
    unsigned int r_counter;
    unsigned int w_counter;
};


#define PIPE_SIZE PAGE_SIZE

#define PIPE_SEM(inode)  (&(inode).i_sem)
#define PIPE_WAIT(inode) (&(inode).i_pipe->wait)
#define PIPE_BASE(inode) (&(inode).i_pipe->base)
#define PIPE_START(inode) (&(inode).i_pipe->start)
#define PIPE_LEN(inode) (&(inode).i_pipe->len)
#define PIPE_READERS(inode) (&(inode).i_pipe->readers)
#define PIPE_WRITERS(inode) (&(inode).i_pipe->writers)
#define PIPE_WAITINT_READERS(inode) (&(inode).i_pipe->waiting_readers)
#define PIPE_WAITINT_WRITERS(inode) (&(inode).i_pipe->waitint_writers)
#define PIPE_RCOUNTER(inode) (&(inode).i_pipe->r_counter)
#define PIPE_WCOUNTER(inode) (&(inode).i_pipe->w_counter)

#define PIPE_EMPTY(inode) (PIPE_LEN(inode)==0)
#define PIPE_FULL(inode) (PIPE_LEN(inode)==PIPE_SIZE)
#define PIPE_FREE(inode) (PIPE_SIZE-PIPE_LEN(inode))
#define PIPE_END(inode) ((PIPE_START(inode)+PIPE_LEN(inode))&(PIPE_SIZE-1))
#define PIPE_MAX_RCHUNK(inode) (PIPE_SIZE-PIPE_START(inode))
#define PIPE_MAX_WCHUNK(inode) (PIPE_SIZE-PIPE_PIPE_END(inode))

#define PIPE_BUF 4096

struct file_operations read_pipe_fops={
       llseek:pipe_lseek,
       read:pipe_read,
       write:bad_pipe_w,
       poll:pipe_poll,
       ioctl:pipe_ioctl,
       open:pipe_open,
       release:pipe_read_release,
};


//管道的建立与释放
int do_pipe(int *fd)
{
    struct qstr this;
    char name[32];
    struct dentry *dentry;
    struct inode *inode;
    struct file *f1,*f2;
    int error;
    int i,j;

    error=-ENFILE;
    f1=get_empty_filp();
    if(!f1)
        goto no_files;

    f2=get_empty_filp();
    if(!f2)
        goto close_f1;

    inode=get_pipe_node();
    if(!inode)
        goto close_f12;
    
    error=get_unused_fd();
    if(error<0)
        goto close_f12_inode;
    i=error;

    error=get_unused_fd();
    if(error<0)
        goto close_f12_inode_i;
    j=error;

    error=-ENOMEM;
    sprintf(name,"[%lu]",inode->i_ino);
    this.name=name;
    this.len=strlen(name);
    this.hash=inode->i_ino;
    dentry=d_alloc(pipe_mnt->mnt_sb->s_root,&this); //生成一个目录项对象dentry，并通过它将上述两个文件对象与管道索引节点联系起来
    if(!dentry)
    {
        goto close_f12_inode_i_j;
    }
    dentry->d_op=&pipefs_dentry_operations;
    d_add(dentry,inode);
    f1->f_vfsmnt=f2->f_vfsmnt=mntget(mntget(pipe_mnt));
    f2->f_dentry=f1->f_dentry=dget(dentry);

    f1->f_pos=f2->pos=0;
    f1->f_flags=O_RDONLY;
    f1->f_op=&read_pipe_fops;
    f1->f_mode=1;
    f1->f_version=0;

    f2->f_flags=O_WRONLY;
    f2->f_op=&write_pipe_fops;
    f2->f_mode=2;
    f2->f_version=0;

    fd_install(i,f1);           //将两个文件对象与上述两个文件描述符联系起来
    fd_install(j,f2);
    fd[0]=i;
    fd[1]=j;
    return 0;

close_f12_inode_i_j:
    put_unused_fd(j);
close_f12_inode_i:
    put_unused_fd(i);
close_f12_inode:
    free_page((unsigned long)PIPE_BASE(*inode));
    kfree(inode->i_pipe);
    inode->i_pipe=NULL;
    iput(inode);
close_f12:
    put_filp(f2);
close_f1:
    put_filp(f1);
no_files:
    return error;
}