一. 情景模式
1. 获取文件的绝对路径，这里指由fd获取
2. 获取进程的绝对路径
二. linux kernel 和路径有关的2个数据结构：
1. struct dentry 文件名保存在这个结构体
结构体原型：
struct dentry {
int d_mounted;
struct inode *d_inode;/* Where the name belongs to - NULL is negative */
struct hlist_node d_hash; /* lookup hash list */
struct dentry *d_parent; /* parent directory */
struct qstr d_name; /* 文件名在这里 */
/* 省略若干内容 */
};
2. struct vfsmount 文件系统的挂载信息，mount 命令
结构体原型：
struct vfsmount {
struct list_head mnt_hash;
struct vfsmount *mnt_parent; /* fs we are mounted on */
struct dentry *mnt_mountpoint; /* dentry of mountpoint */
struct dentry *mnt_root; /* root of the mounted tree */
/* 省略若干内容 */
};
三. 从struct dentry 和struct vfsmount 回溯直到/ ，即可拼凑出完整路径
获取进程绝对路径例子一个：
void get_absolute_path()
{
/* 假设 512 已经足够了 */
char * tmp_path[512];
char * ptr = NULL;
struct dentry *dentry = NULL;
struct vfsmount * mnt = NULL;
memset(tmp_path,'\0',512);
ptr = tmp_path + 512 -1;
task_lock(current);
/* Get the Process working dentry */
dentry = current->fs->pwd.dentry;
/* Get the Process working vfsmount */
mnt = current->fs->pwd.mnt;
do
{
/* Process the dentry */
while(dentry && dentry->d_name.name && strcmp(dentry->d_name.name,"/"))
{
ptr = ptr - strlen(dentry->d_name.name);
if(ptr <= tmp_path + strlen(dentry->d_name.name) + 1)
{
break;
}
memcpy(ptr,dentry->d_name.name,strlen(dentry->d_name.name));
*(--ptr) = '/';
dentry= dentry->d_parent;
}
/* Process the filesystem mountpoint, 突破挂载点 */
if(mnt && mnt->mnt_mountpoint\
&& mnt->mnt_mountpoint->d_name.name\
&& strcmp(mnt->mnt_mountpoint->d_name.name,"/"))
{
dentry = mnt->mnt_mountpoint;
ptr = ptr - strlen(dentry->d_name.name);
if(ptr <= tmp_path + strlen(dentry->d_name.name) + 1)
{
break;
}
memcpy(ptr,dentry->d_name.name,strlen(dentry->d_name.name));
*(--ptr) = '/';
mnt = mnt->mnt_parent;
dentry= dentry->d_parent;
}
}while( 0 != strcmp(mnt->mnt_mountpoint->d_name.name,"/")); /* end do */
/* 直到文件系统的挂载点为 / */
task_unlock(current);
printk("full path: %s\n",ptr);
}
由于自己实现，考虑不周，当遇到目录挂载目录（mount --rbind）时，处理可能会出问题。
更好的方法且见下回分解