Linux kernel 絕對路徑之自己實現篇

一. 情景模式1.  擷取檔案的絕對路徑，這裡指由fd擷取2.  擷取進程的絕對路徑二. linux kernel 和路徑有關的2個資料結構：1. struct dentry 檔案名稱儲存在這個結構體結構體原型：

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;         /* 檔案名稱在這裡 */    /* 省略若干內容 */};

2. struct vfsmount 檔案系統的掛載資訊，mount 命令結構體原型：

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 */    /* 省略若干內容 */};

三. 從struct dentry 和struct vfsmount 回溯直到/ ，即可拼湊出完整路徑擷取進程絕對路徑例子一個：

void get_absolute_path(){    /* 假設 512 已經足夠了 */    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, 突破掛載點 */        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 */    /* 直到檔案系統的掛載點為 / */    task_unlock(current);    printk("full path: %s\n",ptr);}

由於自己實現，考慮不周，當遇到目錄掛載目錄（mount --rbind）時，處理可能會出問題。更好的方法且見下回分解