root/fs/proc/link.c

/* */

DEFINITIONS

1. proc_follow_link
2. proc_readlink

   1 /*
   2  *  linux/fs/proc/link.c
   3  *
   4  *  Copyright (C) 1991, 1992  Linus Torvalds
   5  *
   6  *  /proc link-file handling code
   7  */
   8 
   9 #include <asm/segment.h>
  10 
  11 #include <linux/errno.h>
  12 #include <linux/sched.h>
  13 #include <linux/fs.h>
  14 #include <linux/mm.h>
  15 #include <linux/proc_fs.h>
  16 #include <linux/stat.h>
  17 
  18 static int proc_readlink(struct inode *, char *, int);
  19 static int proc_follow_link(struct inode *, struct inode *, int, int,
  20                             struct inode **);
  21 
  22 /*
  23  * PLAN9_SEMANTICS won't work any more: it used an ugly hack that broke 
  24  * when the files[] array was updated only after the open code
  25  */
  26 #undef PLAN9_SEMANTICS
  27 
  28 /*
  29  * links can't do much...
  30  */
  31 static struct file_operations proc_fd_link_operations = {
  32         NULL,                   /* lseek - default */
  33         NULL,                   /* read - bad */
  34         NULL,                   /* write - bad */
  35         NULL,                   /* readdir - bad */
  36         NULL,                   /* select - default */
  37         NULL,                   /* ioctl - default */
  38         NULL,                   /* mmap */
  39         NULL,                   /* very special open code */
  40         NULL,                   /* no special release code */
  41         NULL                    /* can't fsync */
  42 };
  43 
  44 struct inode_operations proc_link_inode_operations = {
  45         &proc_fd_link_operations,/* file-operations */
  46         NULL,                   /* create */
  47         NULL,                   /* lookup */
  48         NULL,                   /* link */
  49         NULL,                   /* unlink */
  50         NULL,                   /* symlink */
  51         NULL,                   /* mkdir */
  52         NULL,                   /* rmdir */
  53         NULL,                   /* mknod */
  54         NULL,                   /* rename */
  55         proc_readlink,          /* readlink */
  56         proc_follow_link,       /* follow_link */
  57         NULL,                   /* bmap */
  58         NULL,                   /* truncate */
  59         NULL                    /* permission */
  60 };
  61 
  62 
  63 static int proc_follow_link(struct inode * dir, struct inode * inode,
     /*  */
  64         int flag, int mode, struct inode ** res_inode)
  65 {
  66         unsigned int pid, ino;
  67         struct task_struct * p;
  68         struct inode * new_inode;
  69         int i, error;
  70 
  71         *res_inode = NULL;
  72         if (dir)
  73                 iput(dir);
  74         if (!inode)
  75                 return -ENOENT;
  76         if ((error = permission(inode, MAY_EXEC)) != 0){
  77                 iput(inode);
  78                 return error;
  79         }
  80         ino = inode->i_ino;
  81         pid = ino >> 16;
  82         ino &= 0x0000ffff;
  83         for (i = 0 ; i < NR_TASKS ; i++)
  84                 if ((p = task[i]) && p->pid == pid)
  85                         break;
  86         if (i >= NR_TASKS) {
  87                 iput(inode);
  88                 return -ENOENT;
  89         }
  90         new_inode = NULL;
  91         switch (ino) {
  92                 case PROC_PID_CWD:
  93                         if (!p->fs)
  94                                 break;
  95                         new_inode = p->fs->pwd;
  96                         break;
  97                 case PROC_PID_ROOT:
  98                         if (!p->fs)
  99                                 break;
 100                         new_inode = p->fs->root;
 101                         break;
 102                 case PROC_PID_EXE: {
 103                         struct vm_area_struct * vma;
 104                         if (!p->mm)
 105                                 break;
 106                         vma = p->mm->mmap;
 107                         while (vma) {
 108                                 if (vma->vm_flags & VM_EXECUTABLE) {
 109                                         new_inode = vma->vm_inode;
 110                                         break;
 111                                 }
 112                                 vma = vma->vm_next;
 113                         }
 114                         break;
 115                 }
 116                 default:
 117                         switch (ino >> 8) {
 118                         case PROC_PID_FD_DIR:
 119                                 if (!p->files)
 120                                         break;
 121                                 ino &= 0xff;
 122                                 if (ino < NR_OPEN && p->files->fd[ino]) {
 123                                         new_inode = p->files->fd[ino]->f_inode;
 124                                 }
 125                                 break;
 126                         }
 127         }
 128         iput(inode);
 129         if (!new_inode)
 130                 return -ENOENT;
 131         *res_inode = new_inode;
 132         new_inode->i_count++;
 133         return 0;
 134 }
 135 
 136 static int proc_readlink(struct inode * inode, char * buffer, int buflen)
     /*  */
 137 {
 138         int i;
 139         unsigned int dev,ino;
 140         char buf[64];
 141 
 142         if (!S_ISLNK(inode->i_mode)) {
 143                 iput(inode);
 144                 return -EINVAL;
 145         }
 146         i = proc_follow_link(NULL, inode, 0, 0, &inode);
 147         if (i)
 148                 return i;
 149         if (!inode)
 150                 return -EIO;
 151         dev = kdev_t_to_nr(inode->i_dev);
 152         ino = inode->i_ino;
 153         iput(inode);
 154         i = sprintf(buf,"[%04x]:%u", dev, ino);
 155         if (buflen > i)
 156                 buflen = i;
 157         i = 0;
 158         while (i < buflen)
 159                 put_user(buf[i++],buffer++);
 160         return i;
 161 }

/* */