fs/fs_struct.c

   1 #include <linux/module.h>
   2 #include <linux/sched.h>
   3 #include <linux/fs.h>
   4 #include <linux/path.h>
   5 #include <linux/slab.h>
   6
   7 /*
   8  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
   9  * It can block.
  10  */
  11 void set_fs_root(struct fs_struct *fs, struct path *path)
  12 {
  13         struct path old_root;
  14
  15         write_lock(&fs->lock);
  16         old_root = fs->root;
  17         fs->root = *path;
  18         path_get(path);
  19         write_unlock(&fs->lock);
  20         if (old_root.dentry)
  21                 path_put(&old_root);
  22 }
  23
  24 /*
  25  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
  26  * It can block.
  27  */
  28 void set_fs_pwd(struct fs_struct *fs, struct path *path)
  29 {
  30         struct path old_pwd;
  31
  32         write_lock(&fs->lock);
  33         old_pwd = fs->pwd;
  34         fs->pwd = *path;
  35         path_get(path);
  36         write_unlock(&fs->lock);
  37
  38         if (old_pwd.dentry)
  39                 path_put(&old_pwd);
  40 }
  41
  42 void chroot_fs_refs(struct path *old_root, struct path *new_root)
  43 {
  44         struct task_struct *g, *p;
  45         struct fs_struct *fs;
  46         int count = 0;
  47
  48         read_lock(&tasklist_lock);
  49         do_each_thread(g, p) {
  50                 task_lock(p);
  51                 fs = p->fs;
  52                 if (fs) {
  53                         write_lock(&fs->lock);
  54                         if (fs->root.dentry == old_root->dentry
  55                             && fs->root.mnt == old_root->mnt) {
  56                                 path_get(new_root);
  57                                 fs->root = *new_root;
  58                                 count++;
  59                         }
  60                         if (fs->pwd.dentry == old_root->dentry
  61                             && fs->pwd.mnt == old_root->mnt) {
  62                                 path_get(new_root);
  63                                 fs->pwd = *new_root;
  64                                 count++;
  65                         }
  66                         write_unlock(&fs->lock);
  67                 }
  68                 task_unlock(p);
  69         } while_each_thread(g, p);
  70         read_unlock(&tasklist_lock);
  71         while (count--)
  72                 path_put(old_root);
  73 }
  74
  75 void put_fs_struct(struct fs_struct *fs)
  76 {
  77         /* No need to hold fs->lock if we are killing it */
  78         if (atomic_dec_and_test(&fs->count)) {
  79                 path_put(&fs->root);
  80                 path_put(&fs->pwd);
  81                 kmem_cache_free(fs_cachep, fs);
  82         }
  83 }
  84
  85 void exit_fs(struct task_struct *tsk)
  86 {
  87         struct fs_struct * fs = tsk->fs;
  88
  89         if (fs) {
  90                 task_lock(tsk);
  91                 tsk->fs = NULL;
  92                 task_unlock(tsk);
  93                 put_fs_struct(fs);
  94         }
  95 }
  96
  97 struct fs_struct *copy_fs_struct(struct fs_struct *old)
  98 {
  99         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
 100         /* We don't need to lock fs - think why ;-) */
 101         if (fs) {
 102                 atomic_set(&fs->count, 1);
 103                 rwlock_init(&fs->lock);
 104                 fs->umask = old->umask;
 105                 read_lock(&old->lock);
 106                 fs->root = old->root;
 107                 path_get(&old->root);
 108                 fs->pwd = old->pwd;
 109                 path_get(&old->pwd);
 110                 read_unlock(&old->lock);
 111         }
 112         return fs;
 113 }
 114
 115 int unshare_fs_struct(void)
 116 {
 117         struct fs_struct *fsp = copy_fs_struct(current->fs);
 118         if (!fsp)
 119                 return -ENOMEM;
 120         exit_fs(current);
 121         current->fs = fsp;
 122         return 0;
 123 }
 124 EXPORT_SYMBOL_GPL(unshare_fs_struct);
 125
 126 /* to be mentioned only in INIT_TASK */
 127 struct fs_struct init_fs = {
 128         .count          = ATOMIC_INIT(1),
 129         .lock           = __RW_LOCK_UNLOCKED(init_fs.lock),
 130         .umask          = 0022,
 131 };
 132
 133 void daemonize_fs_struct(void)
 134 {
 135         struct fs_struct *fs;
 136
 137         exit_fs(current);       /* current->fs->count--; */
 138         fs = &init_fs;
 139         current->fs = fs;
 140         atomic_inc(&fs->count);
 141 }