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 #include <linux/fs_struct.h>
   7
   8 /*
   9  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
  10  * It can block.
  11  */
  12 void set_fs_root(struct fs_struct *fs, struct path *path)
  13 {
  14         struct path old_root;
  15
  16         write_lock(&fs->lock);
  17         old_root = fs->root;
  18         fs->root = *path;
  19         path_get(path);
  20         write_unlock(&fs->lock);
  21         if (old_root.dentry)
  22                 path_put(&old_root);
  23 }
  24
  25 /*
  26  * Replace the fs->{pwdmnt,pwd} with {mnt,dentry}. Put the old values.
  27  * It can block.
  28  */
  29 void set_fs_pwd(struct fs_struct *fs, struct path *path)
  30 {
  31         struct path old_pwd;
  32
  33         write_lock(&fs->lock);
  34         old_pwd = fs->pwd;
  35         fs->pwd = *path;
  36         path_get(path);
  37         write_unlock(&fs->lock);
  38
  39         if (old_pwd.dentry)
  40                 path_put(&old_pwd);
  41 }
  42
  43 void chroot_fs_refs(struct path *old_root, struct path *new_root)
  44 {
  45         struct task_struct *g, *p;
  46         struct fs_struct *fs;
  47         int count = 0;
  48
  49         read_lock(&tasklist_lock);
  50         do_each_thread(g, p) {
  51                 task_lock(p);
  52                 fs = p->fs;
  53                 if (fs) {
  54                         write_lock(&fs->lock);
  55                         if (fs->root.dentry == old_root->dentry
  56                             && fs->root.mnt == old_root->mnt) {
  57                                 path_get(new_root);
  58                                 fs->root = *new_root;
  59                                 count++;
  60                         }
  61                         if (fs->pwd.dentry == old_root->dentry
  62                             && fs->pwd.mnt == old_root->mnt) {
  63                                 path_get(new_root);
  64                                 fs->pwd = *new_root;
  65                                 count++;
  66                         }
  67                         write_unlock(&fs->lock);
  68                 }
  69                 task_unlock(p);
  70         } while_each_thread(g, p);
  71         read_unlock(&tasklist_lock);
  72         while (count--)
  73                 path_put(old_root);
  74 }
  75
  76 void free_fs_struct(struct fs_struct *fs)
  77 {
  78         path_put(&fs->root);
  79         path_put(&fs->pwd);
  80         kmem_cache_free(fs_cachep, fs);
  81 }
  82
  83 void exit_fs(struct task_struct *tsk)
  84 {
  85         struct fs_struct *fs = tsk->fs;
  86
  87         if (fs) {
  88                 int kill;
  89                 task_lock(tsk);
  90                 write_lock(&fs->lock);
  91                 tsk->fs = NULL;
  92                 kill = !--fs->users;
  93                 write_unlock(&fs->lock);
  94                 task_unlock(tsk);
  95                 if (kill)
  96                         free_fs_struct(fs);
  97         }
  98 }
  99
 100 struct fs_struct *copy_fs_struct(struct fs_struct *old)
 101 {
 102         struct fs_struct *fs = kmem_cache_alloc(fs_cachep, GFP_KERNEL);
 103         /* We don't need to lock fs - think why ;-) */
 104         if (fs) {
 105                 fs->users = 1;
 106                 fs->in_exec = 0;
 107                 rwlock_init(&fs->lock);
 108                 fs->umask = old->umask;
 109                 read_lock(&old->lock);
 110                 fs->root = old->root;
 111                 path_get(&old->root);
 112                 fs->pwd = old->pwd;
 113                 path_get(&old->pwd);
 114                 read_unlock(&old->lock);
 115         }
 116         return fs;
 117 }
 118
 119 int unshare_fs_struct(void)
 120 {
 121         struct fs_struct *fs = current->fs;
 122         struct fs_struct *new_fs = copy_fs_struct(fs);
 123         int kill;
 124
 125         if (!new_fs)
 126                 return -ENOMEM;
 127
 128         task_lock(current);
 129         write_lock(&fs->lock);
 130         kill = !--fs->users;
 131         current->fs = new_fs;
 132         write_unlock(&fs->lock);
 133         task_unlock(current);
 134
 135         if (kill)
 136                 free_fs_struct(fs);
 137
 138         return 0;
 139 }
 140 EXPORT_SYMBOL_GPL(unshare_fs_struct);
 141
 142 int current_umask(void)
 143 {
 144         return current->fs->umask;
 145 }
 146 EXPORT_SYMBOL(current_umask);
 147
 148 /* to be mentioned only in INIT_TASK */
 149 struct fs_struct init_fs = {
 150         .users          = 1,
 151         .lock           = __RW_LOCK_UNLOCKED(init_fs.lock),
 152         .umask          = 0022,
 153 };
 154
 155 void daemonize_fs_struct(void)
 156 {
 157         struct fs_struct *fs = current->fs;
 158
 159         if (fs) {
 160                 int kill;
 161
 162                 task_lock(current);
 163
 164                 write_lock(&init_fs.lock);
 165                 init_fs.users++;
 166                 write_unlock(&init_fs.lock);
 167
 168                 write_lock(&fs->lock);
 169                 current->fs = &init_fs;
 170                 kill = !--fs->users;
 171                 write_unlock(&fs->lock);
 172
 173                 task_unlock(current);
 174                 if (kill)
 175                         free_fs_struct(fs);
 176         }
 177 }