fs/nsfs.c

   1 #include <linux/mount.h>
   2 #include <linux/file.h>
   3 #include <linux/fs.h>
   4 #include <linux/proc_ns.h>
   5 #include <linux/magic.h>
   6 #include <linux/ktime.h>
   7 #include <linux/seq_file.h>
   8
   9 static struct vfsmount *nsfs_mnt;
  10
  11 static const struct file_operations ns_file_operations = {
  12         .llseek         = no_llseek,
  13 };
  14
  15 static char *ns_dname(struct dentry *dentry, char *buffer, int buflen)
  16 {
  17         struct inode *inode = d_inode(dentry);
  18         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
  19
  20         return dynamic_dname(dentry, buffer, buflen, "%s:[%lu]",
  21                 ns_ops->name, inode->i_ino);
  22 }
  23
  24 static void ns_prune_dentry(struct dentry *dentry)
  25 {
  26         struct inode *inode = d_inode(dentry);
  27         if (inode) {
  28                 struct ns_common *ns = inode->i_private;
  29                 atomic_long_set(&ns->stashed, 0);
  30         }
  31 }
  32
  33 const struct dentry_operations ns_dentry_operations =
  34 {
  35         .d_prune        = ns_prune_dentry,
  36         .d_delete       = always_delete_dentry,
  37         .d_dname        = ns_dname,
  38 };
  39
  40 static void nsfs_evict(struct inode *inode)
  41 {
  42         struct ns_common *ns = inode->i_private;
  43         clear_inode(inode);
  44         ns->ops->put(ns);
  45 }
  46
  47 void *ns_get_path(struct path *path, struct task_struct *task,
  48                         const struct proc_ns_operations *ns_ops)
  49 {
  50         struct vfsmount *mnt = mntget(nsfs_mnt);
  51         struct qstr qname = { .name = "", };
  52         struct dentry *dentry;
  53         struct inode *inode;
  54         struct ns_common *ns;
  55         unsigned long d;
  56
  57 again:
  58         ns = ns_ops->get(task);
  59         if (!ns) {
  60                 mntput(mnt);
  61                 return ERR_PTR(-ENOENT);
  62         }
  63         rcu_read_lock();
  64         d = atomic_long_read(&ns->stashed);
  65         if (!d)
  66                 goto slow;
  67         dentry = (struct dentry *)d;
  68         if (!lockref_get_not_dead(&dentry->d_lockref))
  69                 goto slow;
  70         rcu_read_unlock();
  71         ns_ops->put(ns);
  72 got_it:
  73         path->mnt = mnt;
  74         path->dentry = dentry;
  75         return NULL;
  76 slow:
  77         rcu_read_unlock();
  78         inode = new_inode_pseudo(mnt->mnt_sb);
  79         if (!inode) {
  80                 ns_ops->put(ns);
  81                 mntput(mnt);
  82                 return ERR_PTR(-ENOMEM);
  83         }
  84         inode->i_ino = ns->inum;
  85         inode->i_mtime = inode->i_atime = inode->i_ctime = CURRENT_TIME;
  86         inode->i_flags |= S_IMMUTABLE;
  87         inode->i_mode = S_IFREG | S_IRUGO;
  88         inode->i_fop = &ns_file_operations;
  89         inode->i_private = ns;
  90
  91         dentry = d_alloc_pseudo(mnt->mnt_sb, &qname);
  92         if (!dentry) {
  93                 iput(inode);
  94                 mntput(mnt);
  95                 return ERR_PTR(-ENOMEM);
  96         }
  97         d_instantiate(dentry, inode);
  98         dentry->d_fsdata = (void *)ns_ops;
  99         d = atomic_long_cmpxchg(&ns->stashed, 0, (unsigned long)dentry);
 100         if (d) {
 101                 d_delete(dentry);       /* make sure ->d_prune() does nothing */
 102                 dput(dentry);
 103                 cpu_relax();
 104                 goto again;
 105         }
 106         goto got_it;
 107 }
 108
 109 int ns_get_name(char *buf, size_t size, struct task_struct *task,
 110                         const struct proc_ns_operations *ns_ops)
 111 {
 112         struct ns_common *ns;
 113         int res = -ENOENT;
 114         ns = ns_ops->get(task);
 115         if (ns) {
 116                 res = snprintf(buf, size, "%s:[%u]", ns_ops->name, ns->inum);
 117                 ns_ops->put(ns);
 118         }
 119         return res;
 120 }
 121
 122 struct file *proc_ns_fget(int fd)
 123 {
 124         struct file *file;
 125
 126         file = fget(fd);
 127         if (!file)
 128                 return ERR_PTR(-EBADF);
 129
 130         if (file->f_op != &ns_file_operations)
 131                 goto out_invalid;
 132
 133         return file;
 134
 135 out_invalid:
 136         fput(file);
 137         return ERR_PTR(-EINVAL);
 138 }
 139
 140 static int nsfs_show_path(struct seq_file *seq, struct dentry *dentry)
 141 {
 142         struct inode *inode = d_inode(dentry);
 143         const struct proc_ns_operations *ns_ops = dentry->d_fsdata;
 144
 145         seq_printf(seq, "%s:[%lu]", ns_ops->name, inode->i_ino);
 146         return 0;
 147 }
 148
 149 static const struct super_operations nsfs_ops = {
 150         .statfs = simple_statfs,
 151         .evict_inode = nsfs_evict,
 152         .show_path = nsfs_show_path,
 153 };
 154 static struct dentry *nsfs_mount(struct file_system_type *fs_type,
 155                         int flags, const char *dev_name, void *data)
 156 {
 157         return mount_pseudo(fs_type, "nsfs:", &nsfs_ops,
 158                         &ns_dentry_operations, NSFS_MAGIC);
 159 }
 160 static struct file_system_type nsfs = {
 161         .name = "nsfs",
 162         .mount = nsfs_mount,
 163         .kill_sb = kill_anon_super,
 164 };
 165
 166 void __init nsfs_init(void)
 167 {
 168         nsfs_mnt = kern_mount(&nsfs);
 169         if (IS_ERR(nsfs_mnt))
 170                 panic("can't set nsfs up\n");
 171         nsfs_mnt->mnt_sb->s_flags &= ~MS_NOUSER;
 172 }