Path init

http://lxr.free-electrons.com/source/fs/namei.c#L1808

1808 static int path_init(int dfd, const char *name, unsigned int flags,
1809                      struct nameidata *nd, struct file **fp)
1810 {
1811         int retval = 0;
1812 
1813         nd->last_type = LAST_ROOT; /* if there are only slashes... */
1814         nd->flags = flags | LOOKUP_JUMPED;
1815         nd->depth = 0;
1816         if (flags & LOOKUP_ROOT) {
1817                 struct dentry *root = nd->root.dentry;
1818                 struct inode *inode = root->d_inode;
1819                 if (*name) {
1820                         if (!d_is_directory(root))
1821                                 return -ENOTDIR;
1822                         retval = inode_permission(inode, MAY_EXEC);
1823                         if (retval)
1824                                 return retval;
1825                 }
1826                 nd->path = nd->root;
1827                 nd->inode = inode;
1828                 if (flags & LOOKUP_RCU) {
1829                         rcu_read_lock();
1830                         nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
1831                         nd->m_seq = read_seqbegin(&mount_lock);
1832                 } else {
1833                         path_get(&nd->path);
1834                 }
1835                 return 0;
1836         }
1837 
1838         nd->root.mnt = NULL;
1839 
1840         nd->m_seq = read_seqbegin(&mount_lock);
1841         if (*name=='/') {
1842                 if (flags & LOOKUP_RCU) {
1843                         rcu_read_lock();
1844                         set_root_rcu(nd);
1845                 } else {
1846                         set_root(nd);
1847                         path_get(&nd->root);
1848                 }
1849                 nd->path = nd->root;
1850         } else if (dfd == AT_FDCWD) {
1851                 if (flags & LOOKUP_RCU) {
1852                         struct fs_struct *fs = current->fs;
1853                         unsigned seq;
1854 
1855                         rcu_read_lock();
1856 
1857                         do {
1858                                 seq = read_seqcount_begin(&fs->seq);
1859                                 nd->path = fs->pwd;
1860                                 nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
1861                         } while (read_seqcount_retry(&fs->seq, seq));
1862                 } else {
1863                         get_fs_pwd(current->fs, &nd->path);
1864                 }
1865         } else {
1866                 /* Caller must check execute permissions on the starting path component */
1867                 struct fd f = fdget_raw(dfd);
1868                 struct dentry *dentry;
1869 
1870                 if (!f.file)
1871                         return -EBADF;
1872 
1873                 dentry = f.file->f_path.dentry;
1874 
1875                 if (*name) {
1876                         if (!d_is_directory(dentry)) {
1877                                 fdput(f);
1878                                 return -ENOTDIR;
1879                         }
1880                 }
1881 
1882                 nd->path = f.file->f_path;
1883                 if (flags & LOOKUP_RCU) {
1884                         if (f.flags & FDPUT_FPUT)
1885                                 *fp = f.file;
1886                         nd->seq = __read_seqcount_begin(&nd->path.dentry->d_seq);
1887                         rcu_read_lock();
1888                 } else {
1889                         path_get(&nd->path);
1890                         fdput(f);
1891                 }
1892         }
1893 
1894         nd->inode = nd->path.dentry->d_inode;
1895         return 0;
1896 }