The lines
    if(ip-type != T_DIR){
      iunlockput(ip);
      return 0;
    }
in namex() function
mean

Question

The lines 
     if(ip->type != T_DIR){ 
       iunlockput(ip); 
       return 0; 
     } 
 in namex() function 
 mean

Answer

No directory entry was found for the file to be opened, hence an error

Answer

ilock is held on the inode, and hence it's an error if it is a directory

Answer

One of the sub-components on the given path name, was not a directory, hence it's an error

Answer

The last path component (which is a file, and not a directory) has been resolved, so release the lock (using iunlockput) and return

Answer

There was a syntax error in the pathname specified

Answer

One of the sub-components on the given path name, was a directory, but it was not supposed to be a directory, hence an error

Answer

One of the sub-components on the given path name, did not exist, hence it's an error

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