On Mon, Feb 14, 2011 at 02:44:29PM -0600, Grant Edwards wrote: > Attached is a patch against 4.5.20 that adds two new command line > options: > > -y Attempt to display paths associated with file descriptor > arguments.
This feature looks promising, I'd like to have it implemented in strace. I'm not sure about option name; at least, the link between -y and its effect is not obvious to me. > -P <pathlist> > > Display only system calls accessing one of the paths in the > specified colon-separated path list. I think colon-separated path list is not quite convenient; from user point of view, I'd prefer to specify one path per option, like -p. > The features above depend on added code that attempts to track the > state of the traced process's fd table based on the observed > open/close/dup/clone system calls. Another approach would be to do a > readlink() on /proc/<pid>/fd/<fd> every time we handle a system call > with a file descriptor argument. I decided against the readlink() > approach in order to avoid the additional overhead and to provide a > workable solution on systems that don't have /proc/<pid>/fd links > available. The approach to track descriptors is much more complicated (and therefore more error-prone) and less reliable than readlink-based because of all details that have to be taken into account to trace descriptors properly. The overhead of readlink-based method is one syscall per descriptor, that's hardly noticeable compared to multiple syscalls strace already does to parse a single syscall made by the target process. > While the attached patch currently meets all of my requirements, there > are areas where it would need to be improved before it could be > merged into the repository: > > 1) Support for non-Linux OSes isn't done yet. For example, the > handling of the clone system call where it is determined whether > to copy or share the descriptor state assumes the OS is Linux. I wouldn't bother of non-Linux OSes. There are no feedback from these OSes at all, so lets place the feature under #ifdef LINUX and leave non-Linux case to people who care about strace on non-Linux. -- ldv
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