On Tuesday 17 May 2005 02:09, Young Koh wrote: > Ok, now i'm getting close. Thanks a lot!!! > but i have two more :) > > 1) in SKAS mode, the tracer (UML kernel) will execute a system call > for the tracee (the user process). But what if the system call blocks? > then, the tracer, the UML kernel, will be blocked, too, right? it > means the whole UML system will be blocked? Good question. However the tracee is one of the threads running inside UML, i.e. switch_to_skas switches between the different tracees. However, that's done only on timer interrupts, and possibly those interrupts are blocked by the syscall execution.
Indeed, I remember that when the UBD I/O is run by the UML kernel and not by a separate thread (this has been removed) the whole system becomes *really* slow, so probably the answer to your question is "Yes, but UML tries to avoid this". > 2) in TT mode, what if the user process (tracee) installs its own > signal handler for SIGUSR2? The syscall is intercepted so it can't install signal handlers; the one it installs are handled inside the UML kernel. -- Paolo Giarrusso, aka Blaisorblade Skype user "PaoloGiarrusso" Linux registered user n. 292729 http://www.user-mode-linux.org/~blaisorblade ------------------------------------------------------- This SF.Net email is sponsored by Oracle Space Sweepstakes Want to be the first software developer in space? Enter now for the Oracle Space Sweepstakes! http://ads.osdn.com/?ad_id=7412&alloc_id=16344&op=click _______________________________________________ User-mode-linux-devel mailing list User-mode-linux-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/user-mode-linux-devel
