Hi michi and peter, Nice discussion. On Fri, Apr 3, 2009 at 10:09 PM, Michael Blizek <michi1@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx> wrote: > Hi! > > On 14:45 Fri 03 Apr , Peter Teoh wrote: >> Er....yes, i understand what u are saying.....but then I am lost over >> your original question. >> >> Can you re-explain your original question again? Now I don't quite understand. > > Devesh wanted to do trylock of a semaphore inside a workqueue and return > ERESTARTSYS if locking fails. There are some things which are wrong with > this approach. > > 1) Mutexes should be prefered over semaphores, if possible. If it is not > possible, it might be a case which is not well suited for a workqueue. e.g. > you can create a request queue and use a semaphore for counting the number of > requests in the queue and sleeping if there are no requests until one arrives. > > 2) I have never used trylock and I still do not know what he wants to do with > it. I am just trying to understand trylock APIs and analysing the differences b/w the _interruptible and trylock.. > > 3) ERESTARTSYS is for use with the _interruptable functions of mutex_lock > and others. It makes only sense inside system calls, because its purpose is > to exit the system call prematurely in order to let a signal be delivered to > the user space process. The system call will then fail with errno set to > EINTR. > 3.1) Returning ERESTARTSYS in a workqueue will not not work. The workqueue > function has to return void, so the return code will get lost. > 3.2) Returning ERESTARTSYS is only valid for the _interruptable functions if > a signal is pending. Returning it after trylock if something is currently > locked will not work (why would you want to do this anyway?). Ohh......its this way!! I was in an impression that...if ERESTARTSYS is returned, _anyhow_ (I mean independent of _interruptible or trylock), the execution context (system call) will restart. That is why I was thinking, that one can return ERESTARTSYS even with trylock..:( Are you saying that using ERESTARTSYS is worthless with trylock? Can you clarify "Is only valid for the _interruptable" if its returned even with trylock then will functioning of ERESTARTSYS will be droped? or its inherent prperty of implementation to by-pass the functioning? > > -Michi > -- > programing a layer 3+4 network protocol for mesh networks > see http://michaelblizek.twilightparadox.com > > -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
