Messages in this thread | | | Date | Wed, 05 May 2004 13:50:03 +0200 | From | Bart Samwel <> | Subject | Re: Read from file fails |
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Libor Vanek wrote:
>>>>>OK - how can I "notify" userspace process? Signals are "weak" - I need >>>>>to send some data (filename etc.) to process. One solution is "on this >>>>>signal call this syscall and result of this syscall will be data you >>>>>need" - but I'd prefer to handle this in one "action". >>>> >>>>My first thoughts are to make it a blocking call. >>> >>>You mean like: >>>- send signal to user-space process >>>- wait until user-space process pick ups data (filename etc.), creates >>>copy of file (or whatever) and calls another system call that he's finished >>>- let kernel to continue syscall I blocked >>>? >> >>No, more like: >>- user-space process calls syscall, which blocks. >>- kernel captures a file write event, puts the info in some kind of >>queue, wakes up the user-space process and then waits for some kind of >>acknowledgement to be returned so that it may continue. >>- user-space process wakes up, the syscall completes, and passes a >>filename etc. to user-space. Copies the file, and calls a syscall to >>signify "hey, I'm done with that file". This syscall wakes up the kernel >>stuff that was waiting for this acknowledgement. >>- file write event continues >>- repeat from start > > OK - I'm thinking of using semaphores to "block" system call - is there something why this is not a good idea?
Semaphores are useful to protect a shared resource (and you might want to use those to protect your queue of filenames to copy), but not for transferring control between threads. I think you might want to look at wait_queue, wait_event, wake_up and things like that.
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