On 8/2/06, Deepak Joshi <deepak_cins@xxxxxxxxxxx> wrote:
Hi all, In case of down_interruptible( ) i read following explination in understanding linux kernel. "It is widely used by device drivers since it allows processes that receive a signal while being blocked on a semaphore to give up the "down" operation. If the sleeping process is awakened by a signal before getting the needed resource, the function increments the count field of the semaphore and returns the value -EINTR. On the other hand, if down_interruptible( ) runs to normal completion and gets the resource, it returns 0. The device driver may thus abort the I/O operation when the return value is -EINTR." so what type of signals they are talking abt ??? and how it is implemented ?? plz explain it to me.
signal here are the signal delivered to user process like a signal to abort or interrupt etc. down_interruptible() puts the current process in TASK_INTERRUPTIBLE state and puts it on semaphore queue of waiting processes and finally calls schedule() functions to give up CPU to other process, by doing so current process sleeps till the time state is not changed to TASK_RUNNING. When a signal is delivered to some process and that process is in TASK_INTERRUPTIBLE state, kernel changes the state from TASK_INTERRUPTIBLE to TASK_RUNNING (making them a possible candidate for selection in next schedule() call). So by calling down_interruptible() we make sure that the current process should be waked up either if we get the required resouce or if we recieve any signal (whichever occurs earlier). On other hand down() puts the current process in TASK_UNINTERRUPTIBLE state so it only returns if and only if we are successfull in acquiring a resource. Its advisable to use down_interruptible() than down() in normal cases. Gaurav
Thanks and Regards, Deepak Joshi ________________________________ All new Yahoo! Mail "The new Interface is stunning in its simplicity and ease of use." - PC Magazine
-- Gaurav Email: gauravd.chd@xxxxxxxxx -------------------------------------------- Read my articles at: http://lkdp.blogspot.com -------------------------------------------- Easy to get air tickets at affordable price, US to India Air Tickets: www.Ritz-Travel.com Call at 001-503-848-2299 or mail at info@xxxxxxxxxxxxxxx -------------------------------------------- -- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
