On Sat, Mar 2, 2019 at 1:45 PM <valdis.kletnieks@xxxxxx> wrote: > > On Fri, 01 Mar 2019 23:29:53 -0500, Jeffrey Walton said: > > > I cannot seem to open the device in exclusive mode. The current open > > is (I also tried with O_EXCL): > > > > int modem = open(device_path, O_RDWR | O_NOCTTY | O_SYNC); > > So what happens? Does the open fail? If so, what does perror() say about it? > Or does the open work but the flag is ignored? Yes, both are allowed to open the device. > Have you tried making the *other* program open it with O_EXCL so your > caller-id program can't mess with its state? Yes, I used O_EXCL . I have no control over other programs (this is the reason I can't use something like a named semaphore or lock file). I can say when I write a second test program that uses O_EXCL, it is also allowed to open the device even when the device was already opened O_EXCL. I feel like I am missing something... Does Linux consider the modem a shared resource instead of an exclusive resource? What use cases support two different programs sending commands to the modem at the same time? Jeff _______________________________________________ Kernelnewbies mailing list Kernelnewbies@xxxxxxxxxxxxxxxxx https://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
