2013/10/22 Philippe Gerum <r...@xenomai.org> > On 10/22/2013 06:45 PM, Kim De Mey wrote: > >> >> >> >> 2013/10/19 Ronny Meeus <ronny.me...@gmail.com >> <mailto:ronny.me...@gmail.com>**> >> >> >> >> IIUC, this would add the quite unexpected requirement of having >> to reopen a file for getting fresh data. read() should actually >> (re-)read the current object state each time it is invoked, and >> not resend some frozen state collected by the corresponding >> open() indefinitely. >> >> e.g. this has to work with code like: >> >> fd = open("/mnt/xenomai/1235/foo/__**tasks", O_RDONLY); >> >> for (;;) { >> ret = read(fd, buf, sizeof(buf)); >> ... process NEW data ... >> } >> >> Philippe, >> how to handle the case where the data is bigger than de buffer >> passed by the user? >> Suppose the task data is 20k while the user read only wants 4k. I >> would expect that the second read returns the second 4k block and so >> on. >> By generating the complete output in 1 shot (for example at open), >> the data would be more consistent in my opinion too. >> Suppose the data of a queue is dumped and the queue contains a lot >> of messages. I would like to see a consistent view on the queue and >> not the first 4k followed by some random messages after it because >> the application is processing the queue in parallel. >> >> Philippe, >> >> As Ronny explains, the reason of "storing the state" at open is so that >> the data we read would be consistent. So yes, I think we need this. >> >> > I don't think so. Implementing a snapshot mechanism so that reading from a > channel does return a consistent set of data does not mean that we should > do this in open(). This only means that we should implement a snapshot > mechanism for reading. >
I meant that we need to be able to "store the state", not that we necessary need to do it in the open(). My sentence was confusing, sorry. As I explained further in my previous post we could do it in the initial read() like it is done in sysfs for example. Kim _______________________________________________ Xenomai mailing list Xenomai@xenomai.org http://www.xenomai.org/mailman/listinfo/xenomai
