On Fri, Sep 18, 2009 at 9:07 PM, Leonidas . <leonidas137@xxxxxxxxx> wrote: > > > On Fri, Sep 18, 2009 at 5:36 AM, Peter Teoh <htmldeveloper@xxxxxxxxx> wrote: >> >> > >> > I think you are talking about ioctl on a single minor number device, my >> > concern is more >> > about choice here. Meaning whether using ioctls with different commands >> > on a >> > single dev >> > node be preferable to issuing reads on 3 different minor number device >> > nodes. >> > >> > >> > -Leo. >> > >> > >> >> just take the example of major device no 1: u have /dev/mem, >> /dev/kmem, /dev/null, /dev/port etc etc....all having same major but >> different minor number, and implementation functions spilled into >> mem.c, or random.c etc, ie, more codes, more global variables (the >> fops structures) and more kernel memory (> 6MB++?). but then u have >> the simplicity of coding (userspace) as well as asynchronous access to >> the kernel - ie, all three read() can enter the kernel at the same >> time. >> >> but if u used just one minor for 3 different buffer, and do some >> sophisticated multiplexing, u saved on memory (2MB++), but programming >> is more complex (userspace + kernel - those multiplexing stuff). and >> u need to issue the read() synchronously - and u can either use >> in-band (or in-channel, hope u know what I mean) signalling (meaning >> the identifier of the buffer type is inside the buffer itself), or >> simpler still is out-of-band signalling (or side-channel), so in this >> case u need another minor device for ioctl purpose, to signal the >> buffer type to be used for the first minor device. ie, read() for >> first minor device, and ioctl() for 2nd minor device? does it make >> any sense? >> >> >> -- >> Regards, >> Peter Teoh > > Peter, > > You explained the first part in a fantastic way! > But I am not sure about the second para, in/out-band stuff. > > -Leo > ok......by in-band, i mean data + buffer type descriptor (u have 3 types of buffer right) all goes into the same data area, so perhaps 2MB + 1 byte (which will have values of 1,2, or 3 to identify which buffer the current data represent). so basically only ONE device (eg, /dev/myA). by out-of-band, i mean data will go into /dev/myA, and buffer type will go into /dev/myB. so u do ioctl(/dev/myB) to specify the buffer type, and then the entire 2MB will go into /dev/myA. so basically TWO device have to be created. -- Regards, Peter Teoh -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
