Re: Issue with limitation of 256 minors per major in LiS 2.16 on Linu x 2.4

LiS has the status of a file system in the Linux kernel.  That means that 
it can define its own interpretation for dev_t structures.  Since LiS-2.17 
it has maintained an internal dev_t with 12 bits of major and 20 bits of minor.

If you are operating clone devices then the external 8/8 restrictiveness is 
not something that you have to be concerned about.  With clone devices you 
only need one node in /dev for your clone device, and this can fit into the 
8/8 representation of the ext2 file system.  Internally in your driver's 
open routine you can just compute a 20 bit minor device number and return it.

If you need thousands of visible device nodes in /dev then you still need 
to use the multiple-major trick because the external ext2 file system is 
still 8/8.

-- Dave

At 01:25 PM 10/6/2004, Eashwaran, P wrote:
>I tried to check if this issue has been addressed in previous archives, 
>but clicking on 
><http://gsyc.escet.urjc.es/mailarchive/linux-streams>http://gsyc.escet.urjc.es/mailarchive/linux-streams 
>gives me a "Forbidden" error page!    So, here it is again!  Please feel 
>free to forward me links of older archives if this issue has been 
>previously discussed in this forum.
>
>Linux 2.4 allows only 256 minors per major.  This is a severe restriction 
>for us.  Our driver ports on other OSes allow for 1000+ devices.  With the 
>current major/minor allocation scheme on Linux 2.4 we are now limited to 
>only 256 devices.
>
>Our user applications know only to open one device file which has major of 
>the LiS clone_drvr and minor as the actual STREAMS device's major number.
>
>In other discussions of this topic, I have seen suggestions where the user 
>application opens different device names.
>All our applications work with one device file, so we cannot have multiple 
>device files with differing major numbers each supporting 256 devices.
>
>Currently, the driver uses dynamic allocation with lis_register_strdev 
>(with 0 arg) to obtain they major number dynamically.  Reading a few links 
>on the web related to this (like 
><http://www.mail-archive.com/[email protected]/msg00269.html>http://www.mail-archive.com/[email protected]/msg00269.html) 
>I've found that one can call the lis_register_strdev multiple times to get 
>multiple major numbers.
>
>I can do that in my driver and have an array of 4 major numbers each 
>capable of 256 minor numbers.  My question is: when I return from 
>device_open routine, if I change the major number of the device to another 
>major number (allocated for the same driver) will it work?
>
>Lets say that I've majors 248, 250, 247, 253 in that order in my array of 
>4 allocated major numbers for my driver, because I called 
>lis_register_strdev 4 times.  Also, lets say that I'm able to lookup an 
>internal array of 1024 minor devices and am able to determine which one is 
>free to use.  Having said that, if I modify the *devp parameter in the 
>device_open by changing the major number AND minor number and returning 
>from the routine, will that work?  Note that the major/minor pair is still 
>going to map to one of the major numbers that I've allocated dynamically.
>
>Even if the above strategy is alright, do you think it will still work 
>even if my driver uses locks.  Currently I use 2 lis_rw_lock_t and 1 
>lis_spin_lock_t structures to safeguard common data and critical sections.
>
>The only disadvantage is that there are a limited number of major numbers 
>available.  Linux 2.6 is supposedly going to address this shortage by 
>increasing the number of minors per major and also increasing the number 
>of majors in the system.
>
>Any help is appreciated.
>
>Thanks & Regards,
>Eashwaran.
>