Re: support of older compilers [u]

[Grzegorz Kulewski <kangur@polcom.net>]

On Sat, 6 Nov 2004, Martin Schlemmer [c] wrote:

> On Fri, 2004-11-05 at 22:59 +0100, Grzegorz Kulewski wrote:
>>> The kernel does do more these days than it did in '95. But 6 times more? I
>>> dunno..
>>
>> Can't we remove ramfs for a good start? Everyone should use tmpfs instead
>> and some stupid distributions (I will not tell their names) try to mount
>> ramfs on /dev (udev) and that leads to very stupid panic if you will
>> write for example:
>>
>> dd if=/dev/evms/sda5 of=/dev/sda17 bs=1024
>>
>> instead of "of=/dev/evms/sda17".
>>
>> Explanation (if anybody needs one):
>> Kernel can't create more partition devices than 15 for SCSI and SATA disks
>> because of lack of minor numbers. So I am using evms to create these
>> devices. So I should use /dev/evms/sda* for these partitions. And if I
>> will not remember to do so then I will get oom panic very shortly because
>> ramfs is not limited (in contrary to tmpfs).
>>
>> And this kind of stupid mistake can happen. It happened to me 3 times in a
>> row before I started to debug what is wrong with this kernel.
>>
>> [BTW. Does somebody know how to tell the kernel that I do not want
>> /dev/sda[0-9]* files (but I do want /dev/hda files) created == I do not
>> want kernel partition driver to touch this particular device?]
>>
>
> So basically /dev/sda* have major of scsi, and /dev/evms/sda* have major
> of evms, and you end up using the wrong nodes?

Not exactly. I end up creating really big, growing, file on no limit RAM 
backed filesystem. EVMS locks standard devices, so I probably can not run 
something like:

dd if=/dev/sda5 of=/dev/sda6 bs=1024

because it will return "device busy" error or something like that. But I 
didn't test it. But I tested (in the most painful way) that

mount -t ext2 /dev/sda5 /mnt/foo

will not work because of this error.

And EVMS has no major numbers. It is purely user space. It uses 
device-mapper for creating devices and uses device-mapper's major number.

And yes, I probably can force UDEV to stop creating /dev/sda[0-9]* 
devices, but this is not the right solution I think. These config files 
are managed by my distribution and are complicated. I do not want to have 
to merge them with updates every time new UDEV is released. Besides I want 
to disable kernel partition discovery just for this device. This will be 
ugly excaption.


Thanks,

Grzegorz Kulewski