Re: support of older compilers [u]

[Grzegorz Kulewski]

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

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