Re: 64-bit kdev_t - just for playing

[H. Peter Anvin]

Followup to:  <[e-mail]>
By author:    Badari Pulavarty <[e-mail]>
In newsgroup: linux.dev.kernel
> 
> Roman,
> 
> Here is the patch for sd to allow more than 256 disks.
> There are few issues with the patch that need to be resolved.
> 
> 1) With the patch I get 16 bits for minor. Since 4 bits are used for
> partition, we get 12 bits to represent disks. So each major can support
> 2^12 =3D 4096 disks. Disks 0 - 4095 are mapped to major=3D8,=20
> disks 4096 - 8191 to major =3D 65 and so on..
> 
> This means ..
> 
> (i) I need to create nodes in /dev/ to match new <major, minor> for=20
> these disks.  Currently "mknod" is broken due to glibc issues with dev_t.
> 
> (ii) We need to worry about backward compatibility. For example:
> 17th disk used to have <65, 0>. Now its major, minor is <8, 256>.
> So /dev/ entires need to be re-created to match these, everytime
> you reboot 2.4/2.5 etc. Greg KH udev might fix this for us.=20
> 
> 2) Do we still need 16 majors for disks ?
> 

No, we don't.  On the other hand, we really should change to 64
partitions/disk, same as for non-SCSI disks.  16 really is too small.

	-hpa

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