Re: Disk naming (Was Re: [Xen-devel] [PATCH] Guest boot loadersupport [1/2])

[Adam Heath <doogie@xxxxxxxxxxxxx>]

On Fri, 15 Apr 2005, Mark Williamson wrote:

> > The blkfront driver should request id+offset+length from the blkback
> > driver. The blkback driver then converts the id into either a device, or a
> > file. Seems rather straight forward to me.
>
> OK, it's not a very cunning hack to do but it makes the blkback driver more
> complex whilst duplicating functionality that's already in the kernel.  You'd
> have to deal with a load of VFS APIs as well as the existing block APIs,
> which would be unfortunate.

Maybe reuse the loopback code?  Maybe it has an abstract device->file
conversion group of functions/structures.

> Does anybody know why the existing loopback device performs badly anyway?  As
> Adam says, it shouldn't be rocket science to make it work well...

Default kernel limit of 8 loops.  Requires a recompile, and then probably only
supports 256 devices max.

> > blktap?  Is that similiar to what I described above?
>
> Blktap allows you to write a userspace program to provide a block device to
> another domain.  It makes what you described a bit more straightforward than
> implementing directly in the blkback driver.

That would be more complex I would think then doing file access in the kernel.

_______________________________________________
Xen-devel mailing list
Xen-devel@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-devel