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[Xen-devel] Re: [RFC PATCH 35/35] Add Xen virtual block device driver.

Chris Wright wrote:
The block device frontend driver allows the kernel to access block
devices exported exported by a virtual machine containing a physical
block device driver.

+static struct xlbd_type_info xlbd_ide_type = {
+       .partn_shift = 6,
+       .disks_per_major = 2,
+       .devname = "ide",
+       .diskname = "hd",
+static struct xlbd_type_info xlbd_scsi_type = {
+       .partn_shift = 4,
+       .disks_per_major = 16,
+       .devname = "sd",
+       .diskname = "sd",
+static struct xlbd_type_info xlbd_vbd_type = {
+       .partn_shift = 4,
+       .disks_per_major = 16,
+       .devname = "xvd",
+       .diskname = "xvd",

This is another thing that has always put me off. The virtual block device driver has the ability to masquerade as other types of block devices. It actually claims to be an IDE or SCSI device allocating the appropriate major/minor numbers.

This seems to be pretty evil and creating interesting failure conditions for users who load IDE or SCSI modules. I've seen it trip up a number of people in the past. I think we should only ever use the major number that was actually allocated to us.


Anthony Liguori

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