[libvirt] [PATCH 5/5] conf: Check for hostdev conflicts when assign default disk address

[John Ferlan]

On 07/16/2015 08:23 AM, Ján Tomko wrote:
> On Mon, Jun 22, 2015 at 05:05:07PM -0400, John Ferlan wrote:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1210587  (completed)
>>
>> When generating the default drive address for a SCSI <disk> device,
>> check the generated address to ensure it doesn't conflict with a SCSI
>> <hostdev> address. The <disk> address generation algorithm uses the
>> <target> "dev" name in order to determine which controller and unit
>> in order to place the device. Since a SCSI <hostdev> device doesn't
>> require a target device name, its placement on the guest SCSI address
>> "could" conflict.  For instance, if a SCSI <hostdev> exists at
>> controller=0 unit=0 and an attempt to hotplug 'sda' into the guest
>> made, there would be a conflict if the <hostdev> is already using
>> /dev/sda.
>>
>> Signed-off-by: John Ferlan <jferlan at redhat.com>
>> ---
>>  src/conf/domain_conf.c  | 40 +++++++++++++++++++++++++++++-----------
>>  src/conf/domain_conf.h  |  3 ++-
>>  src/qemu/qemu_command.c |  4 ++--
>>  src/vmx/vmx.c           | 22 ++++++++++++----------
>>  src/vmx/vmx.h           |  3 ++-
>>  5 files changed, 47 insertions(+), 25 deletions(-)
>>
>> diff --git a/src/conf/domain_conf.c b/src/conf/domain_conf.c
>> index 6259d4a..0999e86 100644
>> --- a/src/conf/domain_conf.c
>> +++ b/src/conf/domain_conf.c
>> @@ -5672,7 +5672,8 @@ virDomainDiskFindByBusAndDst(virDomainDefPtr def,
>>  
>>  int
>>  virDomainDiskDefAssignAddress(virDomainXMLOptionPtr xmlopt,
>> -                              virDomainDiskDefPtr def)
>> +                              virDomainDiskDefPtr def,
>> +                              const virDomainDef *vmdef)
>>  {
>>      int idx = virDiskNameToIndex(def->dst);
>>      if (idx < 0) {
>> @@ -5683,7 +5684,10 @@ virDomainDiskDefAssignAddress(virDomainXMLOptionPtr xmlopt,
>>      }
>>  
>>      switch (def->bus) {
>> -    case VIR_DOMAIN_DISK_BUS_SCSI:
>> +    case VIR_DOMAIN_DISK_BUS_SCSI: {
>> +        unsigned int controller;
>> +        unsigned int unit;
>> +
>>          def->info.type = VIR_DOMAIN_DEVICE_ADDRESS_TYPE_DRIVE;
>>  
>>          if (xmlopt->config.hasWideSCSIBus) {
>> @@ -5692,22 +5696,36 @@ virDomainDiskDefAssignAddress(virDomainXMLOptionPtr xmlopt,
>>               * Unit 7 is the SCSI controller itself. Therefore unit 7
>>               * cannot be assigned to disks and is skipped.
>>               */
>> -            def->info.addr.drive.controller = idx / 15;
>> -            def->info.addr.drive.bus = 0;
>> -            def->info.addr.drive.unit = idx % 15;
>> +            controller = idx / 15;
>> +            unit = idx % 15;
>>  
>>              /* Skip the SCSI controller at unit 7 */
>> -            if (def->info.addr.drive.unit >= 7)
>> -                ++def->info.addr.drive.unit;
>> +            if (unit >= 7)
>> +                ++unit;
>>          } else {
>>              /* For a narrow SCSI bus we define the default mapping to be
>>               * 7 units per bus, 1 bus per controller, many controllers */
>> -            def->info.addr.drive.controller = idx / 7;
>> -            def->info.addr.drive.bus = 0;
>> -            def->info.addr.drive.unit = idx % 7;
>> +            controller = idx / 7;
>> +            unit = idx % 7;
>> +        }
>> +
> 
> This mixes non-functional and functional changes.
> 

OK - I can separate out out just the non-functional into its own patch.
 Do you want me to send it out again or trust that I know what I'm doing?

>> +        if (virDomainDriveAddressIsUsedByHostdev(vmdef,
>> +                                                 VIR_DOMAIN_HOSTDEV_SUBSYS_TYPE_SCSI,
>> +                                                 controller, 0, 0, unit)) {
>> +            virReportError(VIR_ERR_XML_ERROR,
>> +                           _("address generated using disk target name '%s' "
>> +                             "may conflict with SCSI host device address "
>> +                             "controller='%u' bus='%u' target='%u' unit='%u"),
>> +                           def->dst, controller, 0, 0, unit);
> 
> 'may conflict' sounds ambiguous. Either it does conflict and we should
> reject it, or it does not and there is no error.
> 
> And this seems like a problem of libvirt's address generation algorithm,
> not an XML error.
> 
> Jan
> 

Right - it does conflict...

The issue is that the 'idx' is generated as a result of the target
device name ("dst").  The assumption being "sda" would be controller =
unit = 0, 'sdb' would be ctlr = 0, unit = 1, 'sdc' would be ctlr = 0,
unit = 2, etc.

However, for hostdev's there is no such "dst" logic - it's a straight
assignment.

When the guest boots, whatever is assigned to "c = 0, u = 0" is assigned
to 'sda' (regardless of whether it's a hostdev or disk).

So if the hostdev which had it's address provided in the XML, but the
disk which didn't *and* is using "<target dev='sda'.../>", then there's
a possible conflict because "sda" resolves to "c = 0, b = 0".  The error
message I guess should thus state :

"using disk target name '%s' conflicts with SCSI host device address ..."

Would you still call that an XML error or perhaps CONFIG_UNSUPPORTED

John