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[Libvir] virConnectGetCapabilities patch, 2007-03-15 (version 2)
by Richard W.M. Jones 15 Mar '07

15 Mar '07

This is the latest version of the capabilities patch, which should address all concerns which have been raised since the last version. Also attached, example XML produced by different backends. Note as before this has not been tested in the Xen case, because I don't have access to a working Xen machine (laptop still broken, desktop still lacking working SATA drivers, other desktop still lacking wired network...). Rich. -- Emerging Technologies, Red Hat http://et.redhat.com/~rjones/ 64 Baker Street, London, W1U 7DF Mobile: +44 7866 314 421 "[Negative numbers] darken the very whole doctrines of the equations and make dark of the things which are in their nature excessively obvious and simple" (Francis Maseres FRS, mathematician, 1759) <capabilities> <host> <cpu> <arch>x86_64</arch> </cpu> </host> <guest> <os_type>hvm</os_type> <arch name="x86_64"> <wordsize>64</wordsize> <emulator>/usr/bin/qemu-system-x86_64</emulator> <domain type="qemu"/> <machine>pc</machine> <machine>isapc</machine> <domain type="kqemu"/> <domain type="kvm"> <emulator>/usr/bin/qemu-kvm</emulator> </domain> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="i686"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu</emulator> <domain type="qemu"/> <machine>pc</machine> <machine>isapc</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="mips"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-mips</emulator> <domain type="qemu"/> <machine>mips</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="mipsel"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-mipsel</emulator> <domain type="qemu"/> <machine>mips</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="sparc"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-sparc</emulator> <domain type="qemu"/> <machine>sun4m</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="ppc"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-ppc</emulator> <domain type="qemu"/> <machine>g3bw</machine> <machine>mac99</machine> <machine>prep</machine> </arch> </guest> </capabilities> <capabilities> <host> <cpu> <arch>x86_64</arch> </cpu> </host> <guest> <os_type>hvm</os_type> <arch name="x86_64"> <wordsize>64</wordsize> <emulator>/usr/bin/qemu-system-x86_64</emulator> <domain type="qemu"/> <machine>pc</machine> <machine>isapc</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="i686"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu</emulator> <domain type="qemu"/> <machine>pc</machine> <machine>isapc</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="mips"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-mips</emulator> <domain type="qemu"/> <machine>mips</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="mipsel"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-mipsel</emulator> <domain type="qemu"/> <machine>mips</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="sparc"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-sparc</emulator> <domain type="qemu"/> <machine>sun4m</machine> </arch> </guest> <guest> <os_type>hvm</os_type> <arch name="ppc"> <wordsize>32</wordsize> <emulator>/usr/bin/qemu-system-ppc</emulator> <domain type="qemu"/> <machine>g3bw</machine> <machine>mac99</machine> <machine>prep</machine> </arch> </guest> </capabilities> <capabilities> <host> <cpu> <arch>i686</arch> <features> <pae/> <nonpae/> </features> </cpu> </host> <guest> <os_type>linux</os_type> <arch name="i686"> <wordsize>32</wordsize> <domain type="test"/> </arch> <features> <pae/> <nonpae/> </features> </guest> </capabilities>

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[Libvir] Proposed XML format for capabilities, with examples [long]
by Richard W.M. Jones 15 Mar '07

15 Mar '07

Lots of people had various things to say about the first capabilities patches (see thread starting here: https://www.redhat.com/archives/libvir-list/2007-March/msg00153.html) So I thought I'd try to pull together ideas into a single thread, and post some information about what this is trying to achieve and some example proposed XML. Motivation ---------- At the moment there is a considerable amount of conditional code in libvirt clients. For example the following code from virt-manager (src/virtManager/create.py): if self.connection.get_type() == "QEMU": <------- 1 self.window.get_widget("virt-method-pv").set_sensitive(False) self.window.get_widget("virt-method-fv").set_active(True) self.window.get_widget("virt-method-fv-unsupported").hide() self.window.get_widget("virt-method-fv-disabled").hide() else: self.window.get_widget("virt-method-pv").set_sensitive(True) self.window.get_widget("virt-method-pv").set_active(True) if virtinst.util.is_hvm_capable(): <--------- 2 self.window.get_widget("virt-method-fv").set_sensitive(True) self.window.get_widget("virt-method-fv-unsupported").hide() self.window.get_widget("virt-method-fv-disabled").hide() This hopefully demonstrates two points which I'd like to fix: Firstly having code which requires knowledge of what a driver is capable of (line 1 above) is not scalable as we add more and more types of virtualisation (OpenVZ, VMWare, ...). Secondly the virtinst.util module does some probing to find out what the local hardware is capable of (line 2 above), and that won't work over remote connections. Thirdly, although you can only really connect to one driver at a time (except in the Xen case, but that's just weird), the <domain> description required by virDomainCreateLinux is to some extent driver-specific. So you need additional logic when creating domains, and for some of those (eg. qemu/kqemu/kvm) it's non-trivial and depends on information that you "just know" about the driver. The proposed new API ("virConnectGetCapabilities") would return an XML description of the capabilities of the driver / hypervisor. In the remote case, probing would be done on the remote machine. In either case the idea would be to remove conditional code from virt-manager, remove local hardware probing from virtinst, and provide some description of what optional features the <domain> XML supports. In the next two sections I'll analyse the problem areas in the current virtinst and virt-manager. You may want to skip the next two sections and go straight to the example XML. Analysis of virtinst -------------------- The main issue is with virtinst/util.py which contains the following functions which do local probing: (1) is_pae_capable: host supports PAE? Uses Linux-specific /proc/cpuinfo (2) is_hvm_capable: host supports HVM & enabled in Xen? Uses Xen-specific /sys/hypervisor/properties/capabilities (3) is_kqemu_capable: [Linux] kernel supports kqemu? Uses Linux-specific /dev/kqemu (4) is_kvm_capable: [Linux] kernel supports kvm? Uses Linux-specific /dev/kvm In virtinst/FullVirtGuest.py: (5) "emulator" and "loader" must be specified for Xen/QEMU and Xen guests respectively. They have architecture- and distro-specific paths which refer to files on the remote machine. In virtinst/ParaVirtGuest.py: (6) Uses "xm console" to connect to the console in the Xen case (but then this sort of paravirtualisation implies Xen). In virtinst/DistroManager.py: (7) We download the kernel and boot.iso files, and download and modify the initrd file. [Comment: I'm not sure that capabilities can solve this, but it does need to be fixed properly for the remote case to work]. Analysis of virt-manager ------------------------ In src/virtManager/create.py: (8) Tries to detect if VT-x/AMD-V is present in the hardware but disabled in the BIOS by doing some Xen-specific heuristics. (9) Paravirt and fullvirt dialogs are enabled based on the type of the connection (eg. if self.connection.get_type() == "QEMU" it disables paravirt). (10) CPU architecture combo box is enabled only for type == "QEMU". (11) Similarly, the "accelerate" checkbox is enabled only for type == "QEMU". [Comment: Dan tells me that this requirement comes about because kqemu is sometimes unreliable, so users need a way to disable it]. (12) Local media are required for FV installs. Also we use HAL to detect media inserted and removed. [Comment: Can be solved separately by abstracting storage]. In the *.glade files: (13) The list of CPU architectures for qemu is hard-coded in the interface description file. Other areas which are beyond the role of capabilities: * Remote console * Serial console * Saving images Proposed XML format ------------------- My thoughts are that capabilities need to return the following information about the underlying driver/hypervisor: * Host CPU flags (1,8) * List of guest architectures supported. For each of these: - Model of virtualised CPU (10,13) example: x86_64 - Name of the virtualised machine (if applic.) example: pc - Virtualised CPU features: PAE, ... - Fullvirt flag: can we run an unmodified OS as a guest? (2,9) or Paravirt: what sort of paravirt API does a guest need (eg. xen, pvops, VMI, ...)? - The <domain type='?'> for this guest example: kqemu - The <domain><os><type machine='?'> for this guest (if applic.) example: pc - Suggested emulator and loader paths (5) - Driver-specific flags which libvirt clients would not be required to understand, but could be used to enhance libvirt clients. examples: uses kqemu, uses kvm (3,4,11) (Notes: (a) I have flattened qemu's nested arch/machine list, because I there is not a natural hierarchy. (b) The guest architectures list is a Cartesian product, although at the moment the worst case (qemu) would only have about 14 entries. An alternate way to do this is discussed at the end. (c) The host CPU model is already provided by virNodeGetInfo). Example: Xen ------------ For Xen the primary source for capabilities are the files /sys/hypervisor/properties/capabilities and /proc/cpuinfo. A Xen driver might present the following description of its capabilities: <capabilities> <host> <cpu_flags> <cpu_flag> vmx </cpu_flag> <cpu_flag> pae </cpu_flag>  </cpu_flags> </host> <guest_architectures> <guest_architecture> <model> x86_64 </model> <paravirt> xen </paravirt> <domain_type> xen </domain_type> <emulator> /usr/lib/xen/bin/qemu-dm </emulator> </guest_architecture> <guest_architecture> <model> i686 </model> <pae/> <paravirt> xen </paravirt> <domain_type> xen </domain_type> <emulator> /usr/lib/xen/bin/qemu-dm </emulator> </guest_architecture> <guest_architecture> <model> i686 </model> <fullvirt/> <domain_type> xen </domain_type> <loader> /usr/lib/xen/boot/hvmloader </loader> <emulator> /usr/lib/xen/bin/qemu-dm </emulator> </guest_architecture> <guest_architecture> <model> i686 </model> <pae/> <fullvirt/> <domain_type> xen </domain_type> <loader> /usr/lib/xen/boot/hvmloader </loader> <emulator> /usr/lib/xen/bin/qemu-dm </emulator> </guest_architecture> <guest_architecture> <model> x86_64 </model> <fullvirt/> <domain_type> xen </domain_type> <loader> /usr/lib/xen/boot/hvmloader </loader> <emulator> /usr/lib/xen/bin/qemu-dm </emulator> </guest_architecture> </guest_architectures> </capabilities> Example: qemu + kqemu + kvm --------------------------- Qemu has by far the longest list of supported guest architectures. Out of the box it supports 10 distinct machine types and then you can add 4 extra machine types if the kernel can do kqemu and kvm, making 14 in all. Below I have abbreviated this list for clarity. <capabilities> <host> <cpu_flags> <cpu_flag> vmx </cpu_flag> <cpu_flag> pae </cpu_flag>  </cpu_flags> </host> <guest_architectures> <guest_architecture> <model> sparc </model> <machine> sun4m </machine> <fullvirt/> <domain_type> qemu </domain_type> <machine_type> sun4m </machine_type> <emulator> /usr/bin/qemu-system-sparc </emulator> </guest_architecture> <guest_architecture> <model> i686 </model> <machine> pc </machine> <fullvirt/> <domain_type> qemu </domain_type> <machine_type> pc </machine_type> <emulator> /usr/bin/qemu </emulator> </guest_architecture> <guest_architecture> <model> x86_64 </model> <machine> pc </machine> <fullvirt/> <domain_type> kqemu </domain_type> <machine_type> pc </machine_type> <emulator> /usr/bin/qemu </emulator> <qemu_uses_kqemu /> </guest_architecture> <guest_architecture> <model> x86_64 </model> <machine> pc </machine> <fullvirt/> <domain_type> kvm </domain_type> <machine_type> pc </machine_type> <emulator> /usr/bin/qemu-kvm </emulator> <qemu_uses_kvm /> </guest_architecture> </guest_architecture> </capabilities> Guest architectures: Cartesian product or UI builder? ----------------------------------------------------- Currently the list of guest architectures is a flat list, worst case 5 entries long for Xen and 14 entries long for qemu. Presenting this in user interfaces could be challenging. One suggestion is that the user interface looks like: [*] Show only fullvirt [*] Show only PC architectures [ ] Show 32 bit architectures [*] Show 64 bit architectures | Shorter list of architectures which match | the criteria checked above. | ... | Another is that we change the XML description so that it matches the UI. For instance: <guest_architecture> <models> <model> sparc </model> <model> ppc </model> ... Or: <pae> <can_enable/> <can_disable/> </pae> This is relatively easy to do with qemu, but the format of Xen's /sys/hypervisor/properties/capabilities makes it quite hard. i18n ---- Some proposed features may make translation challenging. For example qemu supports a whole list of machine types ("pc", "sun4m", etc.) and it would be nice for libvirt clients to be able to provide some sort of description for the user. It would not be wise to carry this description in the XML because it would not be possible to localise it. To avoid all libvirt clients duplicating and maintaining lists of machine types and descriptions, it may be worth adding a call to the API along the lines of: virConnectGetMachineDescription (const char *machine_name, const char *lang); (where lang == NULL would mean to use the current language). [EOF] -- Emerging Technologies, Red Hat http://et.redhat.com/~rjones/ 64 Baker Street, London, W1U 7DF Mobile: +44 7866 314 421 "[Negative numbers] darken the very whole doctrines of the equations and make dark of the things which are in their nature excessively obvious and simple" (Francis Maseres FRS, mathematician, 1759)

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[Libvir] virConnectGetCapabilities patch, 2007-03-15
by Richard W.M. Jones 15 Mar '07

15 Mar '07

The latest version is attached. This should satisfy all concerns which have been raised with the previous versions. Rich. -- Emerging Technologies, Red Hat http://et.redhat.com/~rjones/ 64 Baker Street, London, W1U 7DF Mobile: +44 7866 314 421 "[Negative numbers] darken the very whole doctrines of the equations and make dark of the things which are in their nature excessively obvious and simple" (Francis Maseres FRS, mathematician, 1759)

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[Libvir] [PATCH]fix the judgment of the domain state between hypervisor and xend
by Kazuki Mizushima 15 Mar '07

15 Mar '07

Hi, According to the xm & virsh man page, I make a patch which fixes the judgment of the domain state between xenHypervisorDriver and xenDaemonDriver. Signed-off-by: Kazuki Mizushima <mizushima.kazuk(a)jp.fujitsu.com> Thanks, Kazuki Mizushima Index: xend_internal.c =================================================================== RCS file: /data/cvs/libvirt/src/xend_internal.c,v retrieving revision 1.101 diff -u -p -r1.101 xend_internal.c --- xend_internal.c 8 Mar 2007 14:12:06 -0000 1.101 +++ xend_internal.c 14 Mar 2007 10:42:16 -0000 @@ -1722,9 +1722,9 @@ sexpr_to_xend_domain_info(virDomainPtr d if (strchr(flags, 'c')) info->state = VIR_DOMAIN_CRASHED; else if (strchr(flags, 's')) - info->state = VIR_DOMAIN_SHUTDOWN; - else if (strchr(flags, 'd')) info->state = VIR_DOMAIN_SHUTOFF; + else if (strchr(flags, 'd')) + info->state = VIR_DOMAIN_SHUTDOWN; else if (strchr(flags, 'p')) info->state = VIR_DOMAIN_PAUSED; else if (strchr(flags, 'b'))

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[Libvir] [PATCH] modular compilation of xen/qemu/test
by Daniel Veillard 14 Mar '07

14 Mar '07

The following patch adds 3 configure options to turn on or off the support for Xen, QEMU/KVM and the test driver, as the output of configure --help shows: ... --with-xen add XEN support (on) --with-qemu add QEMU/KVM support (on) --with-test add test driver support (on) ... It uses compile time flags, is not really intrusive, it just pointed out a few strangeness, one of which was fixed (a Xen include) and the remaining ones are: - xml.c doesn't depend on Xen except for virDomainXMLDevID calling xenStoreDomainGetNetworkID() - libvirt.c still calls xenDaemonDomainLookupByName_ids from virDomainGetUUID() , I'm not sure if this can be avoided In the tests directory, sexpr2xmltest.c and xmconfigtest.c still depends on code in xen specific modules, trying to add them without xen being present was more complex than the value it may add (it also makes the patch smaller to cut at the module level). Plan to commit this before the release, unless this raises a problem, Daniel -- Red Hat Virtualization group http://redhat.com/virtualization/ Daniel Veillard | virtualization library http://libvirt.org/ veillard(a)redhat.com | libxml GNOME XML XSLT toolkit http://xmlsoft.org/ http://veillard.com/ | Rpmfind RPM search engine http://rpmfind.net/

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[Libvir] Reliably detecting if Intel VT is disabled in the BIOS
by Richard W.M. Jones 14 Mar '07

14 Mar '07

VMXON is the instruction which turns on Intel VT extensions[1]. This instruction can be enabled and disabled by setting a bit in a CPU register. Moreover, this CPU register itself can be locked so that no changes can be made until the CPU is power-cycled. In detail, the register is the IA32_FEATURE_CONTROL (0x3A) MSR. The relevant bits are: bit 0 Lock bit (0 = unlocked, 1 = permanently locked) bit 1 Enable VMXON in Intel Safer Mode Extensions (SMX) bit 2 Enable VMXON in normal operation So to find out if VT is possible with the CPU, use CPUID (in practice, check if "vmx" is in /proc/cpuinfo flags). To find out if VT can be turned on in the host, check bit 2 in the above register. There is a handy tool called msr-tools[2] which you can use: # ./rdmsr 0x3a ff03 (bit 2 is clear, so VT is _not_ enabled on this host). It seems that the BIOS locks the register (by writing 1 to bit 0). To find out if the BIOS has locked the register, use rdmsr again and look at the lowest bit. In the example above you can see that the BIOS disabled VT and locked the register. Once the register is locked, the only way around it is to reboot. If the register is unlocked you can enable VT by writing a 1 to bit 2. If you don't want to use the msr-tools, then direct access to the register can be had through /dev/cpu/<id>/msr. For example this is an strace of rdmsr 0x3a: open("/dev/cpu/0/msr", O_RDONLY) = 3 pread(3, "\3\377\0\0\0\0\0\0", 8, 58) = 8 However you need to be root to open /dev/cpu/0/msr. On machines which don't support the IA32_FEATURE_CONTROL MSR you will get an EIO error: pread(3, 0x7ffff81ec810, 8, 58) = -1 EIO (Input/output error) Rich. Notes: [1] I don't think this is possible with AMD's Pacifica extensions. I'm not sure if it's possible to disable these in the BIOS & lock them. [2] http://www.kernel.org/pub/linux/utils/cpu/msr-tools/ Sources: * linux/drivers/kvm/vmx.c: function vmx_disabled_by_bios * "Intel® Trusted Execution Technology Preliminary Architecture Specification" section 2.1.2 (http://download.intel.com/technology/security/downloads/31516803.pdf) -- Emerging Technologies, Red Hat http://et.redhat.com/~rjones/ 64 Baker Street, London, W1U 7DF Mobile: +44 7866 314 421 "[Negative numbers] darken the very whole doctrines of the equations and make dark of the things which are in their nature excessively obvious and simple" (Francis Maseres FRS, mathematician, 1759)

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[Libvir] [PATCH] Add virConnectGetCapabilities call to return the capabilities of the driver / hypervisor
by Richard W.M. Jones 13 Mar '07

13 Mar '07

This patch: * Adds virConnectGetCapabilities which returns an XML description of the capabilities of the driver or hypervisor under this connection (see below for more about the XML format). * Adds virsh capabilities command. * Checks the Python binding works. Caveats: * Xen implementation (in xen_internal.c) is not tested because I don't have a working Xen machine right now. QEMU, test and remote work however. Example: $ virsh -c test:///default capabilities | tidy -xml -i -q <capabilities> <domain> <type>test</type> </domain> <host_features></host_features> <guest_architectures> <guest_architecture> <model>i686</model> <bits>32</bits> <guest_features> <accelerated /> <pae /> </guest_features> </guest_architecture> </guest_architectures> </capabilities> $ virsh -c qemu:///session capabilities | tidy -xml -i -q <capabilities> <domain> <type>qemu</type> </domain> <guest_architectures> <guest_architecture> <model>i686</model> <bits>32</bits> <features> <emulated /> </features> </guest_architecture> <guest_architecture> <model>x86_64</model> <bits>64</bits> <features> <emulated /> </features> </guest_architecture> [... other archs deleted ...] </guest_architectures> </capabilities> XML format: The <capabilities> node contains information about the host and a list of supported architectures for guests. About the host we return: <domain> <type> The default type acceptable when creating a domain. <host_features> <hvm> Does the host CPU support HVM? <type> Type of HVM (eg. "vmx") <bios_setting> "enabled" or "disabled" About the guest architectures we can return: <guest_architecture> <model> The (virtualised) CPU <bits> Bits <domain> <type> If different from the default type (eg. for kqemu) <features> <hvm> Full virt guest? <accelerated> Accelerated (eg. Xen or kqemu) <emulated> Emulated (eg. qemu or bochs) (and a few other esoteric flags here) Rich. -- Emerging Technologies, Red Hat http://et.redhat.com/~rjones/ 64 Baker Street, London, W1U 7DF Mobile: +44 7866 314 421 "[Negative numbers] darken the very whole doctrines of the equations and make dark of the things which are in their nature excessively obvious and simple" (Francis Maseres FRS, mathematician, 1759)

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[Libvir] virsh command is getting a connecting error
by Saori Fukuta 13 Mar '07

13 Mar '07

Hi, It was working fine on March 8th, but today it failed to do virsh command with an error message. # virsh list libvir: error : no support for hypervisor lt-virsh: error: failed to connect to the hypervisor This message is printed here because nb_network_drivers is 0. --- libvirt.c : virConnectOpen 317 if (ret->nb_drivers == 0 || ret->nb_network_drivers == 0) { 318 /* we failed to find an adequate driver */ 319 virLibConnError(NULL, VIR_ERR_NO_SUPPORT, name); 320 goto failed; 321 } I think the cause is because it failed to bind the socket at qemuOpenClientUNIX. --- qemu_internal.c : qemuOpenClientUNIX 232 /* 233 * now bind the socket to that address and listen on it 234 */ 235 if (connect(fd, (struct sockaddr *) &addr, sizeof(addr)) < 0) { They are setting members of sockaddr: {sun_family = 1, sun_path = "/usr/var/run/libvirt/qemud-sock", '\0'} and connect returned -1 with errno that was 2(ENOENT). Is there any problem? Please tell me how I can use current virsh command. Thanks, Saori Fukuta.

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[Libvir] Inconsistent networking between Xen & QEMU
by Daniel P. Berrange 09 Mar '07

09 Mar '07

In Xen it is possible to configure a VIF to enslave with an arbitrary bridge device using a fragment of XML like: <interface type='bridge'> <source bridge='xenbr0'/> <mac address='00:16:3E:66:94:9C'/> </interface> In this example I've enslaved to xenbr0 which is created by the Xen networking script, but this will work with any bridge device really. In QEMU the only bridging is available via the 'virtual networks' support in libvirt, by referencing a named bridge. For example <interface type='network'> <source network='default'/> <mac address='00:16:3E:66:94:9C'/> </interface> Now 'default' is merely defined to be backed by a bridge device 'virbr0' (although it does not neccessary get backed by a bridge) so the basic impl is basically just enslaving a TAP device. Anyway, we now have two different syntaxes in the XML for defining what is more or less the same thing which is a real PITA for the tools. It is useful to have the distinct representations - one is for 'managed' bridges, and the other is for 'unmanaged' bridges - we can do some much more interesting things with managed bridges. To improve life for the tools though I'd like to do two things as a high priority - Support managed networks in Xen - we can simply lookup the bridge device associated with a network and tell Xen to use vif-bridge with this device. For the reverse Xen will tell us what bridge device a guest is using, and we can reverse lookup the corresponding network - Support non-managed networks in QEMU - we can simply enslave the QEMU tap device to an arbitrary user specific bridge device. Until one of these two options is done, its going to be a PITA to support networking across QEMU & Xen in virt-manager/virt-install. Regards, Dan. -- |=- Red Hat, Engineering, Emerging Technologies, Boston. +1 978 392 2496 -=| |=- Perl modules: http://search.cpan.org/~danberr/ -=| |=- Projects: http://freshmeat.net/~danielpb/ -=| |=- GnuPG: 7D3B9505 F3C9 553F A1DA 4AC2 5648 23C1 B3DF F742 7D3B 9505 -=|

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[Libvir] [PATCH] Add a default network
by Mark McLoughlin 09 Mar '07

09 Mar '07

Hey, So, we want to install a default network which guests can connect to. This can be seen as e.g. a replacement for xenbr0 as the default bridge for xen guests. A few things concern me about the patch, see below for my thinking. However, I'm happy to punt on all of these issues for now and go ahead with the patch. 1) Ordering - we want the default network to have a predictable bridge name, so instead of relying on it being the first network and ending up auto-allocated vnet0, we use virbr0. The alternative is to actually have an ordering scheme, e.g. #define LIBVIRT_AUTOSTART_PRIORITY_DISABLE -1 #define LIBVIRT_AUTOSTART_PRIORITY_FIRST 0 #define LIBVIRT_AUTOSTART_PRIORITY_LAST 99 #define LIBVIRT_AUTOSTART_PRIORITY_DEFAULT 50 int virNetworkSetAutostart(virDomainPtr domain, int priority); autostart/00-default.xml -> ../default.xml autostart/99-MyNetwork.xml -> ../MyNetwork.xml Maybe that's useful, but probably moreso for guests than networks. The "virbr0" solution is fine, IMHO. 2) IP address choice - I've randomly chosen 192.168.122.1/24 as the IP address for the network, and this could happen to clash with an existing network. Since we masquerade outgoing traffic, I think the only problem this would cause in practice would be where the host machine is already on a 192.168.122/24 subnet and it could find itself connecting to a guest rather than another machine on the physical subnet. It's a default configuration choice which admins can change, and I don't see it causing huge problems in practice, so I'm not overly concerned. If it did turn out to be a problem, I'd probably add something like: <ip type="auto" /> But I'm not anxious to go down that route right now. 3) UUID generation - there's no UUID specified, so the default network will have a different UUID across reboots. We could trivially save the UUID at first boot, but we'd really need to put it in /var then. IMHO, it's something we can fix later if it turns out to be important. Cheers, Mark.

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