ce5aebeacd
When an nwfilter rule sets the parameter CTRL_IP_LEARNING to "dhcp", this turns on the "dhcpsnoop" thread, which uses libpcap to monitor traffic on the domain's tap device and extract the IP address from the DHCP response. If libpcap on the host is built with HAVE_TPACKET3 defined (to enable support for TPACKET_V3), the dhcpsnoop code's initialization of the libpcap socket would fail with the following error: virNWFilterSnoopDHCPOpen:1134 : internal error: pcap_setfilter: can't remove kernel filter: Bad file descriptor It turns out that this was because TPACKET_V3 requires a larger buffer size than libvirt was setting (we were setting it to 128k). Changing the buffer size to 256k eliminates the error, and the dhcpsnoop thread once again works properly. A fuller explanation of why TPACKET_V3 requires such a large buffer, for future git spelunkers: libpcap calls setsockopt(... SOL_PACKET, PACKET_RX_RING...) to setup a ring buffer for receiving packets; two of the attributes sent to this API are called tp_frame_size, and tp_frame_nr. If libpcap was built with HAVE_TPACKET3 defined, tp_trame_size is set to MAXIMUM_SNAPLEN (defined in libpcap sources as 262144) and tp_frame_nr is set to: [the buffer size we set, i.e. PCAP_BUFFERSIZE i.e. 262144] / tp_frame_size. So if PCAP_BUFFERSIZE < MAXIMUM_SNAPLEN, then tp_frame_nr (the number of frames in the ring buffer) is 0, which is nonsensical. This same value is later used as a multiplier to determine the size for a call to malloc() (which would also fail). (NB: if HAVE_TPACKET3 is *not* defined, then tp_frame_size is set to the snaplen set by the user (in our case 576) plus a small amount to account for ethernet headers, so 256k is far more than adequate) Since the TPACKET_V3 code in libpcap actually reads multiple packets into each frame, it's not a problem to have only a single frame (especially when we are monitoring such infrequent traffic), so it's okay to set this relatively small buffer size (in comparison to the default, which is 2MB), which is important since every guest using dhcp snooping in a nwfilter rule will hold 2 of these buffers for the entire life of the guest. Thanks to Christian Ehrhardt for discovering that buffer size was the problem (this was not at all obvious from the error that was logged!) Resolves: https://bugzilla.redhat.com/1547237 Fixes: https://bugs.launchpad.net/libvirt/+bug/1758037 Signed-off-by: Laine Stump <laine@laine.org> Reviewed-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> (V1) Reviewed-by: John Ferlan <jferlan@redhat.com> Tested-by: Christian Ehrhardt <christian.ehrhardt@canonical.com> |
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| AUTHORS.in | ||
| autogen.sh | ||
| bootstrap | ||
| bootstrap.conf | ||
| cfg.mk | ||
| ChangeLog-old | ||
| config-post.h | ||
| configure.ac | ||
| COPYING | ||
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| libvirt-admin.pc.in | ||
| libvirt-lxc.pc.in | ||
| libvirt-qemu.pc.in | ||
| libvirt.pc.in | ||
| libvirt.spec.in | ||
| Makefile.am | ||
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| README | ||
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Libvirt API for virtualization
Libvirt provides a portable, long term stable C API for managing the virtualization technologies provided by many operating systems. It includes support for QEMU, KVM, Xen, LXC, bhyve, Virtuozzo, VMware vCenter and ESX, VMware Desktop, Hyper-V, VirtualBox and the POWER Hypervisor.
For some of these hypervisors, it provides a stateful management daemon which runs on the virtualization host allowing access to the API both by non-privileged local users and remote users.
Layered packages provide bindings of the libvirt C API into other languages including Python, Perl, PHP, Go, Java, OCaml, as well as mappings into object systems such as GObject, CIM and SNMP.
Further information about the libvirt project can be found on the website:
License
The libvirt C API is distributed under the terms of GNU Lesser General
Public License, version 2.1 (or later). Some parts of the code that are
not part of the C library may have the more restrictive GNU General
Public License, version 2.1 (or later). See the files COPYING.LESSER
and COPYING for full license terms & conditions.
Installation
Libvirt uses the GNU Autotools build system, so in general can be built and installed with the usual commands. For example, to build in a manner that is suitable for installing as root, use:
$ ./configure --prefix=/usr --sysconfdir=/etc --localstatedir=/var
$ make
$ sudo make install
While to build & install as an unprivileged user
$ ./configure --prefix=$HOME/usr
$ make
$ make install
The libvirt code relies on a large number of 3rd party libraries. These will
be detected during execution of the configure script and a summary printed
which lists any missing (optional) dependencies.
Contributing
The libvirt project welcomes contributions in many ways. For most components the best way to contribute is to send patches to the primary development mailing list. Further guidance on this can be found on the website:
https://libvirt.org/contribute.html
Contact
The libvirt project has two primary mailing lists:
- libvirt-users@redhat.com (for user discussions)
- libvir-list@redhat.com (for development only)
Further details on contacting the project are available on the website: