libvirt/src
Daniel P. Berrange eca72d4759 Introduce an internal API for handling file based lockspaces
The previously introduced virFile{Lock,Unlock} APIs provide a
way to acquire/release fcntl() locks on individual files. For
unknown reason though, the POSIX spec says that fcntl() locks
are released when *any* file handle referring to the same path
is closed. In the following sequence

  threadA: fd1 = open("foo")
  threadB: fd2 = open("foo")
  threadA: virFileLock(fd1)
  threadB: virFileLock(fd2)
  threadB: close(fd2)

you'd expect threadA to come out holding a lock on 'foo', and
indeed it does hold a lock for a very short time. Unfortunately
when threadB does close(fd2) this releases the lock associated
with fd1. For the current libvirt use case for virFileLock -
pidfiles - this doesn't matter since the lock is acquired
at startup while single threaded an never released until
exit.

To provide a more generally useful API though, it is necessary
to introduce a slightly higher level abstraction, which is to
be referred to as a "lockspace".  This is to be provided by
a virLockSpacePtr object in src/util/virlockspace.{c,h}. The
core idea is that the lockspace keeps track of what files are
already open+locked. This means that when a 2nd thread comes
along and tries to acquire a lock, it doesn't end up opening
and closing a new FD. The lockspace just checks the current
list of held locks and immediately returns VIR_ERR_RESOURCE_BUSY.

NB, the API as it stands is designed on the basis that the
files being locked are not being otherwise opened and used
by the application code. One approach to using this API is to
acquire locks based on a hash of the filepath.

eg to lock /var/lib/libvirt/images/foo.img the application
might do

   virLockSpacePtr lockspace = virLockSpaceNew("/var/lib/libvirt/imagelocks");
   lockname = md5sum("/var/lib/libvirt/images/foo.img");
   virLockSpaceAcquireLock(lockspace, lockname);

NB, in this example, the caller should ensure that the path
is canonicalized before calculating the checksum.

It is also possible to do locks directly on resources by
using a NULL lockspace directory and then using the file
path as the lock name eg

   virLockSpacePtr lockspace = virLockSpaceNew(NULL);
   virLockSpaceAcquireLock(lockspace, "/var/lib/libvirt/images/foo.img");

This is only safe to do though if no other part of the process
will be opening the files. This will be the case when this
code is used inside the soon-to-be-reposted virlockd daemon

Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
2012-10-16 15:45:55 +01:00
..
conf conf: Fix crash with cleanup 2012-10-16 11:15:04 +02:00
cpu maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
esx esx: Fix dynamic dispatch for types with more than one level of inheritance 2012-10-09 23:02:39 +02:00
hyperv hyperv: Fix and improve hypervListAllDomains 2012-09-29 21:06:46 +02:00
interface maint: prepare for next release number 2012-10-16 08:09:01 -06:00
libxl maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
locking locking: Implement lock failure action in sanlock driver 2012-10-11 14:41:42 +02:00
lxc lxc: Correctly report active cgroups 2012-10-02 10:28:38 +02:00
network maint: drop spurious semicolons 2012-10-15 09:08:19 -06:00
node_device Change logging category parameter into an enum 2012-09-28 10:39:28 +01:00
nwfilter maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
openvz maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
parallels Use size_t instead of int for virDomainDefPtr struct 2012-09-27 10:11:44 +01:00
phyp maint: drop spurious semicolons 2012-10-15 09:08:19 -06:00
qemu maint: drop spurious semicolons 2012-10-15 09:08:19 -06:00
remote Add support for SUSPEND_DISK event 2012-10-15 12:09:10 +02:00
rpc Various typos and misspellings 2012-10-12 00:03:43 +02:00
secret maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
security selinux: Use raw contexts 2 2012-10-16 10:30:18 +02:00
storage selinux: Use raw contexts 2012-10-12 17:54:09 +02:00
test maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
uml Various typos and misspellings 2012-10-12 00:03:43 +02:00
util Introduce an internal API for handling file based lockspaces 2012-10-16 15:45:55 +01:00
vbox Various typos and misspellings 2012-10-12 00:03:43 +02:00
vmware maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
vmx Use size_t instead of int for virDomainDefPtr struct 2012-09-27 10:11:44 +01:00
xen Various typos and misspellings 2012-10-12 00:03:43 +02:00
xenapi Call curl_global_init from virInitialize to avoid thread-safety issues 2012-10-08 21:27:58 +02:00
xenxs Various typos and misspellings 2012-10-12 00:03:43 +02:00
check-symfile.pl Check for private symbols presence as well 2012-10-05 15:04:56 +02:00
datatypes.c maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
datatypes.h maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
driver.c maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
driver.h network: define new API virNetworkUpdate 2012-09-18 04:21:32 -04:00
dtrace2systemtap.pl maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
fdstream.c maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
fdstream.h maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
gnutls_1_0_compat.h maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
internal.h Various typos and misspellings 2012-10-12 00:03:43 +02:00
libvirt_atomic.syms Rewrite virAtomic APIs using GLib's atomic ops code 2012-08-02 11:50:59 +01:00
libvirt_daemon.syms
libvirt_driver_modules.syms Override default driver dir when running from GIT 2012-05-24 13:18:01 +01:00
libvirt_esx.syms Remove libvirt_test.la library 2012-05-24 13:18:00 +01:00
libvirt_internal.h maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
libvirt_libssh2.syms libssh2_transport: add main libssh2 transport implementation 2012-08-21 14:47:09 +02:00
libvirt_linux.syms build: Don't export xenLinuxDomainBlockStats symbol 2012-07-31 11:28:32 +02:00
libvirt_openvz.syms openvz: Add openvzVEGetStringParam 2012-07-20 21:54:35 +02:00
libvirt_private.syms Introduce an internal API for handling file based lockspaces 2012-10-16 15:45:55 +01:00
libvirt_probes.d Turn virNetClient* into virObject instances 2012-08-07 11:47:55 +01:00
libvirt_public.syms network: define new API virNetworkUpdate 2012-09-18 04:21:32 -04:00
libvirt_qemu_probes.d build: fix binary location in stap files --with-driver-modules 2012-08-10 23:11:26 -04:00
libvirt_qemu.syms qemu-agent: available in 0.10.0 2012-08-23 13:05:52 -06:00
libvirt_sasl.syms Move some SASL symbols into libvirt_sasl.syms 2012-08-15 21:41:42 +01:00
libvirt_vmx.syms
libvirt_xenxs.syms
libvirt-qemu.c maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
libvirt.c Various typos and misspellings 2012-10-12 00:03:43 +02:00
libvirt.conf Allow overriding default URI in config file 2012-03-15 11:20:17 +00:00
Makefile.am Introduce an internal API for handling file based lockspaces 2012-10-16 15:45:55 +01:00
nodeinfo.c node_memory: Add new parameter field to tune the new sysfs knob 2012-10-15 17:35:54 +08:00
nodeinfo.h maint: fix up copyright notice inconsistencies 2012-09-20 16:30:55 -06:00
qemu_protocol-structs agent: add remote driver support 2012-08-23 19:05:50 +08:00
README hyperv: Add basic documentation 2011-08-26 17:52:55 +02:00
remote_protocol-structs Add support for SUSPEND_DISK event 2012-10-15 12:09:10 +02:00
virkeepaliveprotocol-structs build: Properly generate and check virkeepaliveprotocol-structs 2011-11-24 14:44:04 +01:00
virnetprotocol-structs Extend RPC protocol to allow FD passing 2011-10-28 10:27:15 +01:00

       libvirt library code README
       ===========================

The directory provides the bulk of the libvirt codebase. Everything
except for the libvirtd daemon and client tools. The build uses a
large number of libtool convenience libraries - one for each child
directory, and then links them together for the final libvirt.so,
although some bits get linked directly to libvirtd daemon instead.

The files directly in this directory are supporting the public API
entry points & data structures.

There are two core shared modules to be aware of:

 * util/  - a collection of shared APIs that can be used by any
            code. This directory is always in the include path
            for all things built

 * conf/  - APIs for parsing / manipulating all the official XML
            files used by the public API. This directory is only
            in the include path for driver implementation modules

 * vmx/   - VMware VMX config handling (used by esx/ and vmware/)


Then there are the hypervisor implementations:

 * esx/          - VMware ESX and GSX support using vSphere API over SOAP
 * hyperv/       - Microsoft Hyper-V support using WinRM
 * lxc/          - Linux Native Containers
 * openvz/       - OpenVZ containers using cli tools
 * phyp/         - IBM Power Hypervisor using CLI tools over SSH
 * qemu/         - QEMU / KVM using qemu CLI/monitor
 * remote/       - Generic libvirt native RPC client
 * test/         - A "mock" driver for testing
 * uml/          - User Mode Linux
 * vbox/         - Virtual Box using native API
 * vmware/       - VMware Workstation and Player using the vmrun tool
 * xen/          - Xen using hypercalls, XenD SEXPR & XenStore
 * xenapi/       - Xen using libxenserver


Finally some secondary drivers that are shared for several HVs.
Currently these are used by LXC, OpenVZ, QEMU, UML and Xen drivers.
The ESX, Hyper-V, Power Hypervisor, Remote, Test & VirtualBox drivers all
implement the secondary drivers directly

 * cpu/          - CPU feature management
 * interface/    - Host network interface management
 * network/      - Virtual NAT networking
 * nwfilter/     - Network traffic filtering rules
 * node_device/  - Host device enumeration
 * secret/       - Secret management
 * security/     - Mandatory access control drivers
 * storage/      - Storage management drivers


Since both the hypervisor and secondary drivers can be built as
dlopen()able modules, it is *FORBIDDEN* to have build dependencies
between these directories. Drivers are only allowed to depend on
the public API, and the internal APIs in the util/ and conf/
directories