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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> |
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.. | ||
conf | ||
cpu | ||
esx | ||
hyperv | ||
interface | ||
libxl | ||
locking | ||
lxc | ||
network | ||
node_device | ||
nwfilter | ||
openvz | ||
parallels | ||
phyp | ||
qemu | ||
remote | ||
rpc | ||
secret | ||
security | ||
storage | ||
test | ||
uml | ||
util | ||
vbox | ||
vmware | ||
vmx | ||
xen | ||
xenapi | ||
xenxs | ||
check-symfile.pl | ||
datatypes.c | ||
datatypes.h | ||
driver.c | ||
driver.h | ||
dtrace2systemtap.pl | ||
fdstream.c | ||
fdstream.h | ||
gnutls_1_0_compat.h | ||
internal.h | ||
libvirt_atomic.syms | ||
libvirt_daemon.syms | ||
libvirt_driver_modules.syms | ||
libvirt_esx.syms | ||
libvirt_internal.h | ||
libvirt_libssh2.syms | ||
libvirt_linux.syms | ||
libvirt_openvz.syms | ||
libvirt_private.syms | ||
libvirt_probes.d | ||
libvirt_public.syms | ||
libvirt_qemu_probes.d | ||
libvirt_qemu.syms | ||
libvirt_sasl.syms | ||
libvirt_vmx.syms | ||
libvirt_xenxs.syms | ||
libvirt-qemu.c | ||
libvirt.c | ||
libvirt.conf | ||
Makefile.am | ||
nodeinfo.c | ||
nodeinfo.h | ||
qemu_protocol-structs | ||
README | ||
remote_protocol-structs | ||
virkeepaliveprotocol-structs | ||
virnetprotocol-structs |
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