The internal representation of a JSON array counts the items in
size_t. However, for some reason, when asking for the count it's
reported as int. Firstly, we need the function to return a signed
type as it's returning -1 on an error. But, not every system has
integer the same size as size_t. Therefore, lets return ssize_t.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Any source file which calls the logging APIs now needs
to have a VIR_LOG_INIT("source.name") declaration at
the start of the file. This provides a static variable
of the virLogSource type.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Our current pidfile acquire APis (virPidFileAcquire) simply return -1 upon
failure to acquire a lock. This patch adds a parameter 'bool waitForLock'
which instructs the APIs if we want to make it block and wait for the lock
or not.
Normally a lockspace resource is not freed while there are
active owners. During initial resource creation though, an
OOM error will trigger this scenario. virLockSpaceResourceFree
was not freeing the 'owners' field in this case.
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
The source code base needs to be adapted as well. Some files
include virutil.h just for the string related functions (here,
the include is substituted to match the new file), some include
virutil.h without any need (here, the include is removed), and
some require both.
The "restart" function for locks allocates a new array according to
and pre-sets its length, then reads the owner pids from a JSON
document in a loop. Rather than adding each owner at a different
index, though, it repeatedly overwrites the last element of the array
with all the owners.
Add two new APIs virLockSpaceNewPostExecRestart and
virLockSpacePreExecRestart which allow a virLockSpacePtr
object to be created from a JSON object and saved to a
JSON object, for the purposes of re-exec'ing a process.
As well as saving the state in JSON format, the second
method will disable the O_CLOEXEC flag so that the open
file descriptors are preserved across the process re-exec()
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
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>
