[libvirt] [PATCH 1/6] port allocator: make used port bitmap global

[Nikolay Shirokovskiy]

On 29.01.2018 09:09, Michal Privoznik wrote:
> On 12/20/2017 07:35 AM, Nikolay Shirokovskiy wrote:
>> Host tcp4/tcp6 ports is a global resource thus we need to make
>> port accounting also global or we have issues described in [1] when
>> port allocator ranges of different instances are overlapped (which
>> is by default for qemu for example).
>>
>> Let's have only one global port allocator object that take care
>> of the entire ports range (0 - 65535) and introduce port range object
>> for clients to specify desired auto allocation band.
>>
>> [1] https://www.redhat.com/archives/libvir-list/2017-December/msg00600.html
>> ---
>>  src/bhyve/bhyve_driver.c       |   4 +-
>>  src/bhyve/bhyve_utils.h        |   2 +-
>>  src/libvirt_private.syms       |   3 +-
>>  src/libxl/libxl_conf.c         |   8 +--
>>  src/libxl/libxl_conf.h         |   8 +--
>>  src/libxl/libxl_driver.c       |  18 +++---
>>  src/qemu/qemu_conf.h           |   6 +-
>>  src/qemu/qemu_driver.c         |  30 +++++-----
>>  src/util/virportallocator.c    | 125 ++++++++++++++++++++++++++++-------------
>>  src/util/virportallocator.h    |  20 ++++---
>>  tests/bhyvexml2argvtest.c      |   6 +-
>>  tests/libxlxml2domconfigtest.c |   8 +--
>>  tests/virportallocatortest.c   |  48 ++++++++++------
>>  13 files changed, 175 insertions(+), 111 deletions(-)
>>
> 
>> diff --git a/src/util/virportallocator.c b/src/util/virportallocator.c
>> index fcd4f74..cd64356 100644
>> --- a/src/util/virportallocator.c
>> +++ b/src/util/virportallocator.c
>> @@ -35,10 +35,14 @@
>>  
>>  #define VIR_FROM_THIS VIR_FROM_NONE
>>  
>> +typedef struct _virPortAllocator virPortAllocator;
>> +typedef virPortAllocator *virPortAllocatorPtr;
>>  struct _virPortAllocator {
>>      virObjectLockable parent;
>>      virBitmapPtr bitmap;
>> +};
>>  
>> +struct _virPortRange {
>>      char *name;
>>  
>>      unsigned short start;
>> @@ -48,6 +52,7 @@ struct _virPortAllocator {
>>  };
>>  
>>  static virClassPtr virPortAllocatorClass;
>> +static virPortAllocatorPtr virPortAllocatorInstance;
> 
> I wonder if this is the way to go. I mean, this virPortAllocatorInstance
> is going to be a global variable that will never be freed (even if we
> wanted to). I mean, if virPortRange had a pointer to virPortAllocator

Not sure why we need to free it. It is like global variables for classes,
we don't need to free them yet. As to libxlxml2domconfigtest it can be
fixed just like virportallocatortest by releasing all acquired ports.

> and ref/unref it in virPortRangeNew() and virPortRangeFree() then we're
> good. To break this down, leave the global variable, have
> virPortRangeNew() call:
> 
> virPortRangePtr
> virPortRangeNew(const char *name,
>                 unsigned short start,
>                 unsigned short end,
>                 unsigned int flags)
> {
> 
>   virPortAllocatorInitialize();
> 
>   range->pa = virObjectRef(virPortAllocatorInstance);
>   ...
> }
> 
> Also, virPortAllocatorDispose() would set the virPortAllocatorInstance
> pointer to NULL.

I think this won't work. virPortAllocatorInitialize will set ref to 1 on
behalf of virPortAllocatorInstance. So after you dispose all ranges you
still have this 1 ref and dispose will not be called. And I don't know how
to fix this approach because on this way we have to use virOnce somehow
to initialize virPortAllocatorInstance many times. Also it looks just 
not natural - after freeing all port ranges you destroy port allocator.
Client can use port range as a temporary construct just to acquire port.

> 
> This is also the root cause of libxlxml2domconfigtest failing for me. So
> even though you construct virPortRange fresh new for each
> testCompareXMLToDomConfig() run, the underlying virPortAllocatorInstance
> stays through different runs. So a port allocated in one run stays
> allocated in the second run too. Yeah, virPortAllocatorRelease() is
> never called from this test.

Sorry, I did not build with libxl driver and thus did not run this test.
I can fix it as virportallocatortest - by releasing all acquired ports.

Nikolay