[libvirt] [PATCH 01/12] qemu: Add a hash table for the shared disks

[Osier Yang]

On 2012年12月13日 19:05, Jiri Denemark wrote:
> On Tue, Dec 11, 2012 at 21:37:18 +0800, Osier Yang wrote:
>> This introduces a hash table for qemu driver, to store the shared
>> disk's info as (@disk_path, {@ref_count, @orig_cdbfilter}). @ref_count
>> is the number of domains which shares the disk. @orig_cdbfilter is
>> the original cdbfilter setting of the shared disk, it will be used
>> to restore the the disk's cdbfilter setting to original value by
>> later patches.
>>
>> * src/qemu/qemu_conf.h: (Add member 'sharedDisks' of type
>>                           virHashTablePtr; New struct qemuSharedDiskEntry;
>>                           Declare helpers qemuAddSharedDisk,
>>                           qemuRemoveSharedDisk)
>> * src/qemu/qemu_conf.c (Implement the two helpers)
>> * src/qemu/qemu_process.c (Update 'sharedDisks' when domain
>>                             starting and shutdown)
>> * src/qemu/qemu_driver.c (Update 'sharedDisks' when attaching
>>                            or detaching disk).
>>
>> 0 is passed for orig_cdbfilter temporarily, later patches will update
>> it.
>> ---
>>   src/qemu/qemu_conf.c    |   48 +++++++++++++++++++++++++++++++++++++++++++++++
>>   src/qemu/qemu_conf.h    |   18 +++++++++++++++++
>>   src/qemu/qemu_driver.c  |   17 ++++++++++++++++
>>   src/qemu/qemu_process.c |   17 +++++++++++++++-
>>   4 files changed, 99 insertions(+), 1 deletions(-)
>>
>> diff --git a/src/qemu/qemu_conf.c b/src/qemu/qemu_conf.c
>> index 8d380a1..2b21186 100644
>> --- a/src/qemu/qemu_conf.c
>> +++ b/src/qemu/qemu_conf.c
>> @@ -556,3 +556,51 @@ qemuDriverCloseCallbackRunAll(virQEMUDriverPtr driver,
>>
>>       virHashForEach(driver->closeCallbacks, qemuDriverCloseCallbackRun,&data);
>>   }
>> +
>> +/* Increase ref count if the entry already exists, otherwise
>> + * add a new entry.
>> + */
>> +int
>> +qemuAddSharedDisk(virHashTablePtr sharedDisks,
>> +                  const char *disk_path,
>> +                  int orig_cdbfilter)
>> +{
>> +    qemuSharedDiskEntryPtr entry = NULL;
>> +
>> +    if ((entry = virHashLookup(sharedDisks, disk_path))) {
>> +        entry->ref++;
>> +    } else {
>> +        if (VIR_ALLOC(entry)<  0)
>> +            return -1;
>> +
>> +        entry->ref = 1;
>> +        entry->orig_cdbfilter = orig_cdbfilter;
>> +
>> +        if (virHashAddEntry(sharedDisks, disk_path, entry))
>> +            return -1;
>> +    }
>
> In addition to Daniel's comments, I think this hash table should contain
> device number rather than disk path since /dev is full of symlinks. One
> domain may be configured to use /dev/sdg while another one would use
> /dev/disk/by-id/..., another one /dev/disk/by-uuid/... and they can all
> lead to the same block device. Thus you need to canonicalize disk_path
> first, e.g., into major:minor and store that in the hash table.
>

Hum, agreed, this is really good catch which saves us from the
potential bug. Thanks.

Regards,
Osier