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Re: [libvirt] [PATCH v3 08/31] Introduce virStreamSparseRecvAll




On 05/17/2017 08:40 AM, Michal Privoznik wrote:
> On 05/16/2017 11:34 PM, John Ferlan wrote:
>>
>>
>> On 05/16/2017 10:03 AM, Michal Privoznik wrote:
>>> This is just a wrapper over new functions that have been just
>>> introduced: virStreamRecvFlags(), virStreamRecvHole(). It's very
>>> similar to virStreamRecvAll() except it handles sparse streams
>>> well.
>>>
>>> Signed-off-by: Michal Privoznik <mprivozn redhat com>
>>> ---
>>>  include/libvirt/libvirt-stream.h |  33 ++++++++++-
>>>  src/libvirt-stream.c             | 123 +++++++++++++++++++++++++++++++++++++++
>>>  src/libvirt_public.syms          |   1 +
>>>  3 files changed, 154 insertions(+), 3 deletions(-)
>>>
>>
>> [...]
>>
>>> diff --git a/src/libvirt-stream.c b/src/libvirt-stream.c
>>> index bedb6159a..6bf4c4f29 100644
>>> --- a/src/libvirt-stream.c
>>> +++ b/src/libvirt-stream.c
>>> @@ -668,6 +668,129 @@ virStreamRecvAll(virStreamPtr stream,
>>>  }
>>>  
>>>  
>>> +/**
>>> + * virStreamSparseRecvAll:
>>> + * @stream: pointer to the stream object
>>> + * @handler: sink callback for writing data to application
>>> + * @holeHandler: stream hole callback for skipping holes
>>> + * @opaque: application defined data
>>> + *
>>> + * Receive the entire data stream, sending the data to the
>>> + * requested data sink @handler and calling the skip @holeHandler
>>> + * to generate holes for sparse stream targets. This is simply a
>>> + * convenient alternative to virStreamRecvFlags, for apps that do
>>> + * blocking-I/O.
>>> + *
>>> + * An example using this with a hypothetical file download
>>> + * API looks like:
>>> + *
>>> + *   int mysink(virStreamPtr st, const char *buf, int nbytes, void *opaque) {
>>> + *       int *fd = opaque;
>>> + *
>>> + *       return write(*fd, buf, nbytes);
>>> + *   }
>>> + *
>>> + *   int myskip(virStreamPtr st, long long offset, void *opaque) {
>>> + *       int *fd = opaque;
>>> + *
>>
>> I think this is where perhaps the example of lseek in "off_t" chunks of
>> "long long offset" would be applicable...  Perhaps why I ended up in the
>> off_t rathole before.
> 
> Not sure what you mean. long long is the same size as off_t for any
> application that enables large file support (libvirt does that) or is
> compiled on 64bits. Any 32bit virt mgmt application should really enable
> large file support, otherwise is pretty useless.
> 
It's that off_t as 4 signed on 32 bit that I keep thinking/wondering
about... Still that's a special case for that and I agree beyond the
worry of what is being done here.

John
>>
>>> + *       return lseek(*fd, offset, SEEK_CUR) == (off_t) -1 ? -1 : 0;
>>> + *   }
>>> + *
>>> + *   virStreamPtr st = virStreamNew(conn, 0);
>>> + *   int fd = open("demo.iso", O_WRONLY);
>>> + *
>>> + *   virConnectDownloadSparseFile(conn, st);
>>
>> ^^ This API doesn't exist...  Of course neither did
>> virConnectDownloadFile from whence you copied the example.  Maybe both
>> should be 'adjusted'.
> 
> Maybe. One day. For now I'm happy with this example as-is. The example
> should show how to set up virStreamSparseRecvAll.
> 
> Michal
> 


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