[libvirt] [PATCH] add compress stream support

[Vasiliy Tolstov]

23 сент. 2015 г. 16:18 пользователь "Daniel P. Berrange" <
berrange at redhat.com> написал:
>
> On Wed, Sep 23, 2015 at 03:20:51PM +0300, Vasiliy Tolstov wrote:
> > 2015-09-23 14:54 GMT+03:00 Daniel P. Berrange <berrange at redhat.com>:
> > > How have you actually tested this in practice - your patch does
> > > not change any code to make use of this new feate. You're changing
> > > the public API which suggests you expect the client apps to use
> > > this when passing a virStreamPtr to the virStorageVolDownload
> > > method, but the stream client apps pass is not backed by a
> > > virFDStream object. Only libvirtd uses the virFDSteam objects
> > > and you've not changed anything to make use ot that. So this is
> > > all rather strange still. Can you more clearly state what you
> > > are expecting to do.
> >
> >
> > As i'm understand client create stream via virStreamNew , when user
> > invoke virStoreVolDownload this function use created stream.
> > If i'm correct, libvirt when read/write in
> > virStoreVolDownload/virStoreVolUpload uses fdstream functions
> > internally. So data compressed or decompressed.
> > Or when client create virStreamNew and pass it libvirt not always use
> > fdstream functions ?
>
> It is not quite that simple because we have a client/server architecture.
>
> So the client app creates a virStreamPtr. This is used by the remote
> driver, via a virNetClientStream object to tunnel data over the
> libvirtd connection.
>

So client can't say what stream libvirtd need to create for storage driver?

> The libvirtd daemon then creates another virStreamPtr object. This is
> used by the straoge driver, via the virFDStream object to fetch the
> data the client is requesting.
>
> So having the client app request compression on its virStreamPtr
> does not work, because that stream object is not the one used
> by the virFDStream code.
>
> An alternative approach would be to not try to change the stream API
> at all.
>
> Instead pass flags to the virStorageVolDownload/Upload functions,
> eg VIR_STORAGE_VOL_STREAM_COMPRESS_ZLIB. This flag would get passed
> across to the storage driver, which can then turn on compression in
> the virFDStream impl. This would require
>
>  - Add the enum flags to include/libvirt/libvirt-storage.h
>  - Add libarchive support to src/fdstream.c
>  - Handle the new flags in src/storage/storage_driver.c to
>    turn on the libarchive compression in fdsream.c
>
> Regards,
> Daniel
> --
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