On Wed, Jun 22, 2016 at 04:43:24PM +0200, Michal Privoznik wrote:
This API can be used to tell the other side of the stream to skip some bytes in the stream. This can be used to create a sparse file on the receiving side of a stream.
It takes just one argument @length, which says how big the hole is. Since our streams are not rewindable like regular files, we don't need @whence argument like seek(2) has.
Signed-off-by: Michal Privoznik <mprivozn@redhat.com> --- include/libvirt/libvirt-stream.h | 3 +++ src/driver-stream.h | 5 ++++ src/libvirt-stream.c | 57 ++++++++++++++++++++++++++++++++++++++++ src/libvirt_public.syms | 1 + 4 files changed, 66 insertions(+)
diff --git a/include/libvirt/libvirt-stream.h b/include/libvirt/libvirt-stream.h index bee2516..4e0a599 100644 --- a/include/libvirt/libvirt-stream.h +++ b/include/libvirt/libvirt-stream.h @@ -50,6 +50,9 @@ int virStreamRecvFlags(virStreamPtr st, size_t nbytes, unsigned int flags);
+int virStreamSkip(virStreamPtr st, + unsigned long long length); +
/** * virStreamSourceFunc: diff --git a/src/driver-stream.h b/src/driver-stream.h index d4b0480..20ea13f 100644 --- a/src/driver-stream.h +++ b/src/driver-stream.h @@ -42,6 +42,10 @@ typedef int unsigned int flags);
typedef int +(*virDrvStreamSkip)(virStreamPtr st, + unsigned long long length); + +typedef int (*virDrvStreamEventAddCallback)(virStreamPtr stream, int events, virStreamEventCallback cb, @@ -68,6 +72,7 @@ struct _virStreamDriver { virDrvStreamSend streamSend; virDrvStreamRecv streamRecv; virDrvStreamRecvFlags streamRecvFlags; + virDrvStreamSkip streamSkip; virDrvStreamEventAddCallback streamEventAddCallback; virDrvStreamEventUpdateCallback streamEventUpdateCallback; virDrvStreamEventRemoveCallback streamEventRemoveCallback; diff --git a/src/libvirt-stream.c b/src/libvirt-stream.c index 80b2d47..55f3ef5 100644 --- a/src/libvirt-stream.c +++ b/src/libvirt-stream.c @@ -346,6 +346,63 @@ virStreamRecvFlags(virStreamPtr stream,
/** + * virStreamSkip: + * @stream: pointer to the stream object + * @length: number of bytes to skip + * + * Skip @length bytes in the stream. This is useful when there's + * no actual data in the stream, just a hole. If that's the case, + * this API can be used to skip the hole properly instead of + * transmitting zeroes to the other side. + * + * An example using this with a hypothetical file upload API + * looks like: + * + * virStream st; + * + * while (1) { + * char buf[4096]; + * size_t len; + * if (..in hole...) { + * ..get hole size... + * virStreamSkip(st, len); + * } else { + * ...read len bytes... + * virStreamSend(st, buf, len); + * } + * } + * + * Returns 0 on success, + * -1 error + */ +int +virStreamSkip(virStreamPtr stream, + unsigned long long length) +{ + VIR_DEBUG("stream=%p, length=%llu", stream, length); + + virResetLastError(); + + virCheckStreamReturn(stream, -1); + + if (stream->driver && + stream->driver->streamSkip) { + int ret; + ret = (stream->driver->streamSkip)(stream, length); + if (ret < 0) + goto error; + return ret; + } + + virReportUnsupportedError(); + + error: + virDispatchError(stream->conn); + return -1; +} + + +/** * virStreamSendAll: * @stream: pointer to the stream object * @handler: source callback for reading data from application diff --git a/src/libvirt_public.syms b/src/libvirt_public.syms index d013d9f..5b536eb 100644 --- a/src/libvirt_public.syms +++ b/src/libvirt_public.syms @@ -739,6 +739,7 @@ LIBVIRT_2.0.0 { virDomainSetGuestVcpus; virConnectStoragePoolEventRegisterAny; virStreamRecvFlags; + virStreamSkip; } LIBVIRT_1.3.3;
We can put this in a 2.1.0 block now ACK Regards, Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :|