When one has a non-blocking stream and aborts or finishes it without
removing the callback, any event loop invocation will trigger that
callback, but it cannot be removed any more.  We cannot remove the
callback automatically from virStream{Abort,Finish} functions due to
forward-compatibility.  So let's at least document this behaviour,
because it is not easy to find out the reason for.
Signed-off-by: NMartin Kletzander <mkletzan@redhat.com>

There's a slight problem with the current function. Assume we are
currently in a data section and we have say 42 bytes until next
section. Therefore, just before (handler) is called to fill up
the buffer with data, @want is changed to 42 to match the amount
of data left in the current section. However, after hole is
processed, we are back in data section but with incredibly small
@want size. Nobody will ever reset it back. This results in
incredible data fragmentation.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

This is just an internal API, that calls corresponding function
in stream driver. This function will set @data = 1 if the
underlying file is in data section, or @data = 0 if it is in a
hole. At any rate, @length is set to number of bytes remaining in
the section the file currently is.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

This is just a wrapper over new function that have been just
introduced: virStreamSendHole() . It's very similar to
virStreamSendAll() except it handles sparse streams well.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

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: NMichal Privoznik <mprivozn@redhat.com>

Add a new flag to virStreamRecvFlags in order to handle being able to
stop reading from the stream so that the consumer can generate a "hole"
in stream target. Generation of a hole replaces the need to receive and
handle a sequence of zero bytes for sparse stream targets.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

This function is basically a counterpart for virStreamSendHole().
If one side of a stream called virStreamSendHole() the other
should call virStreamRecvHole() to get the size of the hole.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

This API is 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 @length argument, which says how big the hole is. This
skipping is done from the current point of stream. Since our
streams are not rewindable like regular files, we don't need
@whence argument like seek(2) has.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

This patch is adding the virStreamRecvFlags as a variant to the
virStreamRecv function in order to allow for future expansion of
functionality for processing sparse streams using a @flags
argument.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

These are wrappers over virStreamRecv and virStreamSend so that
users have to care about nothing but writing data into / reading
data from a sink (typically a file). Note, that these wrappers
are used exclusively on client side as the daemon has slightly
different approach. Anyway, the wrappers allocate this buffer and
use it for intermediate data storage until the data is passed to
stream to send, or to the client application. So far, we are
using 64KB buffer. This is enough, but suboptimal because server
can send messages up to VIR_NET_MESSAGE_LEGACY_PAYLOAD_MAX bytes
big (262120B, roughly 256KB). So if we make the buffer this big,
a single message containing the data is sent instead of four,
which is current situation. This means lower overhead, because
each message contains a header which needs to be processed, each
message is processed roughly same amount of time regardless of
its size, less bytes need to be sent through the wire, and so on.
Note that since server will never sent us a stream message bigger
than VIR_NET_MESSAGE_LEGACY_PAYLOAD_MAX there's no point in
sizing up the client buffer past this threshold.
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>

Introduce a src/libvirt-stream.c file to hold all the
methods related to the virStream type.