Module libvirt-stream from libvirt

Request that the in progress data transfer be cancelled abnormally before the end of the stream has been reached. For output streams this can be used to inform the driver that the stream is being terminated early. For input streams this can be used to inform the driver that it should stop sending data.

If the stream is non-blocking, any callback must be removed beforehand.

Register a callback to be notified when a stream becomes writable, or readable. This is most commonly used in conjunction with non-blocking data streams to integrate into an event loop

Callback for receiving stream events. The callback will be invoked once for each event which is pending.

Remove an event callback from the stream

Changes the set of events to monitor for a stream. This allows for event notification to be changed without having to unregister & register the callback completely. This method is guaranteed to succeed if a callback is already registered

Indicate that there is no further data to be transmitted on the stream. For output streams this should be called once all data has been written. For input streams this should be called once virStreamRecv returns end-of-file.

This method is a synchronization point for all asynchronous errors, so if this returns a success code the application can be sure that all data has been successfully processed.

If the stream is non-blocking, any callback must be removed beforehand.

Decrement the reference count on a stream, releasing the stream object if the reference count has hit zero.

There must not be an active data transfer in progress when releasing the stream. If a stream needs to be disposed of prior to end of stream being reached, then the virStreamAbort function should be called first.

Creates a new stream object which can be used to perform streamed I/O with other public API function.

When no longer needed, a stream object must be released with virStreamFree. If a data stream has been used, then the application must call virStreamFinish or virStreamAbort before free'ing to, in order to notify the driver of termination.

If a non-blocking data stream is required passed VIR_STREAM_NONBLOCK for flags, otherwise pass 0.

Reads a series of bytes from the stream. This method may block the calling application for an arbitrary amount of time.

Errors are not guaranteed to be reported synchronously with the call, but may instead be delayed until a subsequent call.

An example using this with a hypothetical file download API looks like

  virStreamPtr st = virStreamNew(conn, 0);
  int fd = open("demo.iso", O_WRONLY, 0600);

  virConnectDownloadFile(conn, "demo.iso", st);

  while (1) {
      char buf[1024];
      int got = virStreamRecv(st, buf, 1024);
      if (got < 0) {
         virStreamAbort(st);
         break;
      }
      if (got == 0) {
         virStreamFinish(st);
         break;
      }
      int offset = 0;
      while (offset < got) {
         int sent = write(fd, buf + offset, got - offset);
         if (sent < 0) {
            virStreamAbort(st);
            goto done;
         }
         offset += sent;
      }
  }
  if (virStreamFinish(st) < 0)
     ... report an error ....
done:
  virStreamFree(st);
  close(fd);

Receive the entire data stream, sending the data to the requested data sink. This is simply a convenient alternative to virStreamRecv, 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);
}

virStreamPtr st = virStreamNew(conn, 0);
int fd = open("demo.iso", O_WRONLY);

virConnectUploadFile(conn, st);
if (virStreamRecvAll(st, mysink, &fd) < 0) {
   ...report an error ...
   goto done;
}
if (virStreamFinish(st) < 0)
   ...report an error...
virStreamFree(st);
close(fd);

Reads a series of bytes from the stream. This method may block the calling application for an arbitrary amount of time.

This is just like virStreamRecv except this one has extra flags. Calling this function with no flags set (equal to zero) is equivalent to calling virStreamRecv(stream, data, nbytes).

If flag VIR_STREAM_RECV_STOP_AT_HOLE is set, this function will stop reading from stream if it has reached a hole. In that case, -3 is returned and virStreamRecvHole() should be called to get the hole size. An example using this flag might look like this:

while (1) {
  char buf[4096];

  int ret = virStreamRecvFlags(st, buf, len, VIR_STREAM_STOP_AT_HOLE);
  if (ret < 0) {
    if (ret == -3) {
      long long len;
      ret = virStreamRecvHole(st, &len, 0);
      if (ret < 0) {
        ...error..
      } else {
        ...seek len bytes in target...
      }
    } else {
      return -1;
    }
  } else {
      ...write buf to target...
  }
}

This API is used to determine the length in bytes of the empty space to be created in a stream's target file when uploading or downloading sparsely populated files. This is the counterpart to virStreamSendHole().

Increment the reference count on the stream. For each additional call to this method, there shall be a corresponding call to virStreamFree to release the reference count, once the caller no longer needs the reference to this object.

Write a series of bytes to the stream. This method may block the calling application for an arbitrary amount of time. Once an application has finished sending data it should call virStreamFinish to wait for successful confirmation from the driver, or detect any error.

This method may not be used if a stream source has been registered.

Errors are not guaranteed to be reported synchronously with the call, but may instead be delayed until a subsequent call.

An example using this with a hypothetical file upload API looks like

  virStreamPtr st = virStreamNew(conn, 0);
  int fd = open("demo.iso", O_RDONLY);

  virConnectUploadFile(conn, "demo.iso", st);

  while (1) {
       char buf[1024];
       int got = read(fd, buf, 1024);
       if (got < 0) {
          virStreamAbort(st);
          break;
       }
       if (got == 0) {
          virStreamFinish(st);
          break;
       }
       int offset = 0;
       while (offset < got) {
          int sent = virStreamSend(st, buf+offset, got-offset);
          if (sent < 0) {
             virStreamAbort(st);
             goto done;
          }
          offset += sent;
       }
   }
   if (virStreamFinish(st) < 0)
      ... report an error ....
 done:
   virStreamFree(st);
   close(fd);

Send the entire data stream, reading the data from the requested data source. This is simply a convenient alternative to virStreamSend, for apps that do blocking-I/O.

An example using this with a hypothetical file upload API looks like

int mysource(virStreamPtr st, char *buf, int nbytes, void *opaque) {
    int *fd = opaque;

    return read(*fd, buf, nbytes);
}

virStreamPtr st = virStreamNew(conn, 0);
int fd = open("demo.iso", O_RDONLY);

virConnectUploadFile(conn, st);
if (virStreamSendAll(st, mysource, &fd) < 0) {
   ...report an error ...
   goto done;
}
if (virStreamFinish(st) < 0)
   ...report an error...
virStreamFree(st);
close(fd);

Rather than transmitting empty file space, this API directs the stream target to create length bytes of empty space. This API would be used when uploading or downloading sparsely populated files to avoid the needless copy of empty file space.

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...
    virStreamSendHole(st, len, 0);
  } else {
    ...read len bytes...
    virStreamSend(st, buf, len);
  }
}

The virStreamSinkFunc callback is used together with the virStreamRecvAll or virStreamSparseRecvAll functions for libvirt to provide the data that has been received.

The callback will be invoked multiple times, providing data in small chunks. The application should consume up 'nbytes' from the 'data' array of data and then return the number actual number of bytes consumed. The callback will continue to be invoked until it indicates the end of the stream has been reached. A return value of -1 at any time will abort the receive operation

Please note that for more accurate error reporting the callback should set appropriate errno on failure.

This callback is used together with the virStreamSparseRecvAll function for libvirt to provide the size of a hole that occurred in the stream.

The callback may be invoked multiple times as holes are found during processing a stream. The application should create the hole in the stream target and then return. A return value of -1 at any time will abort the receive operation.

Please note that for more accurate error reporting the callback should set appropriate errno on failure.

The virStreamSourceFunc callback is used together with the virStreamSendAll and virStreamSparseSendAll functions for libvirt to obtain the data that is to be sent.

The callback will be invoked multiple times, fetching data in small chunks. The application should fill the 'data' array with up to 'nbytes' of data and then return the number actual number of bytes. The callback will continue to be invoked until it indicates the end of the source has been reached by returning 0. A return value of -1 at any time will abort the send operation.

Please note that for more accurate error reporting the callback should set appropriate errno on failure.

The virStreamSourceHoleFunc callback is used together with the virStreamSparseSendAll function for libvirt to obtain the length of section stream is currently in.

Moreover, upon successful return, length should be updated with how many bytes are left until the current section ends (either data section or hole section). Also the stream is currently in data section, inData should be set to a non-zero value and vice versa.

NB: there's an implicit hole at the end of each file. If that's the case, inData and length should be both set to 0.

This function should not adjust the current position within the file.

Please note that for more accurate error reporting the callback should set appropriate errno on failure.

This callback is used together with the virStreamSparseSendAll to skip holes in the underlying file as reported by virStreamSourceHoleFunc.

The callback may be invoked multiple times as holes are found during processing a stream. The application should skip processing the hole in the stream source and then return. A return value of -1 at any time will abort the send operation.

Please note that for more accurate error reporting the callback should set appropriate errno on failure.

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;

    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);
if (virStreamSparseRecvAll(st, mysink, myskip, &fd) < 0) {
   ...report an error ...
   goto done;
}
if (virStreamFinish(st) < 0)
   ...report an error...
virStreamFree(st);
close(fd);

Note that opaque data is shared between both handler and holeHandler callbacks.

Send the entire data stream, reading the data from the requested data source. This is simply a convenient alternative to virStreamSend, for apps that do blocking-I/O.

An example using this with a hypothetical file upload API looks like

int mysource(virStreamPtr st, char *buf, int nbytes, void *opaque) {
    int *fd = opaque;

    return read(*fd, buf, nbytes);
}

int myskip(virStreamPtr st, long long offset, void *opaque) {
    int *fd = opaque;

    return lseek(*fd, offset, SEEK_CUR) == (off_t) -1 ? -1 : 0;
}

int myindata(virStreamPtr st, int *inData,
             long long *offset, void *opaque) {
    int *fd = opaque;

    if (@fd in hole) {
        *inData = 0;
        *offset = holeSize;
    } else {
        *inData = 1;
        *offset = dataSize;
    }

    return 0;
}

virStreamPtr st = virStreamNew(conn, 0);
int fd = open("demo.iso", O_RDONLY);

virConnectUploadSparseFile(conn, st);
if (virStreamSparseSendAll(st,
                           mysource,
                           myindata,
                           myskip,
                           &fd) < 0) {
   ...report an error ...
   goto done;
}
if (virStreamFinish(st) < 0)
   ...report an error...
virStreamFree(st);
close(fd);

Note that opaque data are shared between handler, holeHandler and skipHandler.