Re: [libvirt] [PATCH v3 27/31] fdstream: Implement sparse stream

Basically, what is needed here is to introduce new message type for the messages passed between the event loop callbacks and the worker thread that does all the I/O. The idea is that instead of a queue of read buffers we will have a queue where "hole of size X" messages appear. That way the even loop callbacks can just

check the head of the queue and see if the worker thread is in data or a hole section and how long the section is. Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/storage/storage_util.c | 4 +- src/util/virfdstream.c | 239 ++++++++++++++++++++++++++++++++++++++++----- src/util/virfdstream.h | 1 + 3 files changed, 220 insertions(+), 24 deletions(-)

diff --git a/src/util/virfdstream.c b/src/util/virfdstream.c index 4b42939e7..ba209025a 100644 --- a/src/util/virfdstream.c +++ b/src/util/virfdstream.c

static ssize_t virFDStreamThreadDoRead(virFDStreamDataPtr fdst, + bool sparse, const int fdin, const int fdout, const char *fdinname, const char *fdoutname, + size_t *dataLen, size_t buflen) { virFDStreamMsgPtr msg = NULL; + int inData = 0; + long long sectionLen = 0; char *buf = NULL; ssize_t got; + if (sparse && *dataLen == 0) { + if (virFileInData(fdin, &inData, &sectionLen) < 0) + goto error; + + if (inData) + *dataLen = sectionLen; + } + if (VIR_ALLOC(msg) < 0) goto error; - if (VIR_ALLOC_N(buf, buflen) < 0) - goto error; - - if ((got = saferead(fdin, buf, buflen)) < 0) { - virReportSystemError(errno, - _("Unable to read %s"), - fdinname); - goto error; + if (sparse && *dataLen == 0) { + msg->type = VIR_FDSTREAM_MSG_TYPE_HOLE; + msg->stream.hole.len = sectionLen; + got = sectionLen; + + /* HACK. The message queue is one directional. So caller

+ * cannot make us skip the hole. Do that for them instead. */ + if (sectionLen && + lseek(fdin, sectionLen, SEEK_CUR) == (off_t) -1) { + virReportSystemError(errno, + _("unable to seek in %s"), + fdinname); + goto error; + }

+static int +virFDStreamSendHole(virStreamPtr st, + long long length, + unsigned int flags) +{ + virFDStreamDataPtr fdst = st->privateData; + virFDStreamMsgPtr msg = NULL; + off_t off; + int ret = -1; + + virCheckFlags(0, -1); + + virObjectLock(fdst); + if (fdst->length) { + if (length > fdst->length - fdst->offset) + length = fdst->length - fdst->offset; + fdst->offset += length; + } + + if (fdst->thread) { + /* Things are a bit complicated here. But bear with me. If FDStream is

+ * in a read mode, then if the message at the queue head is HOLE, just + * pop it. The thread has lseek()-ed anyway. If however, the FDStream

+ * is in write mode, then tell the thread to do the lseek() for us. + * Under no circumstances we can do the lseek() ourselves here. We + * might mess up file position for the thread. */ + if (fdst->threadDoRead) { + msg = fdst->msg; + if (msg->type != VIR_FDSTREAM_MSG_TYPE_HOLE) { + virReportError(VIR_ERR_INTERNAL_ERROR, "%s", + _("Invalid stream hole")); + goto cleanup; + } + + virFDStreamMsgQueuePop(fdst, fdst->fd, "pipe"); + } else { + if (VIR_ALLOC(msg) < 0) + goto cleanup; + + msg->type = VIR_FDSTREAM_MSG_TYPE_HOLE; + msg->stream.hole.len = length; + virFDStreamMsgQueuePush(fdst, msg, fdst->fd, "pipe"); + msg = NULL; + }