Re: [libvirt] [PATCH v2 06/38] virfdstream: Use messages instead of pipe

One big downside of using the pipe to transfer the data is that we can really transfer just bare data. No metadata can be carried through unless some formatted messages are introduced. That would be quite painful to achieve so let's use a message queue. It's fairly easy to exchange info between threads now that iohelper is no longer used. The reason why we cannot use the FD for plain files directly is that despite us setting noblock flag on the FD, any read()/write() blocks regardless (which is a show stopper since those parts of the code are run from the event loop) and poll() reports such FD as always readable/writable - even though the subsequent operation might block. The pipe is still not gone though. It is used to signal to even loop that an event occurred (e.g. data are available for reading in the queue, or vice versa). Signed-off-by: Michal Privoznik <mprivozn(a)redhat.com&gt; --- src/util/virfdstream.c | 402 ++++++++++++++++++++++++++++++++++++++++++------- 1 file changed, 350 insertions(+), 52 deletions(-)

+static int +virFDStreamMsgQueuePush(virFDStreamDataPtr fdst, + virFDStreamMsgPtr msg, + int fd, + const char *fdname) +{ + virFDStreamMsgPtr *tmp = &fdst->msg; + char c = '1'; + + while (*tmp) + tmp = &(*tmp)->next; + + *tmp = msg; + virCondSignal(&fdst->threadCond); + + if (safewrite(fd, &c, sizeof(c)) != sizeof(c)) { + virReportSystemError(errno, + _("Unable to write to %s"), + fdname); + return -1; + } + + return 0; +} + + +static virFDStreamMsgPtr +virFDStreamMsgQueuePop(virFDStreamDataPtr fdst, + int fd, + const char *fdname) +{ + virFDStreamMsgPtr tmp = fdst->msg; + char c; + + if (tmp) { + fdst->msg = tmp->next; + tmp->next = NULL; + } + + virCondSignal(&fdst->threadCond); + + if (saferead(fd, &c, sizeof(c)) != sizeof(c)) { + virReportSystemError(errno, + _("Unable to read from %s"), + fdname); + return NULL; + } + + return tmp; +}

+static ssize_t +virFDStreamThreadDoRead(virFDStreamDataPtr fdst, + const int fdin, + const int fdout, + const char *fdinname, + const char *fdoutname, + size_t buflen) +{ + virFDStreamMsgPtr msg = NULL; + char *buf = NULL; + ssize_t got; + + 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; + } + + msg->type = VIR_FDSTREAM_MSG_TYPE_DATA; + msg->stream.data.buf = buf; + msg->stream.data.len = got; + buf = NULL; + + virFDStreamMsgQueuePush(fdst, msg, fdout, fdoutname); + msg = NULL; + + return got; + + error: + VIR_FREE(buf); + virFDStreamMsgFree(msg); + return -1; +} + + +static ssize_t +virFDStreamThreadDoWrite(virFDStreamDataPtr fdst, + const int fdin, + const int fdout, + const char *fdinname, + const char *fdoutname) +{ + ssize_t got; + virFDStreamMsgPtr msg = fdst->msg; + bool pop = false; + + switch (msg->type) { + case VIR_FDSTREAM_MSG_TYPE_DATA: + got = safewrite(fdout, + msg->stream.data.buf + msg->stream.data.offset, + msg->stream.data.len - msg->stream.data.offset); + if (got < 0) { + virReportSystemError(errno, + _("Unable to write %s"), + fdoutname); + return -1; + } + + msg->stream.data.offset += got; + + pop = msg->stream.data.offset == msg->stream.data.len; + break; + } + + if (pop) { + virFDStreamMsgQueuePop(fdst, fdin, fdinname); + virFDStreamMsgFree(msg); + } + + return got; +}

@@ -304,14 +496,12 @@ virFDStreamThread(void *opaque) int fdout = data->fdout; char *fdoutname = data->fdoutname; virFDStreamDataPtr fdst = st->privateData; - char *buf = NULL; + bool doRead = fdst->threadDoRead; size_t buflen = 256 * 1024; size_t total = 0; virObjectRef(fdst); - - if (VIR_ALLOC_N(buf, buflen) < 0) - goto error; + virObjectLock(fdst); while (1) { ssize_t got; @@ -323,39 +513,56 @@ virFDStreamThread(void *opaque) if (buflen == 0) break; /* End of requested data from client */ - if ((got = saferead(fdin, buf, buflen)) < 0) { - virReportSystemError(errno, - _("Unable to read %s"), - fdinname); + while (doRead == (fdst->msg != NULL) && + !fdst->threadQuit) { + if (virCondWait(&fdst->threadCond, &fdst->parent.lock)) { + virReportSystemError(errno, "%s", + _("failed to wait on condition")); + goto error; + } + } + + if (fdst->threadQuit) { + /* If stream abort was requested, quit early. */ + if (fdst->threadAbort) + goto cleanup; + + /* Otherwise flush buffers and quit gracefully. */ + if (doRead == (fdst->msg != NULL)) + break; + } + + if (doRead) + got = virFDStreamThreadDoRead(fdst, + fdin, fdout, + fdinname, fdoutname, + buflen); + else + got = virFDStreamThreadDoWrite(fdst, + fdin, fdout, + fdinname, fdoutname); + + if (got < 0)