[PATCH v5 03/15] libxl_qmp: Implement fd callback and read data

[Anthony PERARD <anthony.perard@citrix.com>]

First step into taking care of the input from QEMU's QMP socket. For
now, we read data and store them in a buffer.

Parsing of the data will be done in the following patches.

Signed-off-by: Anthony PERARD <anthony.perard@citrix.com>
---

Notes:
    v5:
        some cleanup
        remove read loop that only handled EINTR, simply return
    
    v4:
        remove use of a linked list of receive buffer, and use realloc instead.

 tools/libxl/libxl_internal.h |  8 +++
 tools/libxl/libxl_qmp.c      | 95 ++++++++++++++++++++++++++++++++++++
 2 files changed, 103 insertions(+)

diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index 9bcab39f00..0590801b30 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -439,6 +439,14 @@ struct libxl__ev_qmp {
     libxl__carefd *qmp_cfd;
     libxl__ev_fd qmp_efd;
     libxl__qmp_state qmp_state;
+    /* receive buffer, with:
+     * buf_size: current allocated size,
+     * buf_used: actual data in the buffer,
+     * buf_consumed: data already parsed.  */
+    char *rx_buf;
+    size_t buf_size;
+    size_t buf_used;
+    size_t buf_consumed;
 };
 
 
diff --git a/tools/libxl/libxl_qmp.c b/tools/libxl/libxl_qmp.c
index 167829a5ec..9ea303edf0 100644
--- a/tools/libxl/libxl_qmp.c
+++ b/tools/libxl/libxl_qmp.c
@@ -75,6 +75,12 @@
 #  define DEBUG_REPORT_RECEIVED(dom, buf, len) ((void)0)
 #endif
 
+#ifdef DEBUG_QMP_CLIENT
+#  define LOG_QMP(f, ...) LOGD(DEBUG, ev->domid, f, ##__VA_ARGS__)
+#else
+#  define LOG_QMP(f, ...)
+#endif
+
 /*
  * QMP types & constant
  */
@@ -1282,9 +1288,94 @@ int libxl__qmp_initializations(libxl__gc *gc, uint32_t domid,
 
 /* ------------ Implementation of libxl__ev_qmp ---------------- */
 
+/*
+ * QMP FD callbacks
+ */
+
+static int qmp_ev_callback_readable(libxl__egc *egc, libxl__ev_qmp *ev, int fd)
+{
+    EGC_GC;
+    ssize_t r;
+
+    if (!ev->rx_buf) {
+        ev->rx_buf = libxl__malloc(NOGC, QMP_RECEIVE_BUFFER_SIZE);
+        ev->buf_size = QMP_RECEIVE_BUFFER_SIZE;
+        ev->buf_used = 0;
+        ev->buf_consumed = 0;
+    }
+
+    /* Check if last buffer still have space, or increase size */
+    /* The -1 is because there is always space for a NUL character */
+    if (ev->buf_used == ev->buf_size - 1) {
+        ev->buf_size += QMP_RECEIVE_BUFFER_SIZE;
+        ev->rx_buf = libxl__realloc(NOGC, ev->rx_buf, ev->buf_size);
+    }
+
+    /* The -1 is because there is always space for a NUL character */
+    r = read(fd, ev->rx_buf + ev->buf_used, ev->buf_size - ev->buf_used - 1);
+    if (r < 0) {
+        if (errno == EINTR)
+            return 0;
+        assert(errno);
+        if (errno == EWOULDBLOCK)
+            return 0;
+        LOGED(ERROR, ev->domid, "error reading QMP socket");
+        return ERROR_FAIL;
+    }
+
+    if (r == 0) {
+        LOGD(ERROR, ev->domid, "No data read on QMP socket");
+        return 0;
+    }
+
+    LOG_QMP("received %ldB: '%.*s'", r, (int)r, ev->rx_buf + ev->buf_used);
+
+    ev->buf_used += r;
+    assert(ev->buf_used < ev->buf_size);
+
+    return 0;
+}
+
+static void qmp_ev_callback_error(libxl__egc *egc, libxl__ev_qmp *ev)
+{
+    EGC_GC;
+
+    LOGD(ERROR, ev->domid, "Error happend with the QMP connection to QEMU");
+
+    /* On error, deallocate all private ressources */
+    libxl__ev_qmp_dispose(gc, ev);
+}
+
 static void qmp_ev_fd_callback(libxl__egc *egc, libxl__ev_fd *ev_fd,
                                int fd, short events, short revents)
 {
+    EGC_GC;
+    int rc;
+
+    libxl__ev_qmp *ev = CONTAINER_OF(ev_fd, *ev, qmp_efd);
+
+    if (revents & (POLLHUP)) {
+        LOGD(DEBUG, ev->domid, "received POLLHUP from QMP socket");
+        rc = ERROR_FAIL;
+        goto out;
+    }
+    if (revents & ~(POLLIN|POLLOUT)) {
+        LOGD(ERROR, ev->domid,
+             "unexpected poll event 0x%x on QMP socket (expected POLLIN "
+             "and/or POLLOUT)",
+            revents);
+        rc = ERROR_FAIL;
+        goto out;
+    }
+
+    if (revents & POLLIN) {
+        rc = qmp_ev_callback_readable(egc, ev, fd);
+        if (rc)
+            goto out;
+    }
+out:
+    if (rc)
+        qmp_ev_callback_error(egc, ev);
 }
 
 static int qmp_ev_connect(libxl__gc *gc, libxl__ev_qmp *ev)
@@ -1350,6 +1441,8 @@ void libxl__ev_qmp_init(libxl__ev_qmp *ev)
     ev->qmp_cfd = NULL;
     libxl__ev_fd_init(&ev->qmp_efd);
     ev->qmp_state = qmp_state_disconnected;
+
+    ev->rx_buf = NULL;
 }
 
 int libxl__ev_qmp_send(libxl__gc *gc, libxl__ev_qmp *ev,
@@ -1365,6 +1458,8 @@ void libxl__ev_qmp_dispose(libxl__gc *gc, libxl__ev_qmp *ev)
 {
     LOGD(DEBUG, ev->domid, " ev %p", ev);
 
+    free(ev->rx_buf);
+
     libxl__ev_fd_deregister(gc, &ev->qmp_efd);
     libxl__carefd_close(ev->qmp_cfd);
 
-- 
Anthony PERARD


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