[Xen-devel] [PATCH] unnecessary removal of guest console characters

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

Hi all,
currently when max_capacity is set in xenconsoled and the buffer if 
completely filled then some characters in the buffer are discarded (even 
though the rate limitation makes this unlikely to happen).
A better way to handle this scenario would be to stop reading from the 
ring until the buffer has some free space.
I am attaching a simple patch that does exactly this.
Best Regards,

Stefano Stabellini

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff -r 082d3886fded tools/console/daemon/io.c
--- a/tools/console/daemon/io.c Fri Apr 11 09:14:03 2008 +0100
+++ b/tools/console/daemon/io.c Fri Apr 11 14:12:51 2008 +0100
@@ -200,21 +200,6 @@ static void buffer_append(struct domain 
                              "on domain %d: %d (%s)\n",
                              dom->domid, errno, strerror(errno));
        }
-
-       if (buffer->max_capacity &&
-           buffer->size > buffer->max_capacity) {
-               /* Discard the middle of the data. */
-
-               size_t over = buffer->size - buffer->max_capacity;
-               char *maxpos = buffer->data + buffer->max_capacity;
-
-               memmove(maxpos - over, maxpos, over);
-               buffer->data = realloc(buffer->data, buffer->max_capacity);
-               buffer->size = buffer->capacity = buffer->max_capacity;
-
-               if (buffer->consumed > buffer->max_capacity - over)
-                       buffer->consumed = buffer->max_capacity - over;
-       }
 }
 
 static bool buffer_empty(struct buffer *buffer)
@@ -228,6 +213,11 @@ static void buffer_advance(struct buffer
        if (buffer->consumed == buffer->size) {
                buffer->consumed = 0;
                buffer->size = 0;
+               if (buffer->max_capacity &&
+                   buffer->capacity > buffer->max_capacity) {
+                       buffer->data = realloc(buffer->data, 
buffer->max_capacity);
+                       buffer->capacity = buffer->max_capacity;
+               }
        }
 }
 
@@ -1005,9 +995,12 @@ void handle_io(void)
                                    d->next_period < next_timeout)
                                        next_timeout = d->next_period;
                        } else if (d->xce_handle != -1) {
-                               int evtchn_fd = xc_evtchn_fd(d->xce_handle);
-                               FD_SET(evtchn_fd, &readfds);
-                               max_fd = MAX(evtchn_fd, max_fd);
+                               if (!d->buffer.max_capacity ||
+                                   d->buffer.size < d->buffer.max_capacity) {
+                                       int evtchn_fd = 
xc_evtchn_fd(d->xce_handle);
+                                       FD_SET(evtchn_fd, &readfds);
+                                       max_fd = MAX(evtchn_fd, max_fd);
+                               }
                        }
 
                        if (d->master_fd != -1) {

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