[Qemu-devel] [6701] char-mux: Use separate input buffers (Jan Kiszka)

[Qemu-devel] [6701] char-mux: Use separate input buffers (Jan Kiszka)

[Anthony Liguori]

Revision: 6701
          http://svn.sv.gnu.org/viewvc/?view=rev&root=qemu&revision=6701
Author:   aliguori
Date:     2009-03-05 23:00:02 +0000 (Thu, 05 Mar 2009)
Log Message:
-----------
char-mux: Use separate input buffers (Jan Kiszka)

Currently, the intermediate input buffer of mux'ed character devices
records data across all sub-devices. This has the side effect that we
easily leak data recorded over one sub-devices to another once we switch
the focus. Avoid data loss and confusion by defining exclusive buffers.

Note: In contrast to the original author's claim, the buffering concept
still breaks down when the fifo of the currently active sub-device is
full. As we cannot accept futher data from this point on without risking
to loose it, we will also miss escape sequences, just like without all
that buffering. In short: There is no reliable escape sequence handling
without infinite buffers or the risk of loosing some data.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

Modified Paths:
--------------
    trunk/qemu-char.c

Modified: trunk/qemu-char.c
===================================================================
--- trunk/qemu-char.c	2009-03-05 22:59:58 UTC (rev 6700)
+++ trunk/qemu-char.c	2009-03-05 23:00:02 UTC (rev 6701)
@@ -225,12 +225,15 @@
     IOEventHandler *chr_event[MAX_MUX];
     void *ext_opaque[MAX_MUX];
     CharDriverState *drv;
-    unsigned char buffer[MUX_BUFFER_SIZE];
-    int prod;
-    int cons;
     int mux_cnt;
     int term_got_escape;
     int max_size;
+    /* Intermediate input buffer allows to catch escape sequences even if the
+       currently active device is not accepting any input - but only until it
+       is full as well. */
+    unsigned char buffer[MAX_MUX][MUX_BUFFER_SIZE];
+    int prod[MAX_MUX];
+    int cons[MAX_MUX];
 } MuxDriver;
 
 
@@ -360,11 +363,11 @@
     int m = chr->focus;
     MuxDriver *d = chr->opaque;
 
-    while (d->prod != d->cons &&
+    while (d->prod[m] != d->cons[m] &&
            d->chr_can_read[m] &&
            d->chr_can_read[m](d->ext_opaque[m])) {
         d->chr_read[m](d->ext_opaque[m],
-                       &d->buffer[d->cons++ & MUX_BUFFER_MASK], 1);
+                       &d->buffer[m][d->cons[m]++ & MUX_BUFFER_MASK], 1);
     }
 }
 
@@ -372,11 +375,12 @@
 {
     CharDriverState *chr = opaque;
     MuxDriver *d = chr->opaque;
+    int m = chr->focus;
 
-    if ((d->prod - d->cons) < MUX_BUFFER_SIZE)
+    if ((d->prod[m] - d->cons[m]) < MUX_BUFFER_SIZE)
         return 1;
-    if (d->chr_can_read[chr->focus])
-        return d->chr_can_read[chr->focus](d->ext_opaque[chr->focus]);
+    if (d->chr_can_read[m])
+        return d->chr_can_read[m](d->ext_opaque[m]);
     return 0;
 }
 
@@ -391,12 +395,12 @@
 
     for(i = 0; i < size; i++)
         if (mux_proc_byte(chr, d, buf[i])) {
-            if (d->prod == d->cons &&
+            if (d->prod[m] == d->cons[m] &&
                 d->chr_can_read[m] &&
                 d->chr_can_read[m](d->ext_opaque[m]))
                 d->chr_read[m](d->ext_opaque[m], &buf[i], 1);
             else
-                d->buffer[d->prod++ & MUX_BUFFER_MASK] = buf[i];
+                d->buffer[m][d->prod[m]++ & MUX_BUFFER_MASK] = buf[i];
         }
 }