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>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/branches/stable_0_10_0@6693 c046a42c-6fe2-441c-8c8c-71466251a162

qemu-char.c

@@ -225,12 +225,15 @@ typedef struct {
     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 @@ static void mux_chr_accept_input(CharDriverState *chr)
     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 @@ static int mux_chr_can_read(void *opaque)
 {
     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 @@ static void mux_chr_read(void *opaque, const uint8_t *buf, int size)
 
     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];
         }
 }