[2/2] Monitor: Make output buffer dynamic

Commit f628926bb423fa8a7e0b114511400ea9df38b76a changed monitor_flush()
to retry on qemu_chr_fe_write() errors. However, the Monitor's output
buffer can keep growing while the retry is not issued and this can
cause the buffer to overflow.

To reproduce this issue, just start qemu and type on the Monitor:

(qemu) ?

This will cause the assertion to trig.

To fix this problem this commit makes the Monitor buffer dynamic,
which means that it can grow as much as needed.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 monitor.c | 42 +++++++++++++++++++++++++-----------------
 1 file changed, 25 insertions(+), 17 deletions(-)

Il 25/03/2013 20:40, Luiz Capitulino ha scritto:
> Commit f628926bb423fa8a7e0b114511400ea9df38b76a changed monitor_flush()
> to retry on qemu_chr_fe_write() errors. However, the Monitor's output
> buffer can keep growing while the retry is not issued and this can
> cause the buffer to overflow.
> 
> To reproduce this issue, just start qemu and type on the Monitor:
> 
> (qemu) ?
> 
> This will cause the assertion to trig.
> 
> To fix this problem this commit makes the Monitor buffer dynamic,
> which means that it can grow as much as needed.

What about using a GString instead?

Paolo

> Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
> ---
>  monitor.c | 42 +++++++++++++++++++++++++-----------------
>  1 file changed, 25 insertions(+), 17 deletions(-)
> 
> diff --git a/monitor.c b/monitor.c
> index 2d9e887..c93dfe7 100644
> --- a/monitor.c
> +++ b/monitor.c
> @@ -188,8 +188,7 @@ struct Monitor {
>      int reset_seen;
>      int flags;
>      int suspend_cnt;
> -    uint8_t outbuf[1024];
> -    int outbuf_index;
> +    QString *outbuf;
>      ReadLineState *rs;
>      MonitorControl *mc;
>      CPUArchState *mon_cpu;
> @@ -271,45 +270,52 @@ static gboolean monitor_unblocked(GIOChannel *chan, GIOCondition cond,
>  void monitor_flush(Monitor *mon)
>  {
>      int rc;
> +    size_t len;
> +    const char *buf;
> +
> +    buf = qstring_get_str(mon->outbuf);
> +    len = qstring_get_length(mon->outbuf);
>  
> -    if (mon && mon->outbuf_index != 0 && !mon->mux_out) {
> -        rc = qemu_chr_fe_write(mon->chr, mon->outbuf, mon->outbuf_index);
> -        if (rc == mon->outbuf_index) {
> +    if (mon && len && !mon->mux_out) {
> +        rc = qemu_chr_fe_write(mon->chr, (const uint8_t *) buf, len);
> +        if (rc == len) {
>              /* all flushed */
> -            mon->outbuf_index = 0;
> +            QDECREF(mon->outbuf);
> +            mon->outbuf = qstring_new();
>              return;
>          }
>          if (rc > 0) {
>              /* partinal write */
> -            memmove(mon->outbuf, mon->outbuf + rc, mon->outbuf_index - rc);
> -            mon->outbuf_index -= rc;
> +            QString *tmp = qstring_from_str(buf + rc);
> +            QDECREF(mon->outbuf);
> +            mon->outbuf = tmp;
>          }
>          qemu_chr_fe_add_watch(mon->chr, G_IO_OUT, monitor_unblocked, mon);
>      }
>  }
>  
> -/* flush at every end of line or if the buffer is full */
> +/* flush at every end of line */
>  static void monitor_puts(Monitor *mon, const char *str)
>  {
>      char c;
>  
>      for(;;) {
> -        assert(mon->outbuf_index < sizeof(mon->outbuf) - 1);
>          c = *str++;
>          if (c == '\0')
>              break;
> -        if (c == '\n')
> -            mon->outbuf[mon->outbuf_index++] = '\r';
> -        mon->outbuf[mon->outbuf_index++] = c;
> -        if (mon->outbuf_index >= (sizeof(mon->outbuf) - 1)
> -            || c == '\n')
> +        if (c == '\n') {
> +            qstring_append_chr(mon->outbuf, '\r');
> +        }
> +        qstring_append_chr(mon->outbuf, c);
> +        if (c == '\n') {
>              monitor_flush(mon);
> +        }
>      }
>  }
>  
>  void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
>  {
> -    char buf[4096];
> +    char *buf;
>  
>      if (!mon)
>          return;
> @@ -318,8 +324,9 @@ void monitor_vprintf(Monitor *mon, const char *fmt, va_list ap)
>          return;
>      }
>  
> -    vsnprintf(buf, sizeof(buf), fmt, ap);
> +    buf = g_strdup_vprintf(fmt, ap);
>      monitor_puts(mon, buf);
> +    g_free(buf);
>  }
>  
>  void monitor_printf(Monitor *mon, const char *fmt, ...)
> @@ -4732,6 +4739,7 @@ void monitor_init(CharDriverState *chr, int flags)
>      }
>  
>      mon = g_malloc0(sizeof(*mon));
> +    mon->outbuf = qstring_new();
>  
>      mon->chr = chr;
>      mon->flags = flags;
>

On Mon, 25 Mar 2013 22:07:36 +0100
Paolo Bonzini <pbonzini@redhat.com> wrote:

> Il 25/03/2013 20:40, Luiz Capitulino ha scritto:
> > Commit f628926bb423fa8a7e0b114511400ea9df38b76a changed monitor_flush()
> > to retry on qemu_chr_fe_write() errors. However, the Monitor's output
> > buffer can keep growing while the retry is not issued and this can
> > cause the buffer to overflow.
> > 
> > To reproduce this issue, just start qemu and type on the Monitor:
> > 
> > (qemu) ?
> > 
> > This will cause the assertion to trig.
> > 
> > To fix this problem this commit makes the Monitor buffer dynamic,
> > which means that it can grow as much as needed.
> 
> What about using a GString instead?

Makes no difference for me (although I don't enjoy mixing QString and GString
in the same module), but if we do this with the goal of stopping QString
proliferation then we should note somewhere that it shouldn't be used in
new code anymore.