Re: [Qemu-devel] [PATCH v3 35/38] console: make screendump asynchronous

[Marc-André Lureau]

Hi

On Thu, Apr 12, 2018 at 4:48 PM, Dr. David Alan Gilbert
<address@hidden> wrote:
> * Marc-André Lureau (address@hidden) wrote:
>> Make screendump asynchronous to provide correct screendumps.
>>
>> HMP doesn't have async support, so it has to remain synchronous and
>> potentially incorrect to avoid potential races.
>>
>> Fixes:
>> https://bugzilla.redhat.com/show_bug.cgi?id=1230527
>>
>> Signed-off-by: Marc-André Lureau <address@hidden>
>
> Hi,
>   Looking at this and the previous pair of patches, I think we'd be
> better if we defined that async commands took a callback function
> pointer and data that they call.
>
>   Here we've got 'graphic_hw_update_done' that explicitly walks qmp
> lists; but I think it's better just to pass graphic_hw_update() the
> completion data together with a callback function and it calls that when
> it's done.
>
> (Also isn't it a little bit of a race, calling graphic_hw_update() and
> *then* adding the entry to the list? Can't it end up calling the _done()
> before we've added it to the list).
>
> Also, do we need a list of outstanding screendumps, or should we just
> have a list of async commands.
>
> It wouldn't seem hard to use the async-QMP command from the HMP
> and then just provide a way to tell whether it had finished.
>

I should have updated the commit message, but the following patches do
introduce async-QMP support for HMP (by suspending HMP monitor, just
like QMP).

> Dave
>
>> ---
>>  qapi/ui.json         |  3 +-
>>  include/ui/console.h |  3 ++
>>  hmp.c                |  2 +-
>>  ui/console.c         | 99 ++++++++++++++++++++++++++++++++++++++++----
>>  4 files changed, 96 insertions(+), 11 deletions(-)
>>
>> diff --git a/qapi/ui.json b/qapi/ui.json
>> index 5d01ad4304..4d2c326fb9 100644
>> --- a/qapi/ui.json
>> +++ b/qapi/ui.json
>> @@ -96,7 +96,8 @@
>>  #
>>  ##
>>  { 'command': 'screendump',
>> -  'data': {'filename': 'str', '*device': 'str', '*head': 'int'} }
>> +  'data': {'filename': 'str', '*device': 'str', '*head': 'int'},
>> +  'async': true }
>>
>>  ##
>>  # == Spice
>> diff --git a/include/ui/console.h b/include/ui/console.h
>> index fc21621656..0c02190963 100644
>> --- a/include/ui/console.h
>> +++ b/include/ui/console.h
>> @@ -74,6 +74,9 @@ struct MouseTransformInfo {
>>  };
>>
>>  void hmp_mouse_set(Monitor *mon, const QDict *qdict);
>> +void hmp_screendump_sync(const char *filename,
>> +                         bool has_device, const char *device,
>> +                         bool has_head, int64_t head, Error **errp);
>>
>>  /* keysym is a unicode code except for special keys (see QEMU_KEY_xxx
>>     constants) */
>> diff --git a/hmp.c b/hmp.c
>> index 679467d85a..da9008fe63 100644
>> --- a/hmp.c
>> +++ b/hmp.c
>> @@ -2144,7 +2144,7 @@ void hmp_screendump(Monitor *mon, const QDict *qdict)
>>      int64_t head = qdict_get_try_int(qdict, "head", 0);
>>      Error *err = NULL;
>>
>> -    qmp_screendump(filename, id != NULL, id, id != NULL, head, &err);
>> +    hmp_screendump_sync(filename, id != NULL, id, id != NULL, head, &err);
>>      hmp_handle_error(mon, &err);
>>  }
>>
>> diff --git a/ui/console.c b/ui/console.c
>> index 29234605a7..da51861191 100644
>> --- a/ui/console.c
>> +++ b/ui/console.c
>> @@ -32,6 +32,7 @@
>>  #include "chardev/char-fe.h"
>>  #include "trace.h"
>>  #include "exec/memory.h"
>> +#include "monitor/monitor.h"
>>
>>  #define DEFAULT_BACKSCROLL 512
>>  #define CONSOLE_CURSOR_PERIOD 500
>> @@ -116,6 +117,12 @@ typedef enum {
>>      TEXT_CONSOLE_FIXED_SIZE
>>  } console_type_t;
>>
>> +struct qmp_screendump {
>> +    gchar *filename;
>> +    QmpReturn *ret;
>> +    QLIST_ENTRY(qmp_screendump) link;
>> +};
>> +
>>  struct QemuConsole {
>>      Object parent;
>>
>> @@ -165,6 +172,8 @@ struct QemuConsole {
>>      QEMUFIFO out_fifo;
>>      uint8_t out_fifo_buf[16];
>>      QEMUTimer *kbd_timer;
>> +
>> +    QLIST_HEAD(, qmp_screendump) qmp_screendumps;
>>  };
>>
>>  struct DisplayState {
>> @@ -190,6 +199,8 @@ static void dpy_refresh(DisplayState *s);
>>  static DisplayState *get_alloc_displaystate(void);
>>  static void text_console_update_cursor_timer(void);
>>  static void text_console_update_cursor(void *opaque);
>> +static void ppm_save(const char *filename, DisplaySurface *ds,
>> +                     Error **errp);
>>
>>  static void gui_update(void *opaque)
>>  {
>> @@ -256,8 +267,42 @@ static void gui_setup_refresh(DisplayState *ds)
>>      ds->have_text = have_text;
>>  }
>>
>> +static void qmp_screendump_finish(QemuConsole *con, const char *filename,
>> +                                  QmpReturn *ret)
>> +{
>> +    Error *err = NULL;
>> +    DisplaySurface *surface;
>> +    Monitor *prev_mon = cur_mon;
>> +
>> +    if (qmp_return_is_cancelled(ret)) {
>> +        return;
>> +    }
>> +
>> +    cur_mon = qmp_return_get_monitor(ret);
>> +    surface = qemu_console_surface(con);
>> +
>> +    /* FIXME: async save with coroutine? it would have to copy or lock
>> +     * the surface. */
>> +    ppm_save(filename, surface, &err);
>> +
>> +    if (err) {
>> +        qmp_return_error(ret, err);
>> +    } else {
>> +        qmp_screendump_return(ret);
>> +    }
>> +    cur_mon = prev_mon;
>> +}
>> +
>>  void graphic_hw_update_done(QemuConsole *con)
>>  {
>> +    struct qmp_screendump *dump, *next;
>> +
>> +    QLIST_FOREACH_SAFE(dump, &con->qmp_screendumps, link, next) {
>> +        qmp_screendump_finish(con, dump->filename, dump->ret);
>> +        g_free(dump->filename);
>> +        QLIST_REMOVE(dump, link);
>> +        g_free(dump);
>> +    }
>>  }
>>
>>  bool graphic_hw_update(QemuConsole *con)
>> @@ -358,35 +403,70 @@ write_err:
>>      goto out;
>>  }
>>
>> -void qmp_screendump(const char *filename, bool has_device, const char 
>> *device,
>> -                    bool has_head, int64_t head, Error **errp)
>> +
>> +static QemuConsole *get_console(bool has_device, const char *device,
>> +                                bool has_head, int64_t head, Error **errp)
>>  {
>> -    QemuConsole *con;
>> -    DisplaySurface *surface;
>> +    QemuConsole *con = NULL;
>>
>>      if (has_device) {
>>          con = qemu_console_lookup_by_device_name(device, has_head ? head : 
>> 0,
>>                                                   errp);
>> -        if (!con) {
>> -            return;
>> -        }
>>      } else {
>>          if (has_head) {
>>              error_setg(errp, "'head' must be specified together with 
>> 'device'");
>> -            return;
>> +            return NULL;
>>          }
>>          con = qemu_console_lookup_by_index(0);
>>          if (!con) {
>>              error_setg(errp, "There is no console to take a screendump 
>> from");
>> -            return;
>>          }
>>      }
>>
>> +    return con;
>> +}
>> +
>> +void hmp_screendump_sync(const char *filename,
>> +                         bool has_device, const char *device,
>> +                         bool has_head, int64_t head, Error **errp)
>> +{
>> +    DisplaySurface *surface;
>> +    QemuConsole *con = get_console(has_device, device, has_head, head, 
>> errp);
>> +
>> +    if (!con) {
>> +        return;
>> +    }
>> +    /* This may not complete the drawing with Spice, you may have
>> +     * glitches or outdated dumps, use qmp instead! */
>>      graphic_hw_update(con);
>>      surface = qemu_console_surface(con);
>>      ppm_save(filename, surface, errp);
>>  }
>>
>> +void qmp_screendump(const char *filename,
>> +                    bool has_device, const char *device,
>> +                    bool has_head, int64_t head,
>> +                    QmpReturn *qret)
>> +{
>> +    Error *err = NULL;
>> +    bool async;
>> +    QemuConsole *con = get_console(has_device, device, has_head, head, 
>> &err);
>> +
>> +    if (!con) {
>> +        qmp_return_error(qret, err);
>> +        return;
>> +    }
>> +    async = graphic_hw_update(con);
>> +    if (async) {
>> +        struct qmp_screendump *dump = g_new(struct qmp_screendump, 1);
>> +        dump->filename = g_strdup(filename);
>> +        dump->ret = qret;
>> +        QLIST_INSERT_HEAD(&con->qmp_screendumps, dump, link);
>> +    } else {
>> +        qmp_screendump_finish(con, filename, qret);
>> +    }
>> +}
>> +
>>  void graphic_hw_text_update(QemuConsole *con, console_ch_t *chardata)
>>  {
>>      if (!con) {
>> @@ -1280,6 +1360,7 @@ static QemuConsole *new_console(DisplayState *ds, 
>> console_type_t console_type,
>>      obj = object_new(TYPE_QEMU_CONSOLE);
>>      s = QEMU_CONSOLE(obj);
>>      s->head = head;
>> +    QLIST_INIT(&s->qmp_screendumps);
>>      object_property_add_link(obj, "device", TYPE_DEVICE,
>>                               (Object **)&s->device,
>>                               object_property_allow_set_link,
>> --
>> 2.17.0.rc1.1.g4c4f2b46a3
>>
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
>



-- 
Marc-André Lureau