Re: [PATCH v2 2/2] Added parameter to take screenshot with screendump as

[Markus Armbruster]

Kshitij Suri <kshitij.suri@nutanix.com> writes:

> From: "kshitij.suri" <kshitij.suri@nutanix.com>
>
> Currently screendump only supports PPM format, which is un-compressed and not
> standard. Added a "format" parameter to qemu monitor screendump capabilites
> to support PNG image capture using libpng. The param was added in QAPI schema
> of screendump present in ui.json along with png_save() function which converts
> pixman_image to PNG. HMP command equivalent was also modified to support the
> feature.
>
> Example usage:
> { "execute": "screendump", "arguments": { "filename": "/tmp/image",
> "format":"png" } }
>
> Resolves: https://gitlab.com/qemu-project/qemu/-/issues/718
>
> Signed-off-by: Kshitij Suri <kshitij.suri@nutanix.com>
> ---
> diff to v1:
>   - Removed repeated alpha conversion operation.
>   - Modified logic to mirror png conversion in vnc-enc-tight.c file.
>   - Added a new CONFIG_PNG parameter for libpng support.
>   - Changed input format to enum instead of string.
>   - Improved error handling.
>  hmp-commands.hx    |  11 ++---
>  monitor/hmp-cmds.c |  19 ++++++++-
>  qapi/ui.json       |  24 +++++++++--
>  ui/console.c       | 102 +++++++++++++++++++++++++++++++++++++++++++--
>  4 files changed, 144 insertions(+), 12 deletions(-)
>
> diff --git a/hmp-commands.hx b/hmp-commands.hx
> index 70a9136ac2..5eda4eeb24 100644
> --- a/hmp-commands.hx
> +++ b/hmp-commands.hx
> @@ -244,17 +244,18 @@ ERST
>  
>      {
>          .name       = "screendump",
> -        .args_type  = "filename:F,device:s?,head:i?",
> -        .params     = "filename [device [head]]",
> -        .help       = "save screen from head 'head' of display device 
> 'device' "
> -                      "into PPM image 'filename'",
> +        .args_type  = "filename:F,device:s?,head:i?,format:f?",
> +        .params     = "filename [device [head]] [format]",
> +        .help       = "save screen from head 'head' of display device 
> 'device'"
> +                      "in specified format 'format' as image 'filename'."
> +                      "Currently only 'png' and 'ppm' formats are 
> supported.",
>          .cmd        = hmp_screendump,
>          .coroutine  = true,
>      },
>  
>  SRST
>  ``screendump`` *filename*
> -  Save screen into PPM image *filename*.
> +  Save screen as an image *filename*, with default format of PPM.
>  ERST
>  
>      {
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index 8c384dc1b2..9a640146eb 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -1677,9 +1677,26 @@ hmp_screendump(Monitor *mon, const QDict *qdict)
>      const char *filename = qdict_get_str(qdict, "filename");
>      const char *id = qdict_get_try_str(qdict, "device");
>      int64_t head = qdict_get_try_int(qdict, "head", 0);
> +    const char *input_format  = qdict_get_str(qdict, "format");
>      Error *err = NULL;
> +    ImageFormat format;
>  
> -    qmp_screendump(filename, id != NULL, id, id != NULL, head, &err);

The second id != NULL looks wrong.  Shouldn't it be head != NULL?
Not your patch's fault, of course.

> +    int val = qapi_enum_parse(&ImageFormat_lookup, input_format, -1, &err);
> +    if (val < 0) {
> +        goto end;
> +    }
> +
> +    switch (val) {
> +    case IMAGE_FORMAT_PNG:
> +        format = IMAGE_FORMAT_PNG;
> +        break;
> +    default:
> +        format = IMAGE_FORMAT_PPM;
> +    }
> +
> +    qmp_screendump(filename, id != NULL, id, id != NULL, head,
> +                   input_format != NULL, format, &err);
> +end:
>      hmp_handle_error(mon, err);
>  }

This isn't quite right.

qapi_enum_parse() is awkward to use.

If its second argument @input_format is null, it returns its third
argument -1.

Else, it @input_format is a valid enum string, it returns the
enumeration value, i.e. either IMAGE_FORMAT_PPM or IMAGE_FORMAT_PNG.

Else, it sets an error and returns its third argument -1.

If @input_format is null, I suspect your code jumps to
hmp_handle_error() with a null @err.  Silently does nothing.

It should default to IMAGE_FORMAT_PPM instead.

I think you want something like this (completely untested):

    val = qapi_enum_parse(&ImageFormat_lookup, input_format,
                          IMAGE_FORMAT_PPM, &err);
    if (err) {
        goto end;
    }

    qmp_screendump(filename, id != NULL, id, head != NULL, head,
                   input_format != NULL, val, &err);

>  
> diff --git a/qapi/ui.json b/qapi/ui.json
> index 9354f4c467..a6d994ba2c 100644
> --- a/qapi/ui.json
> +++ b/qapi/ui.json
> @@ -73,12 +73,27 @@
>  ##
>  { 'command': 'expire_password', 'data': {'protocol': 'str', 'time': 'str'} }
>  
> +##
> +# @ImageFormat:
> +#
> +# Supported image format types.
> +#
> +# @png: PNG format
> +#
> +# @ppm: PPM format
> +#
> +# Since: 7.0
> +#
> +##
> +{ 'enum': 'ImageFormat',
> +  'data': ['ppm', 'png'] }
> +
>  ##
>  # @screendump:
>  #
> -# Write a PPM of the VGA screen to a file.
> +# Write a screenshot of the VGA screen to a file.

Let's improve this to

   # Capture the contents of a screen and write it to a file.

>  #
> -# @filename: the path of a new PPM file to store the image
> +# @filename: the path of a new file to store the image
>  #
>  # @device: ID of the display device that should be dumped. If this parameter
>  #          is missing, the primary display will be used. (Since 2.12)
> @@ -87,6 +102,8 @@
>  #        parameter is missing, head #0 will be used. Also note that the head
>  #        can only be specified in conjunction with the device ID. (Since 
> 2.12)
>  #
> +# @format: image format for screendump is specified. (default: ppm) (Since 
> 7.0)
> +#
>  # Returns: Nothing on success
>  #
>  # Since: 0.14
> @@ -99,7 +116,8 @@
>  #
>  ##
>  { 'command': 'screendump',
> -  'data': {'filename': 'str', '*device': 'str', '*head': 'int'},
> +  'data': {'filename': 'str', '*device': 'str', '*head': 'int',
> +           '*format': 'ImageFormat'},
>    'coroutine': true }
>  
>  ##

[...]

> @@ -327,7 +413,8 @@ static void graphic_hw_update_bh(void *con)
>  /* Safety: coroutine-only, concurrent-coroutine safe, main thread only */
>  void coroutine_fn
>  qmp_screendump(const char *filename, bool has_device, const char *device,
> -               bool has_head, int64_t head, Error **errp)
> +               bool has_head, int64_t head, bool has_format,
> +               ImageFormat format, Error **errp)

Please break the line like

                  bool has_head, int64_t head,
                  bool has_format, ImageFormat format, Error **errp)

>  {
>      g_autoptr(pixman_image_t) image = NULL;
>      QemuConsole *con;
> @@ -383,8 +470,17 @@ qmp_screendump(const char *filename, bool has_device, 
> const char *device,
>       * yields and releases the BQL. It could produce corrupted dump, but
>       * it should be otherwise safe.
>       */
> -    if (!ppm_save(fd, image, errp)) {
> -        qemu_unlink(filename);
> +
> +    if (has_format && format == IMAGE_FORMAT_PNG) {
> +        /* PNG format specified for screendump */
> +        if (!png_save(fd, image, errp)) {
> +            qemu_unlink(filename);
> +        }
> +    } else {
> +        /* PPM format specified/default for screendump */
> +        if (!ppm_save(fd, image, errp)) {
> +            qemu_unlink(filename);
> +        }
>      }
>  }