Re: [PATCH v4 2/2] Added parameter to take screenshot with screendump as PNG

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Markus Armbruster (armbru@redhat.com) wrote:
> Dave, please have a look at the HMP compatibility issue in
> hmp-command.hx below.
> 
> Kshitij Suri <kshitij.suri@nutanix.com> writes:
> 
> > Currently screendump only supports PPM format, which is un-compressed and not
> > standard.
> 
> If "standard" means "have to pay a standards organization $$$ to access
> the spec", PPM is not standard.  If it means "widely supported", it
> certainly is.  I'd drop "and not standard".  Suggestion, not demand.
> 
> >           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.
> 
> Suggest to use imperative mood to describe the commit, and omit details
> that aren't necessary here:
> 
>             Add a "format" parameter to QMP and HMP screendump command
>   to support PNG image capture using libpng.
> 
> >
> > Example usage:
> > { "execute": "screendump", "arguments": { "filename": "/tmp/image",
> > "format":"png" } }
> 
> Providing an example in the commit message is always nice, thanks!
> 
> >
> > Resolves: https://gitlab.com/qemu-project/qemu/-/issues/718
> >
> > Signed-off-by: Kshitij Suri <kshitij.suri@nutanix.com>
> >
> > Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
> > ---
> >  hmp-commands.hx    |  11 ++---
> >  monitor/hmp-cmds.c |  12 +++++-
> >  qapi/ui.json       |  24 +++++++++--
> >  ui/console.c       | 101 +++++++++++++++++++++++++++++++++++++++++++--
> >  4 files changed, 136 insertions(+), 12 deletions(-)
> >
> > diff --git a/hmp-commands.hx b/hmp-commands.hx
> > index 8476277aa9..19b7cab595 100644
> > --- a/hmp-commands.hx
> > +++ b/hmp-commands.hx
> > @@ -244,11 +244,12 @@ 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'",
> > -        .cmd        = hmp_screendump,
> > +        .args_type  = "filename:F,format:s?,device:s?,head:i?",
> 
> Incompatible change: meaning of "screendump ONE TWO" changes from
> filename=ONE, device=TWO to filename=ONE, format=TWO.
> 
> As HMP is not a stable interface, incompatible change is permissible.
> But is this one wise?
> 
> Could we add the new argument at the end instead?
> 
>             .args_type  = "filename:F,device:s?,head:i?,format:s?",
> 
> Could we do *without* an argument, and derive the format from the
> filename extension?  .png means format=png, anything else format=ppm.
> Would be a bad idea for QMP.  Okay for HMP?

Could we use the new optional flag with value that Stefan Reiter
added in 26fcd76 ? (and used in 675fd3c)
In which case I think we'd have:
  "filename:F,format:-fs,device:s?,head:i?"

That would seem cleanest;  Extracting from the filename would be OKish
if it errored if the format wasn't obvious.

Dave


> > +        .params     = "filename [format] [device [head]]",
> 
> This tells us that parameter format can be omitted like so
> 
>     screendump foo.ppm device-id
> 
> which isn't true.  Better: "filename [format [device [head]]".
> 
> > +        .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,
> >      },
> >  
> > diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> > index 634968498b..2442bfa989 100644
> > --- a/monitor/hmp-cmds.c
> > +++ b/monitor/hmp-cmds.c
> > @@ -1720,9 +1720,19 @@ 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_try_str(qdict, "format");
> >      Error *err = NULL;
> > +    ImageFormat format;
> >  
> > -    qmp_screendump(filename, id != NULL, id, id != NULL, head, &err);
> > +    format = qapi_enum_parse(&ImageFormat_lookup, input_format,
> > +                              IMAGE_FORMAT_PPM, &err);
> > +    if (err) {
> > +        goto end;
> > +    }
> > +
> > +    qmp_screendump(filename, id != NULL, id, id != NULL, head,
> > +                   input_format != NULL, format, &err);
> > +end:
> >      hmp_handle_error(mon, err);
> >  }
> >  
> > diff --git a/qapi/ui.json b/qapi/ui.json
> > index 664da9e462..24371fce05 100644
> > --- a/qapi/ui.json
> > +++ b/qapi/ui.json
> > @@ -157,12 +157,27 @@
> >  ##
> >  { 'command': 'expire_password', 'boxed': true, 'data': 'ExpirePasswordOptions' }
> >  
> > +##
> > +# @ImageFormat:
> > +#
> > +# Supported image format types.
> > +#
> > +# @png: PNG format
> > +#
> > +# @ppm: PPM format
> > +#
> > +# Since: 7.1
> > +#
> > +##
> > +{ 'enum': 'ImageFormat',
> > +  'data': ['ppm', 'png'] }
> > +
> >  ##
> >  # @screendump:
> >  #
> > -# Write a PPM of the VGA screen to a file.
> > +# 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)
> > @@ -171,6 +186,8 @@
> >  #        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 7.1)
> 
> Recommend
> 
>    # @format: image format for screendump (default: ppm) (Since 7.1)
> 
> > +#
> >  # Returns: Nothing on success
> >  #
> >  # Since: 0.14
> > @@ -183,7 +200,8 @@
> >  #
> >  ##
> >  { 'command': 'screendump',
> > -  'data': {'filename': 'str', '*device': 'str', '*head': 'int'},
> > +  'data': {'filename': 'str', '*device': 'str', '*head': 'int',
> > +           '*format': 'ImageFormat'},
> >    'coroutine': true }
> >  
> >  ##
> 
> QAPI schema
> Acked-by: Markus Armbruster <armbru@redhat.com>
> 
> [...]
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK