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

[Eric Blake <eblake@redhat.com>]

On Fri, Feb 25, 2022 at 11:58:30AM +0000, Kshitij Suri wrote:
> 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>
> ---

> +        .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*.

Maybe:

as an image *filename*, with default format of PPM.

>  ERST
>  
>      {
> diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c
> index 8c384dc1b2..c300545f34 100644
> --- a/monitor/hmp-cmds.c
> +++ b/monitor/hmp-cmds.c
> @@ -1677,9 +1677,15 @@ 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 = IMAGE_FORMAT_PPM;
> +    if (input_format != NULL && strcmp(input_format, "png") == 0) {
> +        format = IMAGE_FORMAT_PNG;
> +    }

Instead of open-coding the string-to-enum translation (which will be
hard to located if we expand to a third format down the road), you
should use qapi_enum_parse(&ImageFormat_lookup, ...).

> +++ b/ui/console.c
> @@ -37,6 +37,9 @@
>  #include "exec/memory.h"
>  #include "io/channel-file.h"
>  #include "qom/object.h"
> +#ifdef CONFIG_PNG
> +#include <png.h>
> +#endif
>  
>  #define DEFAULT_BACKSCROLL 512
>  #define CONSOLE_CURSOR_PERIOD 500
> @@ -289,6 +292,87 @@ void graphic_hw_invalidate(QemuConsole *con)
>      }
>  }
>  
> +#ifdef CONFIG_PNG
> +/**
> + * png_save: Take a screenshot as PNG
> + *
> + * Saves screendump as a PNG file
> + *
> + * Returns true for success or false for error.
> + *
> + * @fd: File descriptor for PNG file.
> + * @image: Image data in pixman format.
> + * @errp: Pointer to an error.
> + */
> +static bool png_save(int fd, pixman_image_t *image, Error **errp)
> +{
> +    int width = pixman_image_get_width(image);
> +    int height = pixman_image_get_height(image);
> +    g_autofree png_struct *png_ptr = NULL;
> +    g_autofree png_info *info_ptr = NULL;
> +    g_autoptr(pixman_image_t) linebuf =
> +                            qemu_pixman_linebuf_create(PIXMAN_a8r8g8b8, width);
> +    uint8_t *buf = (uint8_t *)pixman_image_get_data(linebuf);
> +    FILE *f = fdopen(fd, "wb");
> +    int y;
> +    if (!f) {
> +        error_setg(errp, "Failed to create file from file descriptor");

error_setg_errno() might be nicer to use here, since fdopen() failure sets errno.

> +        return false;
> +    }
> +
> +    png_ptr = png_create_write_struct(PNG_LIBPNG_VER_STRING, NULL,
> +                                           NULL, NULL);

Indentation looks off.

> +    if (!png_ptr) {
> +        error_setg(errp, "PNG creation failed. Unable to write struct");
> +        free(f);

free() is the wrong function to call on FILE*.  You meant fclose().

> +        return false;
> +    }
> +
> +    info_ptr = png_create_info_struct(png_ptr);
> +
> +    if (!info_ptr) {
> +        error_setg(errp, "PNG creation failed. Unable to write info");
> +        free(f);

and again

> +        png_destroy_write_struct(&png_ptr, &info_ptr);
> +        return false;
> +    }
> +
> +    png_init_io(png_ptr, f);
> +
> +    png_set_IHDR(png_ptr, info_ptr, width, height, 8,
> +                 PNG_COLOR_TYPE_RGB_ALPHA, PNG_INTERLACE_NONE,
> +                 PNG_COMPRESSION_TYPE_BASE, PNG_FILTER_TYPE_BASE);
> +
> +    png_write_info(png_ptr, info_ptr);
> +
> +    for (y = 0; y < height; ++y) {
> +        qemu_pixman_linebuf_fill(linebuf, image, width, 0, y);
> +        png_write_row(png_ptr, buf);
> +    }
> +    qemu_pixman_image_unref(linebuf);
> +
> +    png_write_end(png_ptr, NULL);
> +
> +    png_destroy_write_struct(&png_ptr, &info_ptr);
> +
> +    if (fclose(f) != 0) {
> +        error_setg(errp, "PNG creation failed. Unable to close file");

Another spot for error_setg_errno

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org