Re: [Xen-devel] [PATCH V5 27/32] libxl: libxl-json format and load/store configuration functions

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Tue, 2014-05-13 at 22:54 +0100, Wei Liu wrote:
> Introduce a new format in libxl userdata store called "libxl-json". This
> format contains the deserialized version of domain configuration of a
> domain.
> 
> Two libxl functions to load and store domain configuration are also
> introduced. They use the new "libxl-json" format.

Is the intention that application should use these to read/modify/write
the domain config on changes, as opposed to it being internal
functionality which libxl should use to keep things up to date?

> 
> Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
> ---
>  tools/libxl/libxl.c |   68 
> +++++++++++++++++++++++++++++++++++++++++++++++++++
>  tools/libxl/libxl.h |   10 ++++++++
>  2 files changed, 78 insertions(+)
> 
> diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
> index c9475d7..b578a5c 100644
> --- a/tools/libxl/libxl.c
> +++ b/tools/libxl/libxl.c
> @@ -5751,6 +5751,74 @@ void libxl_mac_copy(libxl_ctx *ctx, libxl_mac *dst, 
> libxl_mac *src)
>      for (i = 0; i < 6; i++)
>          (*dst)[i] = (*src)[i];
>  }
> +
> +int libxl_load_domain_configuration(libxl_ctx *ctx, uint32_t domid,
> +                                    libxl_domain_config *d_config)
> +{
> +    GC_INIT(ctx);
> +    uint8_t *data;
> +    int rc, len;
> +
> +    rc = libxl_userdata_retrieve(ctx, domid, "libxl-json", &data, &len);
> +    if (rc) {
> +        LIBXL__LOG_ERRNOVAL(ctx, LIBXL__LOG_ERROR, rc,

You can use LOGEV here to shorten lines and loge below etc.

> +                            "Failed to retrieve domain configuration for 
> domain %d",
> +                            domid);
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    if (len == 0) {
> +        LIBXL__LOG_ERRNO(ctx, LIBXL__LOG_ERROR,

> +                         "Configuration data stream empty for domain %d",
> +                         domid);
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    /* Make sure this string ends with \0 -- the parser expects a NULL
> +     * terminated string.

Could this be achieved by strlen(d_config_json)+1 when saving? Assuming
that string is NULL terminated.

> +     */
> +    if (data[len-1] != '\0') {
> +        data = libxl__realloc(gc, data, len + 1);
> +        data[len] = '\0';
> +    }
> +
> +    rc = libxl_domain_config_from_json(ctx, d_config, (const char *)data);
> +
> +out:
> +    free(data);

data might have been libxl__realloc'd above, so isn't it gc'd?

> +    GC_FREE;
> +    return rc;
> +}
> +
> +int libxl_store_domain_configuration(libxl_ctx *ctx, uint32_t domid,
> +                                     libxl_domain_config *d_config)
> +{
> +    GC_INIT(ctx);
> +    char *d_config_json;
> +    int rc;
> +
> +    d_config_json = libxl_domain_config_to_json(ctx, d_config);
> +
> +    rc = libxl_userdata_store(ctx, domid, "libxl-json",
> +                              (const uint8_t *)d_config_json,
> +                              strlen(d_config_json));
> +    if (rc) {
> +        LIBXL__LOG_ERRNOVAL(ctx, LIBXL__LOG_ERROR, rc,

LOGEV.

> +                            "Failed to store domain configuration for domain 
> %d",
> +                            domid);
> +        rc = ERROR_FAIL;
> +        goto out;
> +    }
> +
> +    free(d_config_json);
> +
> +out:
> +    GC_FREE;
> +    return rc;
> +}
> +
>  /*
>   * Local variables:
>   * mode: C
> diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
> index d5dfe2e..be722b6 100644
> --- a/tools/libxl/libxl.h
> +++ b/tools/libxl/libxl.h
> @@ -1140,6 +1140,8 @@ void libxl_cpuid_set(libxl_ctx *ctx, uint32_t domid,
>   *  "xl"          domain config file in xl format, Unix line endings
>   *  "libvirt-xml" domain config file in libvirt XML format.  See
>   *                http://libvirt.org/formatdomain.html
> + *  "libxl-json"  domain config file in JSON format, generated by
> + *                libxl

I think I would mention libxl_domain_config. Something like
"libxl_domain_config object in JSON format, generated by libxl."
perhaps.


Ian.


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