Re: [Qemu-devel] [PATCH v4 4/8] device_tree: qemu_fdt_getprop converted to use the error API

[Peter Crosthwaite <crosthwaitepeter@gmail.com>]

On Fri, Jan 08, 2016 at 09:32:01AM +0000, Eric Auger wrote:
> Current qemu_fdt_getprop exits if the property is not found. It is
> sometimes needed to read an optional property, in which case we do
> not wish to exit but simply returns a null value.
> 
> This patch converts qemu_fdt_getprop to accept an Error **, and existing
> users are converted to pass &error_fatal. This preserves the existing
> behaviour. Then to use the API with your optional semantic a null
> parameter can be conveyed.
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>

Reviewed-by: Peter Crosthwaite <crosthwaite.peter@gmail.com>

> 
> ---
> 
> v1 -> v2:
> - add a doc comment in the header file
> 
> RFC -> v1:
> - get rid of qemu_fdt_getprop_optional and implement Peter's suggestion
>   that consists in using the error API
> 
> Signed-off-by: Eric Auger <eric.auger@linaro.org>
> ---
>  device_tree.c                | 11 ++++++-----
>  include/sysemu/device_tree.h | 15 ++++++++++++++-
>  2 files changed, 20 insertions(+), 6 deletions(-)
> 
> diff --git a/device_tree.c b/device_tree.c
> index 8441e01..6ecc9da 100644
> --- a/device_tree.c
> +++ b/device_tree.c
> @@ -321,18 +321,18 @@ int qemu_fdt_setprop_string(void *fdt, const char *node_path,
>  }
>  
>  const void *qemu_fdt_getprop(void *fdt, const char *node_path,
> -                             const char *property, int *lenp)
> +                             const char *property, int *lenp, Error **errp)
>  {
>      int len;
>      const void *r;
> +
>      if (!lenp) {
>          lenp = &len;
>      }
>      r = fdt_getprop(fdt, findnode_nofail(fdt, node_path), property, lenp);
>      if (!r) {
> -        error_report("%s: Couldn't get %s/%s: %s", __func__,
> -                     node_path, property, fdt_strerror(*lenp));
> -        exit(1);
> +        error_setg(errp, "%s: Couldn't get %s/%s: %s", __func__,
> +                  node_path, property, fdt_strerror(*lenp));
>      }
>      return r;
>  }
> @@ -341,7 +341,8 @@ uint32_t qemu_fdt_getprop_cell(void *fdt, const char *node_path,
>                                 const char *property)
>  {
>      int len;
> -    const uint32_t *p = qemu_fdt_getprop(fdt, node_path, property, &len);
> +    const uint32_t *p = qemu_fdt_getprop(fdt, node_path, property, &len,
> +                                         &error_fatal);
>      if (len != 4) {
>          error_report("%s: %s/%s not 4 bytes long (not a cell?)",
>                       __func__, node_path, property);
> diff --git a/include/sysemu/device_tree.h b/include/sysemu/device_tree.h
> index 269cb1c..4d7cbb9 100644
> --- a/include/sysemu/device_tree.h
> +++ b/include/sysemu/device_tree.h
> @@ -45,8 +45,21 @@ int qemu_fdt_setprop_string(void *fdt, const char *node_path,
>  int qemu_fdt_setprop_phandle(void *fdt, const char *node_path,
>                               const char *property,
>                               const char *target_node_path);
> +/**
> + * qemu_fdt_getprop: retrieve the value of a given property
> + * @fdt: pointer to the device tree blob
> + * @node_path: node path
> + * @property: name of the property to find
> + * @lenp: fdt error if any or length of the property on success
> + * @errp: handle to an error object
> + *
> + * returns a pointer to the property on success and NULL on failure
> + * in case errp is set to &error_fatal, the function auto-asserts
> + * on error (legacy behavior)
> + */
>  const void *qemu_fdt_getprop(void *fdt, const char *node_path,
> -                             const char *property, int *lenp);
> +                             const char *property, int *lenp,
> +                             Error **errp);
>  uint32_t qemu_fdt_getprop_cell(void *fdt, const char *node_path,
>                                 const char *property);
>  uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
> -- 
> 1.9.1
>