Re: [PATCH v3 02/33] system/device_tree: add few parsing and traversal helpers

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Apr 02, 2026 at 11:55:47PM +0200, Ruslan Ruslichenko wrote:
> From: Ruslan Ruslichenko <Ruslan_Ruslichenko@epam.com>
> 
> The patch adds few utility functions for parsing FDT nodes.
> The helpers are required for upcoming Hardware device tree
> feature.

If you're building an entire fdt based machine type, it really seems
like you might want a "live" dt representation - the flattened format
is great for communicating between things, but it's not a good data
structure if you're actively consulting it.

> 
> Signed-off-by: Ruslan Ruslichenko <Ruslan_Ruslichenko@epam.com>
> ---
>  include/system/device_tree.h |  22 ++++
>  system/device_tree.c         | 194 +++++++++++++++++++++++++++++++++++
>  2 files changed, 216 insertions(+)
> 
> diff --git a/include/system/device_tree.h b/include/system/device_tree.h
> index 5667ff9538..bc378d38d0 100644
> --- a/include/system/device_tree.h
> +++ b/include/system/device_tree.h
> @@ -116,6 +116,11 @@ const void *qemu_fdt_getprop(void *fdt, const char *node_path,
>  uint32_t qemu_fdt_getprop_cell(void *fdt, const char *node_path,
>                                 const char *property, int cell_id,
>                                 Error **errp);
> +
> +const void *qemu_fdt_getprop_inherited(void *fdt, const char *node_path,
> +                             const char *property, int *lenp, Error **errp);
> +uint32_t qemu_fdt_getprop_cell_inherited(void *fdt, const char *node_path,
> +                               const char *property, int cell_id, Error **errp);
>  uint32_t qemu_fdt_get_phandle(void *fdt, const char *path);
>  uint32_t qemu_fdt_alloc_phandle(void *fdt);
>  int qemu_fdt_nop_node(void *fdt, const char *node_path);
> @@ -191,6 +196,23 @@ int qemu_fdt_setprop_sized_cells_from_array(void *fdt,
>                                                  qdt_tmp);                 \
>      })
>  
> +/* node queries */
> +
> +int qemu_devtree_get_num_children(void *fdt, const char *node_path);
> +int qemu_devtree_get_children(void *fdt, const char *node_path,
> +                                     int max_paths, char **returned_paths);
> +int qemu_devtree_num_props(void *fdt, const char *node_path);
> +
> +/* node getters */
> +
> +int qemu_devtree_get_node_by_phandle(void *fdt, char *node_path, int phandle);
> +char *qemu_devtree_getparent(void *fdt, const char *current);
> +
> +/* misc */
> +
> +int devtree_get_num_nodes(void *fdt);
> +
> +#define DT_PATH_LENGTH 1024
>  
>  /**
>   * qemu_fdt_randomize_seeds:
> diff --git a/system/device_tree.c b/system/device_tree.c
> index d2db7bd355..1a70223712 100644
> --- a/system/device_tree.c
> +++ b/system/device_tree.c
> @@ -464,6 +464,96 @@ uint32_t qemu_fdt_getprop_cell(void *fdt, const char *node_path,
>      return be32_to_cpu(p[cell_id]);
>  }
>  
> +const void *qemu_fdt_getprop_inherited(void *fdt, const char *node_path,
> +                             const char *property, int *lenp, Error **errp)
> +{
> +    const void *found_val = NULL;
> +    int found_len = 0;
> +    int curr_offset = 0;
> +    int temp_len;
> +    char **tokens;
> +    char **iter;
> +
> +    found_val = fdt_getprop(fdt, 0, property, &found_len);
> +
> +    tokens = g_strsplit(node_path + 1, "/", -1);
> +
> +    for (iter = tokens; *iter != NULL; iter++) {
> +        if (**iter == '\0') {
> +            continue;
> +        }
> +
> +        curr_offset = fdt_subnode_offset(fdt, curr_offset, *iter);
> +        if (curr_offset < 0) {
> +            error_setg(errp, "%s: Path '%s' not found",
> +                       __func__, *iter);
> +            g_strfreev(tokens);
> +            return NULL;
> +        }
> +
> +        const void *val = fdt_getprop(fdt, curr_offset, property, &temp_len);
> +        if (val) {
> +            found_val = val;
> +            found_len = temp_len;
> +        }
> +    }
> +    g_strfreev(tokens);
> +
> +    if (!found_val) {
> +        error_setg(errp, "%s: Property '%s' not found",
> +                   __func__, property);
> +        return NULL;
> +    }
> +
> +    if (lenp) {
> +        *lenp = found_len;
> +    }
> +
> +    return found_val;
> +}
> +
> +uint32_t qemu_fdt_getprop_cell_inherited(void *fdt, const char *node_path,
> +                               const char *property, int cell_id, Error **errp)
> +{
> +    int len;
> +    const uint32_t *p;
> +
> +    p = qemu_fdt_getprop_inherited(fdt, node_path, property, &len, errp);
> +    if (!p) {
> +        return 0;
> +    }
> +    if (len < (cell_id + 1) * 4) {
> +        error_setg(errp,
> +                   "%s: %s/%s is too short, need %d bytes for cell ind %d",
> +                   __func__, node_path, property, (cell_id + 1) * 4, cell_id);
> +        return 0;
> +    }
> +    return be32_to_cpu(p[cell_id]);
> +}
> +
> +char *qemu_devtree_getparent(void *fdt, const char *current)
> +{
> +    const char *sep;
> +    int len;
> +
> +    if (!current || !strcmp(current, "/")) {
> +        return NULL;
> +    }
> +
> +    sep = strrchr(current, '/');
> +    if (!sep) {
> +        return NULL;
> +    }
> +
> +    if (sep == current) {
> +        len = 1;
> +    } else {
> +        len = sep - current;
> +    }
> +
> +    return g_strndup(current, len);
> +}
> +
>  uint32_t qemu_fdt_get_phandle(void *fdt, const char *path)
>  {
>      uint32_t r;
> @@ -631,6 +721,110 @@ out:
>      return ret;
>  }
>  
> +int qemu_devtree_num_props(void *fdt, const char *node_path)
> +{
> +    int offset = fdt_path_offset(fdt, node_path);
> +    int ret = 0;
> +
> +    for (offset = fdt_first_property_offset(fdt, offset);
> +            offset != -FDT_ERR_NOTFOUND;
> +            offset = fdt_next_property_offset(fdt, offset)) {
> +        ret++;
> +    }
> +    return ret;
> +}
> +
> +int qemu_devtree_get_children(void *fdt, const char *node_path,
> +                                     int max_paths, char **returned_paths)
> +{
> +    int count = 0;
> +    int subnode;
> +    const char *name;
> +    int offset = fdt_path_offset(fdt, node_path);
> +
> +    if (offset < 0) {
> +        return offset;
> +    }
> +
> +    bool is_root = (strcmp(node_path, "/") == 0);
> +
> +    fdt_for_each_subnode(subnode, fdt, offset) {
> +        if (count >= max_paths) {
> +            break;
> +        }
> +        name = fdt_get_name(fdt, subnode, NULL);
> +        if (returned_paths) {
> +            returned_paths[count] = g_strdup_printf("%s/%s",
> +                                                is_root ? "" : node_path, name);
> +        }
> +
> +        ++count;
> +    }
> +
> +    return count;
> +}
> +
> +int qemu_devtree_get_num_children(void *fdt, const char *node_path)
> +{
> +    int count = 0;
> +    int subnode;
> +    int offset = fdt_path_offset(fdt, node_path);
> +
> +    if (offset < 0) {
> +        return offset;
> +    }
> +
> +    fdt_for_each_subnode(subnode, fdt, offset) {
> +        ++count;
> +    }
> +
> +    return count;
> +}
> +
> +int qemu_devtree_get_node_by_phandle(void *fdt, char *node_path, int phandle)
> +{
> +    int offset = 0, cur_depth = 0;
> +    int path_lens[64] = { 0 };
> +
> +    for (offset = 0; offset >= 0; offset = fdt_next_node(fdt, offset,
> +                                                         &cur_depth)) {
> +        if (cur_depth >= 64) {
> +            break;
> +        }
> +        const char *name = fdt_get_name(fdt, offset, NULL);
> +
> +        int parent_len = (cur_depth > 0) ? path_lens[cur_depth - 1] : 0;
> +        int len = snprintf(node_path + parent_len,
> +                             DT_PATH_LENGTH - parent_len,
> +                             "%s%s",
> +                             (parent_len > 1) ? "/" : "",
> +                             (cur_depth == 0) ? "/" : name);
> +
> +        path_lens[cur_depth] = parent_len + len;
> +
> +        if (fdt_get_phandle(fdt, offset) == phandle) {
> +            return 0;
> +        }
> +    }
> +
> +    return -FDT_ERR_NOTFOUND;
> +}
> +
> +int devtree_get_num_nodes(void *fdt)
> +{
> +    int num_nodes = 0;
> +    int depth = 0, offset = 0;
> +
> +    for (;;) {
> +        offset = fdt_next_node(fdt, offset, &depth);
> +        num_nodes++;
> +        if (offset <= 0 || depth <= 0) {
> +            break;
> +        }
> +    }
> +    return num_nodes;
> +}
> +
>  void qmp_dumpdtb(const char *filename, Error **errp)
>  {
>      ERRP_GUARD();
> -- 
> 2.43.0
> 

-- 
David Gibson (he or they)	| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you, not the other way
				| around.
http://www.ozlabs.org/~dgibson

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