Re: [PATCH v4 08/13] libfdt: Add fdt_path_offset_namelen

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Tue, Jul 05, 2016 at 10:26:41AM +0200, Maxime Ripard wrote:
> Add a namelen variant of fdt_path_offset to retrieve the node offset using
> only a fixed number of characters.
> 
> Reviewed-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> Signed-off-by: Maxime Ripard <maxime.ripard-wi1+55ScJUtKEb57/3fJTNBPR1lH4CV8@public.gmane.org>
> ---
>  include/libfdt.h    | 16 +++++++++++++++-
>  lib/libfdt/fdt_ro.c | 18 ++++++++++--------
>  2 files changed, 25 insertions(+), 9 deletions(-)
> 
> diff --git a/include/libfdt.h b/include/libfdt.h
> index 4643be5adf39..f13b01f08f71 100644
> --- a/include/libfdt.h
> +++ b/include/libfdt.h
> @@ -365,6 +365,17 @@ int fdt_subnode_offset_namelen(const void *fdt, int parentoffset,
>   */
>  int fdt_subnode_offset(const void *fdt, int parentoffset, const char *name);
>  
> +/**
> + * fdt_path_offset_namelen - find a tree node based on substring
> + * @fdt: pointer to the device tree blob
> + * @path: full path of the node to locate
> + * @namelen: number of characters of name to consider
> + *
> + * Identical to fdt_path_offset(), but only examine the first
> + * namelen characters of path for matching the node path.
> + */
> +int fdt_path_offset_namelen(const void *fdt, const char *path, int namelen);
> +
>  /**
>   * fdt_path_offset - find a tree node by its full path
>   * @fdt: pointer to the device tree blob
> @@ -387,7 +398,10 @@ int fdt_subnode_offset(const void *fdt, int parentoffset, const char *name);
>   *	-FDT_ERR_BADSTRUCTURE,
>   *	-FDT_ERR_TRUNCATED, standard meanings.
>   */
> -int fdt_path_offset(const void *fdt, const char *path);
> +static inline int fdt_path_offset(const void *fdt, const char *path)
> +{
> +	return fdt_path_offset_namelen(fdt, path, strlen(path));
> +}
>  
>  /**
>   * fdt_get_name - retrieve the name of a given node
> diff --git a/lib/libfdt/fdt_ro.c b/lib/libfdt/fdt_ro.c
> index 6b737b211d2e..9cc98db6e2bf 100644
> --- a/lib/libfdt/fdt_ro.c
> +++ b/lib/libfdt/fdt_ro.c
> @@ -145,10 +145,10 @@ int fdt_subnode_offset(const void *fdt, int parentoffset,
>   * "foo/bar:option" and "bar:option/otheroption", both of which happen, so
>   * first searching for either ':' or '/' does not work.
>   */
> -static const char *fdt_path_next_separator(const char *path)
> +static const char *fdt_path_next_separator(const char *path, int len)
>  {
> -	const char *sep1 = strchr(path, '/');
> -	const char *sep2 = strchr(path, ':');
> +	const void *sep1 = memchr(path, '/', len);
> +	const void *sep2 = memchr(path, ':', len);
>  
>  	if (sep1 && sep2)
>  		return (sep1 < sep2) ? sep1 : sep2;
> @@ -158,9 +158,9 @@ static const char *fdt_path_next_separator(const char *path)
>  		return sep2;
>  }
>  
> -int fdt_path_offset(const void *fdt, const char *path)
> +int fdt_path_offset_namelen(const void *fdt, const char *path, int namelen)
>  {
> -	const char *end = path + strlen(path);
> +	const char *end = path + namelen;
>  	const char *p = path;
>  	int offset = 0;
>  
> @@ -168,7 +168,7 @@ int fdt_path_offset(const void *fdt, const char *path)
>  
>  	/* see if we have an alias */
>  	if (*path != '/') {
> -		const char *q = fdt_path_next_separator(path);
> +		const char *q = fdt_path_next_separator(path, namelen);
>  
>  		if (!q)
>  			q = end;
> @@ -181,14 +181,16 @@ int fdt_path_offset(const void *fdt, const char *path)
>  		p = q;
>  	}
>  
> -	while (*p) {
> +	while (*p && (p < end)) {

The *p test should now be redundant.  If you do see a \0 within the
length specified by namelen, you should return FDT_ERR_BADPATH, rather
than just truncating at the \0.

... and I just realised that path_offset_namelen() is already
upstream, so I should fix that there too.

So what the hell is this downstream fdt_path_next_separator() nonsense for?

>  		const char *q;
>  
>  		while (*p == '/')
>  			p++;
> +
>  		if (*p == '\0' || *p == ':')
>  			return offset;
> -		q = fdt_path_next_separator(p);
> +
> +		q = fdt_path_next_separator(p, end - p);
>  		if (!q)
>  			q = end;
>  

-- 
David Gibson			| 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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