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Re: [Libguestfs] [PATCH 4/7] hivex: Add metadata length functions for nodes and values



On Thu, Sep 01, 2011 at 06:17:36PM -0700, Alex Nelson wrote:
> This patch adds hivex_node_struct_length and hivex_value_struct_length
> to the hivex ABI, to report the amount of hive space used for each
> stored structure.
> 
> Signed-off-by: Alex Nelson <ajnelson cs ucsc edu>
> ---
>  generator/generator.ml |   12 ++++++++++++
>  lib/hivex.c            |   33 +++++++++++++++++++++++++++++++++
>  2 files changed, 45 insertions(+), 0 deletions(-)
> 
> diff --git a/generator/generator.ml b/generator/generator.ml
> index 15ebc44..5a71930 100755
> --- a/generator/generator.ml
> +++ b/generator/generator.ml
> @@ -264,6 +264,18 @@ information, and the value itself.  Also, C<hivex_value_*> functions
>  below which can be used to return the value in a more useful form when
>  you know the type in advance.";
>  
> +  "node_struct_length", (RSize, [AHive; ANode "node"]),
> +    "return the length of a node",
> +    "\
> +Return the length of the node data structure.  Returns 0
> +and sets errno on error.";
> +
> +  "value_struct_length", (RSize, [AHive; AValue "val"]),
> +    "return the length of a value data structure",
> +    "\
> +Return the length of the value data structure.  Returns 0
> +and sets errno on error.";
> +
>    "value_value", (RLenTypeVal, [AHive; AValue "val"]),
>      "return data length, data type and data of a value",
>      "\
> diff --git a/lib/hivex.c b/lib/hivex.c
> index 61177d3..d8ffa63 100644
> --- a/lib/hivex.c
> +++ b/lib/hivex.c
> @@ -585,6 +585,30 @@ hivex_root (hive_h *h)
>    return ret;
>  }
>  
> +size_t
> +hivex_node_struct_length (hive_h *h, hive_node_h node)
> +{
> +  if (!IS_VALID_BLOCK (h, node) || !BLOCK_ID_EQ (h, node, "nk")) {
> +    errno = EINVAL;
> +    return 0;
> +  }
> +
> +  struct ntreg_nk_record *nk = (struct ntreg_nk_record *) (h->addr + node);
> +  size_t name_len = le16toh (nk->name_len);
> +  /* -1 to avoid double-counting the first name character */
> +  size_t ret = name_len + sizeof (struct ntreg_nk_record) - 1;
> +  int used;
> +  size_t seg_len = block_len (h, node, &used);
> +  if (ret > seg_len) {
> +    if (h->msglvl >= 2)
> +      fprintf (stderr, "hivex_node_struct_length: returning EFAULT because"
> +               " node name is too long (%zu, %zu)\n", name_len, seg_len);
> +    errno = EFAULT;
> +    return 0;
> +  }
> +  return ret;
> +}
> +
>  char *
>  hivex_node_name (hive_h *h, hive_node_h node)
>  {
> @@ -1190,6 +1214,15 @@ hivex_node_get_value (hive_h *h, hive_node_h node, const char *key)
>  }
>  
>  size_t
> +hivex_value_struct_length (hive_h *h, hive_value_h value) {
> +  size_t key_len = hivex_value_key_len (h, value);
> +  if (errno)
> +    return 0;
> +  /* -1 to avoid double-counting the first name character */
> +  return key_len + sizeof (struct ntreg_vk_record) - 1;
> +}

This isn't quite right.  Apart from the formatting (use GNU
conventions) you can't test errno unless you set it to zero before
calling the function, since on non-error return errno is not altered.

I will fix this before I commit it, so ACK.

Rich.

-- 
Richard Jones, Virtualization Group, Red Hat http://people.redhat.com/~rjones
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