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libfdt: Add fdt_find_regions()

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Add a function to find regions in device tree given a list of nodes to
include and properties to exclude.

See the header file for full documentation.

Signed-off-by: Simon Glass <sjg@chromium.org>
This commit is contained in:
Simon Glass 2013-06-13 15:10:08 -07:00 • committed by Tom Rini
parent 399c744b22
commit 3e06cd1f97
2 changed files with 193 additions and 0 deletions
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64
include/libfdt.h
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@ -1511,4 +1511,68 @@ int fdt_del_node(void *fdt, int nodeoffset);
const char *fdt_strerror(int errval);
struct fdt_region {
int offset;
int size;
};
/**
* fdt_find_regions() - find regions in device tree
*
* Given a list of nodes to include and properties to exclude, find
* the regions of the device tree which describe those included parts.
*
* The intent is to get a list of regions which will be invariant provided
* those parts are invariant. For example, if you request a list of regions
* for all nodes but exclude the property "data", then you will get the
* same region contents regardless of any change to "data" properties.
*
* This function can be used to produce a byte-stream to send to a hashing
* function to verify that critical parts of the FDT have not changed.
*
* Nodes which are given in 'inc' are included in the region list, as
* are the names of the immediate subnodes nodes (but not the properties
* or subnodes of those subnodes).
*
* For eaxample "/" means to include the root node, all root properties
* and the FDT_BEGIN_NODE and FDT_END_NODE of all subnodes of /. The latter
* ensures that we capture the names of the subnodes. In a hashing situation
* it prevents the root node from changing at all Any change to non-excluded
* properties, names of subnodes or number of subnodes would be detected.
*
* When used with FITs this provides the ability to hash and sign parts of
* the FIT based on different configurations in the FIT. Then it is
* impossible to change anything about that configuration (include images
* attached to the configuration), but it may be possible to add new
* configurations, new images or new signatures within the existing
* framework.
*
* Adding new properties to a device tree may result in the string table
* being extended (if the new property names are different from those
* already added). This function can optionally include a region for
* the string table so that this can be part of the hash too.
*
* The device tree header is not included in the list.
*
* @fdt: Device tree to check
* @inc: List of node paths to included
* @inc_count: Number of node paths in list
* @exc_prop: List of properties names to exclude
* @exc_prop_count: Number of properties in exclude list
* @region: Returns list of regions
* @max_region: Maximum length of region list
* @path: Pointer to a temporary string for the function to use for
* building path names
* @path_len: Length of path, must be large enough to hold the longest
* path in the tree
* @add_string_tab: 1 to add a region for the string table
* @return number of regions in list. If this is >max_regions then the
* region array was exhausted. You should increase max_regions and try
* the call again.
*/
int fdt_find_regions(const void *fdt, char * const inc[], int inc_count,
char * const exc_prop[], int exc_prop_count,
struct fdt_region region[], int max_regions,
char *path, int path_len, int add_string_tab);
#endif /* _LIBFDT_H */