[PATCH v2 0/3] Introduce fdtgrep for subsetting and hashing FDTs

[Simon Glass]

This series adds two new functions, fdt_first_region() and
fdt_next_regions() which map FDT parts such as nodes and properties to
their regions in the FDT binary. The function is then used to implement
a grep utility for FDTs.

The core core is quite simple and small, but it grew a little due
to the need to make it iterative (first/next/next). Also this series adds
tests and a grep utility, so quite a bit of code is built on it.

The use for this feature is twofold. Firstly it provides a convenient
way of performing a structure-aware grep of the tree. For example it is
possible to grep for a node and get all the properties associated with
that node. Trees can be subsetted easily, by specifying the nodes that
are required, and then writing out the regions returned by this function.
This is useful for small resource-constrained systems, such as boot
loaders, which want to use an FDT but do not need to know about all of
it. The full FDT can be grepped to pull out the few things that are
needed - this can be automatic and does not require the FDT source code.

This first use makes it easy to implement an FDT grep. Options are
provided to search for matching nodes (by name or compatible string),
properties and also for any of the above. It is possible to search for
non-matches also (useful for excluding a particular property from the
FDT, for example). The output is like fdtdump, but only with the regions
selected by the grep. Options are also provided to print the string table,
memory reservation table, etc. The fdtgrep utility can output valid
source, which can be used by dtc, but it can also directly output a new
.dtb binary.

Secondly it makes it easy to hash parts of the tree and detect changes.
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.
An assumption is made here that the tree ordering remains the same.

This second use is the subject of a recent series sent to the U-Boot
mailing list, to enhance FIT images to support verified boot. Briefly,
this works by signing configurations (consisting of particular kernel
and FDT combinations) so that the boot loader can verify that these
combinations are valid and permitted. Since a FIT image is in fact an
FDT, we need to be able to hash particular regions of the FDT for the
signing and verification process. This is done by using the region functions
to select the data that needs to be hashed for a particular configuration.

The fdtgrep utility could be used to replace all of the functions of
fdtdump. However fdtdump is intended as a separate, simple way of
dumping the tree (for verifying against dtc output for example). So
fdtdump remains a separate program and this series leaves it alone.

Note: a somewhat unfortunately feature of this implementation is that
a state structure needs to be kept around between calls of
fdt_next_region(). This is declared in libfdt.h but really should be
opaque.

Changes in v2:
- Move region code to separate fdt_region.c file
- Fix info->count <= info->max_regions in fdt_add_region() merge case
- Add new FDT_ERR_TOODEEP error type and use it
- Change returned error from BADLAYOUT to BADSTRUCTURE
- Return FDT_ERR_BADLAYOUT error if strings block is before structure block
- Add note that changes in node/property order can cause false hash misses
- Add more comments about the -1 return value from h_include
- Drop FDT_IS_COMPAT and pass node offset to h_include function
- Drop stale comment about names / wildcards
- Move to a model with fdt_first_region()/fdt_next_region()
- Add long comment explaining theory of operation
- Add local fdt_find_regions() function since libfdt no longer has it
- Drop patch to replace fdtdump

Simon Glass (3):
  libfdt: Add function to find regions in an FDT
  Add fdtgrep to grep and subset FDTs
  RFC: Check offset in fdt_string()

 .gitignore             |   1 +
 Makefile               |   4 +
 Makefile.utils         |   7 +
 fdtgrep.c              | 838 +++++++++++++++++++++++++++++++++++++++++++++++++
 libfdt/Makefile.libfdt |   3 +-
 libfdt/fdt_region.c    | 452 ++++++++++++++++++++++++++
 libfdt/fdt_ro.c        |   2 +
 libfdt/libfdt.h        | 213 ++++++++++++-
 tests/.gitignore       |   1 +
 tests/Makefile.tests   |   3 +-
 tests/grep.dts         |  23 ++
 tests/region_tree.c    | 336 ++++++++++++++++++++
 tests/run_tests.sh     | 353 ++++++++++++++++++++-
 tests/tests.sh         |   1 +
 14 files changed, 2233 insertions(+), 4 deletions(-)
 create mode 100644 fdtgrep.c
 create mode 100644 libfdt/fdt_region.c
 create mode 100644 tests/grep.dts
 create mode 100644 tests/region_tree.c

-- 
1.8.1.3