[PATCH v2 1/2] pylibfdt: Add a method to access the device tree directly

[PATCH v2 1/2] pylibfdt: Add a method to access the device tree directly

[Simon Glass]

When calling libfdt functions which are not supported by the Fdt class it
is necessary to get direct access to the device tree data. At present this
requries using the internal _fdt member. Add a new method to provide
public access to this.

Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
---

Changes in v2:
- Change from get_fdt() to as_bytearray()

 pylibfdt/libfdt.i       | 11 +++++++++++
 tests/pylibfdt_tests.py |  5 +++--
 2 files changed, 14 insertions(+), 2 deletions(-)

diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
index 415820d..f8e3a2c 100644
--- a/pylibfdt/libfdt.i
+++ b/pylibfdt/libfdt.i
@@ -174,6 +174,17 @@ class Fdt:
         self._fdt = bytearray(data)
         check_err(fdt_check_header(self._fdt));
 
+    def as_bytearray(self):
+        """Get the device tree contents as a bytearray
+
+        This can be passed directly to libfdt functions that access a
+        const void * for the device tree.
+
+        Returns:
+            bytearray containing the device tree
+        """
+        return self._fdt
+
     def subnode_offset(self, parentoffset, name, quiet=()):
         """Get the offset of a named subnode
 
diff --git a/tests/pylibfdt_tests.py b/tests/pylibfdt_tests.py
index 95d911a..0ec0f38 100644
--- a/tests/pylibfdt_tests.py
+++ b/tests/pylibfdt_tests.py
@@ -297,9 +297,10 @@ class PyLibfdtTests(unittest.TestCase):
 
     def testIntegers(self):
         """Check that integers can be passed and returned"""
-        self.assertEquals(0, libfdt.fdt_get_phandle(self.fdt._fdt, 0))
+        self.assertEquals(0, libfdt.fdt_get_phandle(self.fdt.as_bytearray(), 0))
         node2 = self.fdt.path_offset('/subnode@2')
-        self.assertEquals(0x2000, libfdt.fdt_get_phandle(self.fdt._fdt, node2))
+        self.assertEquals(
+                0x2000, libfdt.fdt_get_phandle(self.fdt.as_bytearray(), node2))
 
     def testGetPhandle(self):
         """Test for the get_phandle() method"""
-- 
2.14.1.581.gf28d330327-goog

[PATCH v2 2/2] pylibfdt: Allow reading integer values from properties

[Simon Glass]

Extend the Properties class with some functions to read a single integer
property. Add a new getprop_obj() function to return a Property object
instead of the raw data.

This suggested approach can be extended to handle other types, as well as
arrays.

Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
---

Changes in v2: None

 pylibfdt/libfdt.i       | 35 +++++++++++++++++++++++++++++++++++
 tests/pylibfdt_tests.py | 12 ++++++++++++
 tests/run_tests.sh      |  1 +
 tests/test_props.dts    | 11 +++++++++++
 4 files changed, 59 insertions(+)
 create mode 100644 tests/test_props.dts

diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
index f8e3a2c..4d60f90 100644
--- a/pylibfdt/libfdt.i
+++ b/pylibfdt/libfdt.i
@@ -376,6 +376,26 @@ class Fdt:
             return pdata
         return bytearray(pdata[0])
 
+    def getprop_obj(self, nodeoffset, prop_name, quiet=()):
+        """Get a property from a node as a Property object
+
+        Args:
+            nodeoffset: Node offset containing property to get
+            prop_name: Name of property to get
+            quiet: Errors to ignore (empty to raise on all errors)
+
+        Returns:
+            Property object, or None if not found
+
+        Raises:
+            FdtError if any error occurs (e.g. the property is not found)
+        """
+        pdata = check_err_null(fdt_getprop(self._fdt, nodeoffset, prop_name),
+                               quiet)
+        if isinstance(pdata, (int)):
+            return None
+        return Property(prop_name, bytearray(pdata[0]))
+
     def get_phandle(self, nodeoffset):
         """Get the phandle of a node
 
@@ -432,6 +452,21 @@ class Property:
     def __init__(self, name, value):
         self.name = name
         self.value = value
+
+    def to_cell(self, fmt):
+        return struct.unpack('>' + fmt, self.value)[0]
+
+    def to_uint32(self):
+        return self.to_cell('L')
+
+    def to_int32(self):
+        return self.to_cell('l')
+
+    def to_uint64(self):
+        return self.to_cell('Q')
+
+    def to_int64(self):
+        return self.to_cell('q')
 %}
 
 %rename(fdt_property) fdt_property_func;
diff --git a/tests/pylibfdt_tests.py b/tests/pylibfdt_tests.py
index 0ec0f38..fc5210b 100644
--- a/tests/pylibfdt_tests.py
+++ b/tests/pylibfdt_tests.py
@@ -89,6 +89,7 @@ class PyLibfdtTests(unittest.TestCase):
     def setUp(self):
         """Read in the device tree we use for testing"""
         self.fdt = _ReadFdt('test_tree1.dtb')
+        self.fdt2 = _ReadFdt('test_props.dtb')
 
     def GetPropList(self, node_path):
         """Read a list of properties from a node
@@ -330,6 +331,17 @@ class PyLibfdtTests(unittest.TestCase):
         node2 = self.fdt.path_offset('/subnode@2/subsubnode@0')
         self.assertEquals(node2, self.fdt.node_offset_by_phandle(0x2001))
 
+    def get_prop(self, name):
+        return self.fdt2.getprop_obj(0, name)
+
+    def testGetIntProperties(self):
+        """Test that we can access properties as integers"""
+        self.assertEquals(0xdeadbeef, self.get_prop("prop-hex32").to_uint32())
+        self.assertEquals(123, self.get_prop("prop-uint32").to_uint32())
+        self.assertEquals(-2, self.get_prop("prop-int32").to_int32())
+        self.assertEquals(9223372036854775807,
+                          self.get_prop("prop-uint64").to_uint64())
+        self.assertEquals(-2, self.get_prop("prop-int64").to_int64())
 
 if __name__ == "__main__":
     unittest.main()
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index fa7b2f7..441e773 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -809,6 +809,7 @@ fdtoverlay_tests() {
 }
 
 pylibfdt_tests () {
+    run_dtc_test -I dts -O dtb -o test_props.dtb test_props.dts
     TMP=/tmp/tests.stderr.$$
     python pylibfdt_tests.py -v 2> $TMP
 
diff --git a/tests/test_props.dts b/tests/test_props.dts
new file mode 100644
index 0000000..7e59bd1
--- /dev/null
+++ b/tests/test_props.dts
@@ -0,0 +1,11 @@
+/dts-v1/;
+
+/ {
+	compatible = "test_props";
+	prop-hex32 = <0xdeadbeef>;
+	prop-uint32 = <123>;
+	prop-int32 = <0xfffffffe>;
+	prop-hex64 = /bits/ 64 <0xdeadbeef01abcdef>;
+	prop-uint64 = /bits/ 64 <9223372036854775807>;
+	prop-int64 = /bits/ 64 <0xfffffffffffffffe>;
+};
-- 
2.14.1.581.gf28d330327-goog

Re: [PATCH v2 1/2] pylibfdt: Add a method to access the device tree directly

[David Gibson]

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On Thu, Aug 31, 2017 at 04:41:59AM -0600, Simon Glass wrote:
> When calling libfdt functions which are not supported by the Fdt class it
> is necessary to get direct access to the device tree data. At present this
> requries using the internal _fdt member. Add a new method to provide
> public access to this.
> 
> Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>

Sorry I've taken so long to look at this.

I don't think this actually has much value.  You're directly returning
_fdt, which is a mutable object.  Anything bad you can do to the
object by accessing _fdt directly you can do just as badly via this
method.

Which makes this an abstraction that doesn't abstract, and an
interface that doesn't actually protect anything, even notionally.

If you want things from outside to be able to access the raw blob, I
suggest you just remove the underscore and make .fdt an advertised,
accessible attribute of the object.



> ---
> 
> Changes in v2:
> - Change from get_fdt() to as_bytearray()
> 
>  pylibfdt/libfdt.i       | 11 +++++++++++
>  tests/pylibfdt_tests.py |  5 +++--
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
> index 415820d..f8e3a2c 100644
> --- a/pylibfdt/libfdt.i
> +++ b/pylibfdt/libfdt.i
> @@ -174,6 +174,17 @@ class Fdt:
>          self._fdt = bytearray(data)
>          check_err(fdt_check_header(self._fdt));
>  
> +    def as_bytearray(self):
> +        """Get the device tree contents as a bytearray
> +
> +        This can be passed directly to libfdt functions that access a
> +        const void * for the device tree.
> +
> +        Returns:
> +            bytearray containing the device tree
> +        """
> +        return self._fdt
> +
>      def subnode_offset(self, parentoffset, name, quiet=()):
>          """Get the offset of a named subnode
>  
> diff --git a/tests/pylibfdt_tests.py b/tests/pylibfdt_tests.py
> index 95d911a..0ec0f38 100644
> --- a/tests/pylibfdt_tests.py
> +++ b/tests/pylibfdt_tests.py
> @@ -297,9 +297,10 @@ class PyLibfdtTests(unittest.TestCase):
>  
>      def testIntegers(self):
>          """Check that integers can be passed and returned"""
> -        self.assertEquals(0, libfdt.fdt_get_phandle(self.fdt._fdt, 0))
> +        self.assertEquals(0, libfdt.fdt_get_phandle(self.fdt.as_bytearray(), 0))
>          node2 = self.fdt.path_offset('/subnode@2')
> -        self.assertEquals(0x2000, libfdt.fdt_get_phandle(self.fdt._fdt, node2))
> +        self.assertEquals(
> +                0x2000, libfdt.fdt_get_phandle(self.fdt.as_bytearray(), node2))
>  
>      def testGetPhandle(self):
>          """Test for the get_phandle() method"""

-- 
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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Re: [PATCH v2 2/2] pylibfdt: Allow reading integer values from properties

[David Gibson]

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On Thu, Aug 31, 2017 at 04:42:00AM -0600, Simon Glass wrote:
> Extend the Properties class with some functions to read a single integer
> property. Add a new getprop_obj() function to return a Property object
> instead of the raw data.
> 
> This suggested approach can be extended to handle other types, as well as
> arrays.
> 
> Signed-off-by: Simon Glass <sjg-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>

Sorry again I've taken so long to respond.

This way of doing it really seems awkward to me.  You're introducing a
clunky variant getter just to wrap the bytearray in an object,
essentially just to get conversion methods.

It seems to be simpler to just have as_cell() and whatnot as plain
functions that go straight from bytestring/bytearray to an int or
whatever.


Longer term, I did have an idea that might resolve the
propery-as-object or property-as-bytestring conundrum a bit more
satisfactorily.  But, I'm not entirely sure how you'd go about
implementing it with swig in the picture: it should be possible in
(modern) Python to make a Property object that's a sub-class of the
(byte)string type.  That way it can be used directly as though it were
a bytestring, but you can also add properties to do extra stuff.

[Which raises a minor detail, most of the functions which return
bytearray()s now should probably be returning strings - there doesn't
seem to be a reason to return a mutable object]
> ---
> 
> Changes in v2: None
> 
>  pylibfdt/libfdt.i       | 35 +++++++++++++++++++++++++++++++++++
>  tests/pylibfdt_tests.py | 12 ++++++++++++
>  tests/run_tests.sh      |  1 +
>  tests/test_props.dts    | 11 +++++++++++
>  4 files changed, 59 insertions(+)
>  create mode 100644 tests/test_props.dts
> 
> diff --git a/pylibfdt/libfdt.i b/pylibfdt/libfdt.i
> index f8e3a2c..4d60f90 100644
> --- a/pylibfdt/libfdt.i
> +++ b/pylibfdt/libfdt.i
> @@ -376,6 +376,26 @@ class Fdt:
>              return pdata
>          return bytearray(pdata[0])
>  
> +    def getprop_obj(self, nodeoffset, prop_name, quiet=()):
> +        """Get a property from a node as a Property object
> +
> +        Args:
> +            nodeoffset: Node offset containing property to get
> +            prop_name: Name of property to get
> +            quiet: Errors to ignore (empty to raise on all errors)
> +
> +        Returns:
> +            Property object, or None if not found
> +
> +        Raises:
> +            FdtError if any error occurs (e.g. the property is not found)
> +        """
> +        pdata = check_err_null(fdt_getprop(self._fdt, nodeoffset, prop_name),
> +                               quiet)
> +        if isinstance(pdata, (int)):
> +            return None
> +        return Property(prop_name, bytearray(pdata[0]))
> +
>      def get_phandle(self, nodeoffset):
>          """Get the phandle of a node
>  
> @@ -432,6 +452,21 @@ class Property:
>      def __init__(self, name, value):
>          self.name = name
>          self.value = value
> +
> +    def to_cell(self, fmt):
> +        return struct.unpack('>' + fmt, self.value)[0]
> +
> +    def to_uint32(self):
> +        return self.to_cell('L')
> +
> +    def to_int32(self):
> +        return self.to_cell('l')
> +
> +    def to_uint64(self):
> +        return self.to_cell('Q')
> +
> +    def to_int64(self):
> +        return self.to_cell('q')
>  %}
>  
>  %rename(fdt_property) fdt_property_func;
> diff --git a/tests/pylibfdt_tests.py b/tests/pylibfdt_tests.py
> index 0ec0f38..fc5210b 100644
> --- a/tests/pylibfdt_tests.py
> +++ b/tests/pylibfdt_tests.py
> @@ -89,6 +89,7 @@ class PyLibfdtTests(unittest.TestCase):
>      def setUp(self):
>          """Read in the device tree we use for testing"""
>          self.fdt = _ReadFdt('test_tree1.dtb')
> +        self.fdt2 = _ReadFdt('test_props.dtb')
>  
>      def GetPropList(self, node_path):
>          """Read a list of properties from a node
> @@ -330,6 +331,17 @@ class PyLibfdtTests(unittest.TestCase):
>          node2 = self.fdt.path_offset('/subnode@2/subsubnode@0')
>          self.assertEquals(node2, self.fdt.node_offset_by_phandle(0x2001))
>  
> +    def get_prop(self, name):
> +        return self.fdt2.getprop_obj(0, name)
> +
> +    def testGetIntProperties(self):
> +        """Test that we can access properties as integers"""
> +        self.assertEquals(0xdeadbeef, self.get_prop("prop-hex32").to_uint32())
> +        self.assertEquals(123, self.get_prop("prop-uint32").to_uint32())
> +        self.assertEquals(-2, self.get_prop("prop-int32").to_int32())
> +        self.assertEquals(9223372036854775807,
> +                          self.get_prop("prop-uint64").to_uint64())
> +        self.assertEquals(-2, self.get_prop("prop-int64").to_int64())
>  
>  if __name__ == "__main__":
>      unittest.main()
> diff --git a/tests/run_tests.sh b/tests/run_tests.sh
> index fa7b2f7..441e773 100755
> --- a/tests/run_tests.sh
> +++ b/tests/run_tests.sh
> @@ -809,6 +809,7 @@ fdtoverlay_tests() {
>  }
>  
>  pylibfdt_tests () {
> +    run_dtc_test -I dts -O dtb -o test_props.dtb test_props.dts
>      TMP=/tmp/tests.stderr.$$
>      python pylibfdt_tests.py -v 2> $TMP
>  
> diff --git a/tests/test_props.dts b/tests/test_props.dts
> new file mode 100644
> index 0000000..7e59bd1
> --- /dev/null
> +++ b/tests/test_props.dts
> @@ -0,0 +1,11 @@
> +/dts-v1/;
> +
> +/ {
> +	compatible = "test_props";
> +	prop-hex32 = <0xdeadbeef>;
> +	prop-uint32 = <123>;
> +	prop-int32 = <0xfffffffe>;
> +	prop-hex64 = /bits/ 64 <0xdeadbeef01abcdef>;
> +	prop-uint64 = /bits/ 64 <9223372036854775807>;
> +	prop-int64 = /bits/ 64 <0xfffffffffffffffe>;
> +};

-- 
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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