[PATCH v3 11/15] libfdt: Introduce fdt_getprop_by_offset_w()
From: Herve Codina
Date: Wed Aug 26 2026 - 04:37:23 EST
Future operations, such as handling unknown tags on dtb modifications,
need to modify properties retrieved by their offset.
fdt_getprop_by_offset() already exists to get a preperty by its offset
but the property returned is read-only. A writable returned property is
needed.
Fill the lack and introduce fdt_getprop_by_offset_w(), the write enabled
variant of fdt_getprop_by_offset().
Add also its related test.
Signed-off-by: Herve Codina <herve.codina@xxxxxxxxxxx>
---
libfdt/libfdt.h | 6 +++
tests/.gitignore | 1 +
tests/Makefile.tests | 2 +-
tests/get_prop_offset_w.c | 84 +++++++++++++++++++++++++++++++++++++++
tests/meson.build | 1 +
tests/run_tests.sh | 1 +
tests/tests.h | 1 +
tests/testutils.c | 18 +++++++++
8 files changed, 113 insertions(+), 1 deletion(-)
create mode 100644 tests/get_prop_offset_w.c
diff --git a/libfdt/libfdt.h b/libfdt/libfdt.h
index 7a1915a5..82965e32 100644
--- a/libfdt/libfdt.h
+++ b/libfdt/libfdt.h
@@ -856,6 +856,12 @@ static inline struct fdt_property *fdt_get_property_w(void *fdt, int nodeoffset,
#ifndef SWIG /* This function is not useful in Python */
const void *fdt_getprop_by_offset(const void *fdt, int offset,
const char **namep, int *lenp);
+static inline void *fdt_getprop_by_offset_w(const void *fdt, int offset,
+ const char **namep, int *lenp)
+{
+ return (void *)(uintptr_t)fdt_getprop_by_offset(fdt, offset, namep,
+ lenp);
+}
#endif
/**
diff --git a/tests/.gitignore b/tests/.gitignore
index 69693129..1091174a 100644
--- a/tests/.gitignore
+++ b/tests/.gitignore
@@ -30,6 +30,7 @@ tmp.*
/get_phandle
/getprop
/get_prop_offset
+/get_prop_offset_w
/incbin
/integer-expressions
/fs_tree1
diff --git a/tests/Makefile.tests b/tests/Makefile.tests
index 63e201ae..0d4d399f 100644
--- a/tests/Makefile.tests
+++ b/tests/Makefile.tests
@@ -16,7 +16,7 @@ LIB_TESTS_L = get_mem_rsv \
sw_tree1 sw_states \
move_and_save mangle-layout nopulate \
open_pack rw_tree1 rw_oom set_name setprop del_property del_node \
- appendprop1 appendprop2 propname_escapes \
+ appendprop1 appendprop2 propname_escapes get_prop_offset_w \
string_escapes references path-references phandle_format \
boot-cpuid incbin relref_merge \
extra-terminating-null \
diff --git a/tests/get_prop_offset_w.c b/tests/get_prop_offset_w.c
new file mode 100644
index 00000000..dbfa5dd7
--- /dev/null
+++ b/tests/get_prop_offset_w.c
@@ -0,0 +1,84 @@
+// SPDX-License-Identifier: LGPL-2.1-or-later
+/*
+ * libfdt - Flat Device Tree manipulation
+ * Testcase for fdt_getprop_by_offset_w()
+ * Copyright (C) 2026 Bootlin.
+ */
+
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include <stdint.h>
+
+#include <libfdt.h>
+
+#include "tests.h"
+#include "testdata.h"
+
+#define SPACE 65536
+
+int main(int argc, char *argv[])
+{
+ const void *exp_val;
+ const char *name;
+ char *modif_val;
+ void *propval;
+ int proplen;
+ int exp_len;
+ int poffset;
+ void *fdt;
+ void *buf;
+ int err;
+
+ test_init(argc, argv);
+ fdt = load_blob_arg(argc, argv);
+
+ buf = xmalloc(SPACE);
+
+ err = fdt_open_into(fdt, buf, SPACE);
+ if (err)
+ FAIL("fdt_open_into(): %s", fdt_strerror(err));
+
+ free(fdt);
+ fdt = buf;
+
+ /* Retrieve the offset of the 'prop-str' property */
+ poffset = get_poffset(fdt, 0, "prop-str");
+ if (poffset < 0)
+ FAIL("Property 'prop-str' not found");
+
+ /* Get the property value for modification */
+ propval = fdt_getprop_by_offset_w(fdt, poffset, &name, &proplen);
+ if (!propval)
+ FAIL("fdt_getprop_by_offset_w(%d): %s", poffset,
+ fdt_strerror(proplen));
+
+ /* Check original values */
+ if (strcmp(name, "prop-str"))
+ FAIL("Name mismatch : %s instead of prop-str", name);
+
+ exp_len = strlen(TEST_STRING_1) + 1;
+ if (proplen != exp_len)
+ FAIL("Original size mismatch on property \"%s\": %d instead of %d",
+ name, proplen, exp_len);
+
+ exp_val = TEST_STRING_1;
+ if (memcmp(exp_val, propval, exp_len))
+ FAIL("Original data mismatch on property \"%s\"", name);
+
+ if (exp_len < 4)
+ CONFIG("Property \"%s\" should be at least 4 bytes", name);
+
+ /* Modify the property value */
+ modif_val = xmalloc(proplen);
+ memcpy(modif_val, propval, proplen);
+ modif_val[1] = (modif_val[1] != 'A') ? 'A' : 'a';
+ modif_val[3] = (modif_val[3] != 'B') ? 'B' : 'b';
+ memcpy(propval, modif_val, exp_len);
+
+ /* Check that the modified value is taken into account */
+ if (!check_get_prop_offset(fdt, poffset, "prop-str", exp_len, modif_val))
+ FAIL("Modified property 'prop-str' not found");
+
+ PASS();
+}
diff --git a/tests/meson.build b/tests/meson.build
index 779e6bc7..dae6a941 100644
--- a/tests/meson.build
+++ b/tests/meson.build
@@ -50,6 +50,7 @@ tests = [
'get_path',
'get_phandle',
'get_prop_offset',
+ 'get_prop_offset_w',
'get_next_tag_invalid_prop_len',
'getprop',
'incbin',
diff --git a/tests/run_tests.sh b/tests/run_tests.sh
index 225c22f8..419a24d8 100755
--- a/tests/run_tests.sh
+++ b/tests/run_tests.sh
@@ -419,6 +419,7 @@ tree1_tests_rw () {
run_test setprop $TREE
run_test del_property $TREE
run_test del_node $TREE
+ run_test get_prop_offset_w $TREE
}
check_tests () {
diff --git a/tests/tests.h b/tests/tests.h
index 578d8c1a..37ed3394 100644
--- a/tests/tests.h
+++ b/tests/tests.h
@@ -109,6 +109,7 @@ const void *check_get_prop_offset(void *fdt, int poffset, const char *in_name,
const void *check_getprop_addrrange(void *fdt, int parent, int nodeoffset,
const char *name, int num);
+int get_poffset(void *fdt, int nodeoffset, const char *propname);
int nodename_eq(const char *s1, const char *s2);
void vg_prepare_blob(void *fdt, size_t bufsize);
void *load_blob(const char *filename);
diff --git a/tests/testutils.c b/tests/testutils.c
index 6d69e872..d35a1978 100644
--- a/tests/testutils.c
+++ b/tests/testutils.c
@@ -230,6 +230,24 @@ const void *check_getprop_addrrange(void *fdt, int parent, int nodeoffset,
return propval;
}
+int get_poffset(void *fdt, int nodeoffset, const char *propname)
+{
+ const char *name;
+ int poffset;
+
+ fdt_for_each_property_offset(poffset, fdt, nodeoffset) {
+ if (fdt_getprop_by_offset(fdt, poffset, &name, NULL)) {
+ if (!strcmp(name, propname))
+ return poffset;
+ }
+ }
+
+ if (poffset < 0)
+ return poffset;
+
+ return -FDT_ERR_NOTFOUND;
+}
+
int nodename_eq(const char *s1, const char *s2)
{
int len = strlen(s2);
--
2.55.0