[PATCH v2 0/2] Add strprefix() and fix a bug with it
From: Alejandro Colomar
Date: Thu Nov 05 2026 - 08:03:39 EST
Hi!
str_has_prefix() is based on sizes and lengths, which means it must
overload the valid length 0 to mean not found. This is a typical
consequence of choosing to design an API around sizes and lengths, and
vanishes when moving to pointer-based similar APIs.
This patch set adds strprefix(), deprecates str_has_prefix(), and uses
strprefix() in one place to fix a bug reported by Bartosz.
We can later work on replacing the other uses of str_has_prefix(), which
might hide similar bugs.
Changes in v2
~~~~~~~~~~~~~
- Added tests, as suggested by Andy.
- Remove Cc tags from the commit messages. [Andy]
Testing
~~~~~~~
The new tests added for strprefix() pass. Below is the session I ran
for testing. The important line is:
[13:26:30] [PASSED] string_test_strprefix
Full session:
$ cat .kunitconfig
CONFIG_KUNIT=y
CONFIG_STRING_KUNIT_TEST=y
$ mkdir -p ~/tmp
$ export TMPDIR=$HOME/tmp
$ ./tools/testing/kunit/kunit.py run "string*"
[13:26:28] Configuring KUnit Kernel ...
[13:26:28] Building KUnit Kernel ...
Populating config with:
$ make ARCH=um O=.kunit olddefconfig
Building with:
$ make all compile_commands.json scripts_gdb ARCH=um O=.kunit --jobs=24
[13:26:30] Starting KUnit Kernel (1/1)...
[13:26:30] ============================================================
Running tests with:
$ .kunit/linux 'kunit.filter_glob=string*' kunit.enable=1 mem=1G console=tty kunit_shutdown=halt
[13:26:30] ============= string-stream-test (12 subtests) =============
[13:26:30] [PASSED] string_stream_managed_init_test
[13:26:30] [PASSED] string_stream_unmanaged_init_test
[13:26:30] [PASSED] string_stream_managed_free_test
[13:26:30] [PASSED] string_stream_resource_free_test
[13:26:30] [PASSED] string_stream_line_add_test
[13:26:30] [PASSED] string_stream_variable_length_line_test
[13:26:30] [PASSED] string_stream_append_test
[13:26:30] [PASSED] string_stream_append_auto_newline_test
[13:26:30] [PASSED] string_stream_append_empty_string_test
[13:26:30] [PASSED] string_stream_no_auto_newline_test
[13:26:30] [PASSED] string_stream_auto_newline_test
[13:26:30] [PASSED] string_stream_performance_test
[13:26:30] =============== [PASSED] string-stream-test ================
[13:26:30] =================== string (29 subtests) ===================
[13:26:30] [PASSED] string_test_memset16
[13:26:30] [PASSED] string_test_memset32
[13:26:30] [PASSED] string_test_memset64
[13:26:30] [PASSED] string_test_strlen
[13:26:30] [PASSED] string_test_strnlen
[13:26:30] [PASSED] string_test_strchr
[13:26:30] [PASSED] string_test_strnchr
[13:26:30] [PASSED] string_test_strrchr
[13:26:30] [PASSED] string_test_strspn
[13:26:30] [PASSED] string_test_strprefix
[13:26:30] [PASSED] string_test_strcmp
[13:26:30] [PASSED] string_test_strcmp_long_strings
[13:26:30] [PASSED] string_test_strncmp
[13:26:30] [PASSED] string_test_strncmp_long_strings
[13:26:30] [PASSED] string_test_strcasecmp
[13:26:30] [PASSED] string_test_strcasecmp_long_strings
[13:26:30] [PASSED] string_test_strncasecmp
[13:26:30] [PASSED] string_test_strncasecmp_long_strings
[13:26:30] [PASSED] string_test_strscpy
[13:26:30] [PASSED] string_test_strcat
[13:26:30] [PASSED] string_test_strncat
[13:26:30] [PASSED] string_test_strlcat
[13:26:30] [PASSED] string_test_strtomem
[13:26:30] [PASSED] string_test_memtostr
[13:26:30] [PASSED] string_test_strends
[13:26:30] [SKIPPED] string_bench_strlen (not enabled)
[13:26:30] [SKIPPED] string_bench_strnlen (not enabled)
[13:26:30] [SKIPPED] string_bench_strchr (not enabled)
[13:26:30] [SKIPPED] string_bench_strrchr (not enabled)
[13:26:30] ===================== [PASSED] string ======================
[13:26:30] =============== string_helpers (4 subtests) ================
[13:26:30] [PASSED] test_get_size
[13:26:30] [PASSED] test_upper_lower
[13:26:30] [PASSED] test_unescape
[13:26:30] [PASSED] test_escape
[13:26:30] ================= [PASSED] string_helpers ==================
[13:26:30] ============================================================
[13:26:30] Testing complete. Ran 45 tests: passed: 41, skipped: 4
[13:26:31] Elapsed time: 2.509s total, 0.001s configuring, 2.192s building, 0.271s running
Cheers,
Alex
Alejandro Colomar (2):
string: Add strprefix(), and deprecate str_has_prefix()
device property: Fix fwnode_name_eq() for empty node names
drivers/base/property.c | 5 +----
include/linux/string.h | 19 ++++++++++++++++++-
lib/tests/string_kunit.c | 9 +++++++++
3 files changed, 28 insertions(+), 5 deletions(-)
Range-diff against v1:
1: 9c81f6f62fd0 ! 1: d3b325ecefd1 string: Add strprefix(), and deprecate str_has_prefix()
@@ Commit message
We'll slowly migrate existing code from str_has_prefix() to strprefix().
Reported-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>
- Cc: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
- Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Andy Shevchenko <andy@xxxxxxxxxx>
- Cc: Bartosz Golaszewski <brgl@xxxxxxxxxx>
- Cc: Daniel Scally <djrscally@xxxxxxxxx>
- Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
- Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
- Cc: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
- Cc: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
- Cc: Joe Perches <joe@xxxxxxxxxxx>
- Cc: Johan Hovold <johan@xxxxxxxxxx>
- Cc: Kees Cook <kees@xxxxxxxxxx>
- Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
- Cc: Len Brown <lenb@xxxxxxxxxx>
- Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Cc: Linus Walleij <linusw@xxxxxxxxxx>
- Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
- Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
- Cc: Rob Herring <robh@xxxxxxxxxx>
- Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
- Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
- Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
- Cc: Tom Zanussi <zanussi@xxxxxxxxxx
- Cc: linux-acpi@xxxxxxxxxxxxxxx
- Cc: driver-core@xxxxxxxxxxxxxxx
- Cc: linux-kernel@xxxxxxxxxxxxxxx
- Cc: linux-hardening@xxxxxxxxxxxxxxx
- Cc: devicetree@xxxxxxxxxxxxxxx
- Cc: linux-gpio@xxxxxxxxxxxxxxx
Signed-off-by: Alejandro Colomar <alx@xxxxxxxxxx>
## include/linux/string.h ##
@@ include/linux/string.h: void memcpy_and_pad(void *dest, size_t dest_len, const v
*
* Returns:
* * strlen(@prefix) if @str starts with @prefix
+
+ ## lib/tests/string_kunit.c ##
+@@ lib/tests/string_kunit.c: static void string_test_strspn(struct kunit *test)
+ }
+ }
+
++static void string_test_strprefix(struct kunit *test)
++{
++ KUNIT_ASSERT_EQ(test, 0, strcmp(strprefix("foobar", "foo"), "bar"));
++ KUNIT_ASSERT_EQ(test, 0, strcmp(strprefix("foobar", ""), "foobar"));
++ KUNIT_ASSERT_EQ(test, 0, strcmp(strprefix("foobar", "foobar"), ""));
++ KUNIT_ASSERT_NULL(test, strprefix("foobar", "bar"));
++}
++
+ static char strcmp_buffer1[STRCMP_LARGE_BUF_LEN];
+ static char strcmp_buffer2[STRCMP_LARGE_BUF_LEN];
+
+@@ lib/tests/string_kunit.c: static struct kunit_case string_test_cases[] = {
+ KUNIT_CASE(string_test_strnchr),
+ KUNIT_CASE(string_test_strrchr),
+ KUNIT_CASE(string_test_strspn),
++ KUNIT_CASE(string_test_strprefix),
+ KUNIT_CASE(string_test_strcmp),
+ KUNIT_CASE(string_test_strcmp_long_strings),
+ KUNIT_CASE(string_test_strncmp),
2: 37eafcd682b0 ! 2: ac9728afa027 device property: Fix fwnode_name_eq() for empty node names
@@ Commit message
Fixes: a9c8c738066b7 ("device property: Add fwnode_name_eq()")
Reported-by: Bartosz Golaszewski <bartosz.golaszewski@xxxxxxxxxxxxxxxx>
- Cc: Andreas Schwab <schwab@xxxxxxxxxxxxxx>
- Cc: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Cc: Andy Shevchenko <andy@xxxxxxxxxx>
- Cc: Bartosz Golaszewski <brgl@xxxxxxxxxx>
- Cc: Daniel Scally <djrscally@xxxxxxxxx>
- Cc: Danilo Krummrich <dakr@xxxxxxxxxx>
- Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
- Cc: Hans Verkuil <hverkuil-cisco@xxxxxxxxx>
- Cc: Heikki Krogerus <heikki.krogerus@xxxxxxxxxxxxxxx>
- Cc: Joe Perches <joe@xxxxxxxxxxx>
- Cc: Johan Hovold <johan@xxxxxxxxxx>
- Cc: Kees Cook <kees@xxxxxxxxxx>
- Cc: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
- Cc: Len Brown <lenb@xxxxxxxxxx>
- Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
- Cc: Linus Walleij <linusw@xxxxxxxxxx>
- Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
- Cc: "Rafael J. Wysocki" <rafael@xxxxxxxxxx>
- Cc: Rob Herring <robh@xxxxxxxxxx>
- Cc: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
- Cc: Saravana Kannan <saravanak@xxxxxxxxxx>
- Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
- Cc: Tom Zanussi <zanussi@xxxxxxxxxx
- Cc: linux-acpi@xxxxxxxxxxxxxxx
- Cc: driver-core@xxxxxxxxxxxxxxx
- Cc: linux-kernel@xxxxxxxxxxxxxxx
- Cc: linux-hardening@xxxxxxxxxxxxxxx
- Cc: devicetree@xxxxxxxxxxxxxxx
- Cc: linux-gpio@xxxxxxxxxxxxxxx
Signed-off-by: Alejandro Colomar <alx@xxxxxxxxxx>
## drivers/base/property.c ##
--
2.55.0
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