libc: minimal: implement putc_unlocked & putchar_unlocked

Add a simple implementation for putc_unlocked() &
putchar_unlocked().

Signed-off-by: Yong Cong Sin <ycsin@meta.com>

doc/services/portability/posix/option_groups/index.rst

@@ -569,8 +569,8 @@ This table lists service support status in Zephyr for `POSIX_FD_MGMT`:
     funlockfile(), yes
     getc_unlocked(),
     getchar_unlocked(),
-    putc_unlocked(),
-    putchar_unlocked(),
+    putc_unlocked(), yes
+    putchar_unlocked(), yes
 
 .. _posix_option_group_memory_protection:
 

lib/libc/Kconfig

@@ -76,6 +76,8 @@ config MINIMAL_LIBC
 	imply COMMON_LIBC_CALLOC
 	imply COMMON_LIBC_REALLOCARRAY
 	select POSIX_FILE_LOCKING if POSIX_THREAD_SAFE_FUNCTIONS
+	select COMMON_LIBC_PUTC_UNLOCKED if POSIX_THREAD_SAFE_FUNCTIONS
+	select COMMON_LIBC_GETC_UNLOCKED if POSIX_THREAD_SAFE_FUNCTIONS
 	help
 	  Build with minimal C library.
 

lib/libc/common/CMakeLists.txt

@@ -17,5 +17,7 @@ zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_THRD
     source/thrd/tss.c
     )
 
+add_subdirectory(source)
+
 # Prevent compiler from optimizing calloc into an infinite recursive call
 zephyr_library_compile_options($<TARGET_PROPERTY:compiler,no_builtin_malloc>)

lib/libc/common/Kconfig

@@ -82,3 +82,5 @@ config COMMON_LIBC_THRD
 	default y
 	help
 	  Common implementation of C11 <threads.h> API.
+
+rsource "source/Kconfig"

lib/libc/common/source/CMakeLists.txt

@@ -0,0 +1,4 @@
+# Copyright (c) 2024 Meta Platforms
+# SPDX-License-Identifier: Apache-2.0
+
+add_subdirectory_ifdef(CONFIG_COMMON_LIBC_STDIO stdio)

lib/libc/common/source/Kconfig

@@ -0,0 +1,4 @@
+# Copyright (c) 2024 Meta Platforms
+# SPDX-License-Identifier: Apache-2.0
+
+rsource "stdio/Kconfig"

lib/libc/common/source/stdio/CMakeLists.txt

@@ -0,0 +1,5 @@
+# Copyright (c) 2024 Meta Platforms
+# SPDX-License-Identifier: Apache-2.0
+
+zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_GETC_UNLOCKED getc_unlocked.c)
+zephyr_library_sources_ifdef(CONFIG_COMMON_LIBC_PUTC_UNLOCKED putc_unlocked.c)

lib/libc/common/source/stdio/Kconfig

@@ -0,0 +1,19 @@
+# Copyright (c) 2024 Meta Platforms
+# SPDX-License-Identifier: Apache-2.0
+
+config COMMON_LIBC_STDIO
+	bool
+	help
+	  common function implementation in stdio.h
+
+config COMMON_LIBC_GETC_UNLOCKED
+	bool
+	select COMMON_LIBC_STDIO
+	help
+	  common implementation of getc_unlocked() & getchar_unlocked().
+
+config COMMON_LIBC_PUTC_UNLOCKED
+	bool
+	select COMMON_LIBC_STDIO
+	help
+	  common implementation of putc_unlocked() & putchar_unlocked().

lib/libc/common/source/stdio/getc_unlocked.c

@@ -0,0 +1,24 @@
+/*
+ * Copyright (c) 2024 Meta Platforms
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <errno.h>
+#include <stdio.h>
+
+#include <zephyr/sys/util.h>
+
+int getc_unlocked(FILE *stream)
+{
+	ARG_UNUSED(stream);
+
+	errno = ENOSYS;
+
+	return EOF;
+}
+
+int getchar_unlocked(void)
+{
+	return getc_unlocked(stdin);
+}

lib/libc/common/source/stdio/putc_unlocked.c

@@ -0,0 +1,19 @@
+/*
+ * Copyright (c) 2024 Meta Platforms
+ *
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+#include <stdio.h>
+
+#include <zephyr/sys/libc-hooks.h>
+
+int putc_unlocked(int c, FILE *stream)
+{
+	return zephyr_fputc(c, stream);
+}
+
+int putchar_unlocked(int c)
+{
+	return putc_unlocked(c, stdout);
+}

lib/libc/minimal/include/stdio.h

@@ -63,6 +63,11 @@ size_t fwrite(const void *ZRESTRICT ptr, size_t size, size_t nitems,
 #define putc(c, stream) fputc(c, stream)
 #define putchar(c) putc(c, stdout)
 
+#if defined(CONFIG_COMMON_LIBC_PUTC_UNLOCKED) || defined(__DOXYGEN__)
+int putc_unlocked(int c, FILE *stream);
+int putchar_unlocked(int c);
+#endif /* CONFIG_COMMON_LIBC_PUTC_UNLOCKED || __DOXYGEN__ */
+
 #if defined(CONFIG_POSIX_FILE_LOCKING) || defined(__DOXYGEN__)
 void flockfile(FILE *file);
 int ftrylockfile(FILE *file);

lib/posix/options/file_locking.c

@@ -6,6 +6,7 @@
 
 #include <stdio.h>
 
+#include <zephyr/sys/libc-hooks.h>
 #include <zephyr/sys/util.h>
 
 void zvfs_flockfile(int fd);

tests/posix/common/src/file_locking.c

@@ -102,6 +102,49 @@ ZTEST(file_locking, test_file_locking)
 	z_free_fd(POINTER_TO_INT(file));
 }
 
+void put_thread(void *p1, void *p2, void *p3)
+{
+	FILE *file = p1;
+
+	/* Lock held in main thread */
+	zassert_not_ok(ftrylockfile(file));
+
+	/* Wait for the lock */
+	flockfile(file);
+	zassert_equal(putc_unlocked('S', file), 'S');
+	zassert_equal(putchar('T'), 'T');
+	funlockfile(file);
+}
+
+ZTEST(file_locking, test_stdio)
+{
+	FILE *file = INT_TO_POINTER(z_alloc_fd(NULL, NULL));
+	struct k_thread test_thread;
+	int priority = k_thread_priority_get(k_current_get());
+
+	/* Lock the file before creating the test thread */
+	flockfile(file);
+
+	k_thread_create(&test_thread, test_stack, K_THREAD_STACK_SIZEOF(test_stack),
+			put_thread, file, INT_TO_POINTER(true), NULL, priority, 0,
+			K_NO_WAIT);
+
+	/* Allow the test thread to run */
+	k_msleep(100);
+	/* The test thread should be waiting for the lock */
+	zassert_equal(k_thread_join(&test_thread, K_MSEC(10)), -EAGAIN);
+
+	/* Main thread has the lock, either version should work */
+	zassert_equal(putc('T', file), 'T');
+	zassert_equal(putchar_unlocked('E'), 'E');
+
+	/* We are done with the file here, unlock it so that test thread can run */
+	funlockfile(file);
+	zassert_equal(k_thread_join(&test_thread, K_MSEC(100)), 0);
+
+	z_free_fd(POINTER_TO_INT(file));
+}
+
 #else
 /**
  * PicoLIBC doesn't support these functions in its header