add get_current_dir_name() api implementation

include/unistd.h

@@ -389,6 +389,7 @@ unsigned int alarm(unsigned int seconds);
 int     chdir(FAR const char *path);
 int     fchdir(int fd);
 FAR char *getcwd(FAR char *buf, size_t size);
+FAR char *get_current_dir_name(void);
 
 /* File path operations */
 

libs/libc/libc.csv

@@ -97,6 +97,7 @@
 "getaddrinfo","netdb.h","defined(CONFIG_LIBC_NETDB)","int","FAR const char *","FAR const char *","FAR const struct addrinfo *","FAR struct addrinfo **"
 "getc","stdio.h","","int","FAR FILE *"
 "getcwd","unistd.h","!defined(CONFIG_DISABLE_ENVIRON)","FAR char *","FAR char *","size_t"
+"get_current_dir_name","unistd.h","!defined(CONFIG_DISABLE_ENVIRON)","FAR char *","void"
 "getegid","unistd.h","","gid_t"
 "geteuid","unistd.h","","uid_t"
 "gethostbyname","netdb.h","defined(CONFIG_LIBC_NETDB)","FAR struct hostent *","FAR const char *"

libs/libc/unistd/lib_getcwd.c

@@ -127,3 +127,28 @@ FAR char *getcwd(FAR char *buf, size_t size)
   strlcpy(buf, pwd, size);
   return buf;
 }
+
+/****************************************************************************
+ * Name: get_current_dir_name
+ *
+ * Description:
+ *   get_current_dir_name() will allocate an buffer to hold the current
+ *   working directory info, and this buffer will be returned to user.
+ *   the user will be responsible to free the buffer.
+ *
+ * Input Parameters:
+ *   None
+ *
+ * Returned Value:
+ *   On success, get_current_dir_name() returns a pointer to a string
+ *   containing the pathname of the current working directory.
+ *   Otherwise, get_current_dir_name() returns a null pointer and
+ *   sets errno to indicate the error.
+ *   the errno can refer to: getcwd() function's comments.
+ *
+ ****************************************************************************/
+
+FAR char *get_current_dir_name(void)
+{
+  return getcwd(NULL, 0);
+}