There is no definitive and portable way to do this. In fact, most coding standards I've worked with will not permit any structure that is defined differently based on macros, particularly if that structure is used as part of an API. This would be considered an API design flaw if an interface structure is not consistently defined.
Rather than having the structure contents actually change based on the compile time configuration, it is better to keep it consistent but rather simply set the values to something to indicate they are not used. That is, in your example, keep the function pointers unconditionally, without any "ifdef":

struct lfs_config {
    ...
    int (*lock)(const struct lfs_config *c);
    int (*unlock)(const struct lfs_config *c);
    ...
};

In the event that LFS_THREADSAFE is undefined, these pointers can be set NULL. Assuming you use c99 style initializers, this can just work, i.e.

const struct lfs_config MY_CONFIG = {
    .other_option_1 = <value>
#ifdef LFS_THREADSAFE
    .lock = my_lock
    .unlock = my_unlock
#endif
    .other_option_2 = <value>
};

In this case, if LFS_THREADSAFE is defined, the lock and unlock items will be set accordingly. But if LFS_THREADSAFE is undefined, these initializers will be omitted, and per the C99 standard, the unspecified members will be assigned value 0 (NULL, in the case of a pointer). Inside the library, it can be made to simply skip the lock/unlock call if the function pointer value is NULL.
Alternatively, one could also always set the pointer to a valid function, but have it be a no-op if the LFS_THREADSAFE is undefined. That is:

int my_lock(struct lfs_config *c)
{
#ifdef LFS_THREADSAFE
    <do_something>
#endif
    return 0;
}

And similar for unlock.
To summarize, its always wise to keep API structures as consistent as possible, and not make them dependent on macros. Hope this helps!!

我已经查看了littlefs的源代码。
LFS_THREADSAFE是 * 唯一 * 的（即，您不需要设置LFS_MIGRATE）。
只需删除lfs.h中的#ifdef/#endif即可。
但是，要回答你的问题一般来说：只需通过一个“顶级”makefile来构建您项目和littlefs：

MYPROJ = myproj
LITTLEFS = littlefs

CFLAGS += -DLFS_THREADSAFE
CFLAGS += -DLFS_NAME_MAX=367
CFLAGS := $(addprefix CFLAGS+=,$(CFLAGS))

all: lfs_mk myp_mk

myp_mk: lfs_mk
    $(MAKE) -C $(MYPROJ) $(CFLAGS) $(MAKECMDGOALS)

lfs_mk:
    $(MAKE) -C $(LITTLEFS) $(CFLAGS) $(MAKECMDGOALS)