如何在 C# 中映射双 C 结构指针?

我对libACL有以下C调用：

extern int acl_get_entry(acl_t acl, int entry_id, acl_entry_t *entry_p);
extern int acl_get_permset(acl_entry_t entry_d, acl_permset_t *permset_p);

我已经跟踪了类型定义

typedef struct __acl_permset_ext *acl_permset_t;
typedef struct __acl_entry_ext  *acl_entry_t;
typedef struct __acl_ext *acl_t;

在/usr/include/acl/libacl.h 和/usr/include/sys/acl.h 中

因此，除非我犯了错误，否则这意味着上述本机调用等效于：

extern int acl_get_entry(__acl_ext *acl, int entry_id, __acl_entry_ext **entry_p);
extern int acl_get_permset(__acl_ext *entry_d, __acl_permset_ext **permset_p);

现在我对如何将这些映射到 C# 有点不知所措......
我最初以为我可以这样做：

// extern int acl_get_entry(acl_t acl, int entry_id, acl_entry_t *entry_p);
[SuppressUnmanagedCodeSecurity]
[DllImport("acl", CallingConvention = System.Runtime.InteropServices.CallingConvention.Cdecl, EntryPoint = "acl_get_entry")]
internal static extern int acl_get_entry(__acl_ext* acl, AclEntryConstants entry_id, ref __acl_entry_ext entry_p); // Double pointer, correct ???

这甚至有效，至少在表面上是有效的。
但是当我对acl_get_permset做同样的事情时

// extern int acl_get_permset(acl_entry_t entry_d, acl_permset_t *permset_p);
[SuppressUnmanagedCodeSecurity]
[DllImport("acl", CallingConvention = System.Runtime.InteropServices.CallingConvention.Cdecl,
EntryPoint = "acl_get_permset")]
internal static extern int acl_get_permset(__acl_entry_ext* entry_d, __acl_permset_ext** permset_p); // double pointer ?

即

internal static extern int acl_get_permset(__acl_entry_ext* entry_d, ref __acl_permset_ext permset_p); // double pointer ?

那就不行了...

我编写了以下 C 代码来检查：

int main()
{
// Get all the entries
acl_entry_t acl_entry_;
acl_permset_t permission_set;
acl_tag_t acl_kind_tag;
const char* _filename = "/root/Desktop/CppSharp.txt";
acl_t acl_file = acl_get_file(_filename, ACL_TYPE_ACCESS);
int found = acl_get_entry(acl_file, ACL_FIRST_ENTRY, &acl_entry_);

int a = acl_get_permset(acl_entry_, &permission_set);
int b = acl_get_tag_type(acl_entry_, &acl_kind_tag);
printf("a: %d; b: %dn", a, b);
acl_entry new_acl;
new_acl.reading = ACL_GET_PERM(permission_set, ACL_READ);
new_acl.writing = ACL_GET_PERM(permission_set, ACL_WRITE);
new_acl.execution = ACL_GET_PERM(permission_set, ACL_EXECUTE);

return 0;
}

但是我的 C# 代码执行完全相同的操作(或者我认为是这样)，可以int found = 1(就像 C 一样)，但随后它为 a 和 b 返回 -1...

static unsafe void ReadACL()
{
string fileName = "/root/Desktop/CppSharp.txt";

global::acl.__acl_ext* acl_file = NativeMethods.acl_get_file(fileName, global::acl.acl_type_t.ACL_TYPE_ACCESS);

global::acl.__acl_entry_ext acl_entry_ = new global::acl.__acl_entry_ext();
int found = NativeMethods.acl_get_entry(acl_file, global::acl.AclEntryConstants.ACL_FIRST_ENTRY, ref acl_entry_);
System.Console.WriteLine(found);

global::acl.__acl_permset_ext permission_set;
acl_tag_t acl_kind_tag = acl_tag_t.ACL_UNDEFINED_TAG;


int a = NativeMethods.acl_get_permset(&acl_entry_, &permission_set);
global::acl.acl_tag_t tag_type = acl_tag_t.ACL_UNDEFINED_TAG;
int b = NativeMethods.acl_get_tag_type(&acl_entry_, &tag_type);
System.Console.WriteLine($"{a} {b}");

另外，最奇怪的事情 - 我搜索了以下头文件：

/usr/include/acl/libacl.h 
/usr/include/sys/acl.h

以及用于__acl_permset_ext和__acl_entry_ext的整个/usr/include文件夹，但我需要谷歌它们，因为它们没有定义......C编译器是否只使用指针，根本不需要结构

？此外，在手动执行此操作之前，我尝试使用 CppSharp 自动创建绑定，但这些自动生成的绑定具有相同的问题......

mono ./CppSharp.CLI.exe --arch=x64 --output=/home/username/RiderProjects/TestProject/TestProject/AUTOMAPPED/  /usr/include/acl/libacl.h /usr/include/sys/acl.h

还有一件事我注意到： 传递双指针有什么意义？ 就像

struct x;
function(ref &x)

恕我直言，这几乎没有意义，因为您通过引用传递地址。
这些可能是数组吗？
喜欢

struct[] x;
function(ref x)

以下是常量：

// #define ACL_UNDEFINED_ID    ((id_t)-1)
// acl_check error codes
public enum acl_check_errors
: int
{
ACL_MULTI_ERROR = (0x1000), // multiple unique objects
ACL_DUPLICATE_ERROR = (0x2000), // duplicate Id's in entries
ACL_MISS_ERROR = (0x3000), // missing required entry
ACL_ENTRY_ERROR = (0x4000) // wrong entry type 
}

// 23.2.2 acl_perm_t values
public enum acl_perm_t
: uint
{
ACL_READ = (0x04),
ACL_WRITE = (0x02),
ACL_EXECUTE = (0x01),
// ACL_ADD = (0x08),
// ACL_DELETE = (0x10),
}

// 23.2.5 acl_tag_t values
public enum acl_tag_t
: int
{
ACL_UNDEFINED_TAG = (0x00),
ACL_USER_OBJ = (0x01),
ACL_USER = (0x02),
ACL_GROUP_OBJ = (0x04),
ACL_GROUP = (0x08),
ACL_MASK = (0x10),
ACL_OTHER = (0x20)
}
public enum acl_type_t
: uint
{
ACL_TYPE_ACCESS = (0x8000),
ACL_TYPE_DEFAULT = (0x4000)
}   
// 23.2.8 ACL Entry Constants
public enum AclEntryConstants
: int
{
ACL_FIRST_ENTRY = 0,
ACL_NEXT_ENTRY = 1,
}

这是我一起用谷歌搜索的结构：

// https://kernel.googlesource.com/pub/scm/fs/ext2/xfstests-bld/+/301faaf37f99fc30105f261f23d44e2a0632ffc0/acl/libacl/libobj.h
// https://kernel.googlesource.com/pub/scm/fs/ext2/xfstests-bld/+/301faaf37f99fc30105f261f23d44e2a0632ffc0/acl/libacl/libobj.h
// https://kernel.googlesource.com/pub/scm/fs/ext2/xfstests-bld/+/301faaf37f99fc30105f261f23d44e2a0632ffc0/acl/libacl/libacl.h
// https://allstar.jhuapl.edu/repo/p1/amd64/acl/libacl.h
// https://kernel.googlesource.com/pub/scm/fs/ext2/xfstests-bld/+/301faaf37f99fc30105f261f23d44e2a0632ffc0/acl/libacl/libacl.h
// https://kernel.googlesource.com/pub/scm/fs/ext2/xfstests-bld/+/301faaf37f99fc30105f261f23d44e2a0632ffc0/acl/libacl/acl_get_fd.c

[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct obj_prefix
{
public ulong p_magic;
public ulong p_flags;
}
// typedef struct __acl_permset_ext *acl_permset_t;
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct __acl_permset_ext
{
// permset_t      s_perm; // typedef unsigned int permset_t;
public uint s_perm;
};
// typedef struct acl_permset_obj_tag acl_permset_obj;
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct acl_permset_obj_tag
{
public obj_prefix o_prefix;
public __acl_permset_ext i;
};
// #define __U32_TYPE     unsigned int
// #define __ID_T_TYPE    __U32_TYPE
// __STD_TYPE __ID_T_TYPE __id_t;     /* General type for IDs.  */
// typedef __id_t id_t;
/* qualifier object */
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct __qualifier_ext
{
//id_t                    q_id;
public uint q_id;
}
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct qualifier_obj_tag
{
public obj_prefix o_prefix;
public __qualifier_ext i;
}

[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct acl_entry_obj_tag
{
public obj_prefix o_prefix;
public __acl_entry_ext i;
}

// typedef struct __acl_ext    *acl_t;
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct __acl_ext
{
// typedef struct acl_entry_obj_tag acl_entry_obj;
// acl_entry_obj      *a_prev, *a_next;
// acl_entry_obj      *a_curr;
// acl_entry_obj      *a_prealloc, *a_prealloc_end;
public acl_entry_obj_tag* a_prev;
public acl_entry_obj_tag* a_next;
public acl_entry_obj_tag* a_curr;
public acl_entry_obj_tag* a_prealloc;
public acl_entry_obj_tag* a_prealloc_end;
// size_t a_used; // typedef __SIZE_TYPE__ size_t;
public ulong a_used;
}

[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct acl_obj_tag
{
public obj_prefix o_prefix;
public __acl_ext i;
}

[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct __acl_entry
{
acl_tag_t e_tag;
// qualifier_obj      e_id; // typedef struct qualifier_obj_tag qualifier_obj;
qualifier_obj_tag e_id;
// acl_permset_obj    e_perm;  //typedef struct acl_permset_obj_tag acl_permset_obj;
acl_permset_obj_tag e_perm;
}

// typedef struct __acl_entry_ext  *acl_entry_t;
[System.Runtime.InteropServices.StructLayout(System.Runtime.InteropServices.LayoutKind.Sequential)]
public unsafe struct __acl_entry_ext
{
// acl_entry_obj      *e_prev, *e_next; // typedef struct acl_entry_obj_tag acl_entry_obj;
public acl_entry_obj_tag* e_prev;
public acl_entry_obj_tag* e_next;
// acl_obj       *e_container; // typedef struct acl_obj_tag acl_obj;
public acl_obj_tag* e_container;
public __acl_entry e_entry;
}