如何从 C# 中的 libc p/invoke getpwnam()？

Question

让我们从文档开始： https://man7.org/linux/man-pages/man3/getpwnam.3.html

有了这个，我编写了以下 C# 代码：

using System;
using System.Runtime.InteropServices;

if (args.Length < 1) {
    Console.Error.WriteLine("Provide user name.");
    Environment.Exit(-1);
}

var name = args[0];

if (RuntimeInformation.IsOSPlatform(OSPlatform.Linux)) {
    Syscall.getpwnam(name, out var passwd);
    Console.WriteLine($"User = {name}, UID = {passwd.Uid}, GID = {passwd.Gid}");
    passwd = GetPasswd(name);
    Console.WriteLine($"User = {name}, UID = {passwd.Uid}, GID = {passwd.Gid}");
}
else {
    Console.WriteLine("It supposed to be run on Linux.");
}

static Passwd GetPasswd(string name) {
    var bufsize = 16384;
    var buf = new byte[bufsize];
    var passwd = new Passwd();
    Syscall.getpwnam_r(name, passwd, buf, (uint)bufsize, out var result);
    return result;
}

public struct Passwd {
    public string Name;
    public string Password;
    public uint Uid;
    public uint Gid;
    public string Gecos;
    public string Directory;
    public string Shell;
}

static class Syscall {

    [DllImport("libc", SetLastError = true)]
    public static extern void getpwnam(string name, out Passwd passwd);

    [DllImport("libc", SetLastError = true)]
    public static extern void getpwnam_r(string name, Passwd passwd, byte[] buf, uint bufsize, out Passwd result);

}

没用。

这是我得到的：

User = service, UID = 0, GID = 0
Segmentation fault (core dumped)

我做错了什么？

我应该如何调用它才能得到实际的结构？我对返回的字符串不感兴趣。我只关心 Uid 和 Gid 值。

Answer 1

如链接文档所述 - 此函数接受一个参数 - 名称和 returns 指向包含数据的结构的指针。所以签名应该是：

[DllImport("libc", SetLastError = true)]
public static extern IntPtr getpwnam(string name);

然后：

// we have pointer here
var passwdPtr = Syscall.getpwnam(name);
// don't forget to check if pointer is not IntPtr.Zero.
// interpret data at pointer as structure
var passwd = Marshal.PtrToStructure<Passwd>(passwdPtr);
Console.WriteLine($"User = {passwd.Name}, UID = {passwd.Uid}, GID = {passwd.Gid}");

如何从 C# 中的 libc p/invoke getpwnam()？

How to p/invoke getpwnam() from libc in C#?

.net

c#

linux

pinvoke