Swift中URL.resolvingSymlinksInPath()解析/sys目录下符号链接行为异常的问题咨询

大家好，我最近在Debian系统上用Swift 5.9写一个控制电脑风扇转速的小玩具应用，遇到了一个让我摸不着头脑的问题，想请教下各位大佬。

我需要读取一个符号链接目录的内容，但知道FileManager.contentsOfDirectory()不会跟随符号链接，所以打算用URL类的.resolvingSymlinksInPath()方法直接解析符号链接的路径。

复现代码 #

import Foundation

let fm = FileManager.default

print(URL(fileURLWithPath: "/sys/class/hwmon/hwmon6").resolvingSymlinksInPath())

符号链接验证 #

我已经确认/sys/class/hwmon/hwmon6是符号链接，执行ls -l /sys/class/hwmon/的输出如下：

byrth@utah ~> ls -l /sys/class/hwmon/                                                   (base)

lrwxrwxrwx - root 10 Dec 16:01 hwmon0 -> ../../devices/LNXSYSTM:00/LNXSYBUS:00/PNP0C0A:00/power_supply/BAT0/hwmon0

lrwxrwxrwx - root 10 Dec 16:01 hwmon1 -> ../../devices/pci0000:00/0000:00:1d.4/0000:03:00.0/nvme/nvme0/hwmon1

lrwxrwxrwx - root 10 Dec 16:01 hwmon2 -> ../../devices/platform/coretemp.0/hwmon/hwmon2

lrwxrwxrwx - root 10 Dec 16:01 hwmon3 -> ../../devices/LNXSYSTM:00/LNXSYBUS:00/ACPI0003:00/power_supply/AC/hwmon3

lrwxrwxrwx - root 10 Dec 16:01 hwmon4 -> ../../devices/virtual/thermal/thermal_zone4/hwmon4

lrwxrwxrwx - root 10 Dec 16:01 hwmon5 -> ../../devices/platform/dell_smm_hwmon/hwmon/hwmon5

lrwxrwxrwx - root 10 Dec 16:01 hwmon6 -> ../../devices/platform/USBC000:00/power_supply/ucsi-source-psy-USBC000:001/hwmon6

lrwxrwxrwx - root 10 Dec 16:01 hwmon7 -> ../../devices/virtual/thermal/thermal_zone6/hwmon7

异常的运行结果 #

但奇怪的是，我运行这个Swift程序后，输出居然还是原路径：

byrth@utah /tmp> swift my-program.swift                                                    (base)

file:///sys/class/hwmon/hwmon6/

byrth@utah /tmp>                                                                           (base)

strace跟踪分析 #

为了搞清楚原因，我用strace跟踪了编译后的程序，发现了一些关键的系统调用信息：

... other strace information ...

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFLNK|0777, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFDIR|0755, st_size=0, ...}, 0) = 0

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFLNK|0777, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFDIR|0755, st_size=0, ...}, 0) = 0

readlink("/sys", 0x56166c31b410, 4097)  = -1 EINVAL (Invalid argument)

readlink("/sys/class", 0x56166c31b410, 4097) = -1 EINVAL (Invalid argument)

readlink("/sys/class/hwmon", 0x56166c31b410, 4097) = -1 EINVAL (Invalid argument)

readlink("/sys/class/hwmon/hwmon6", "../../devices/platform/USBC000:0"..., 4097) = 81

getcwd("/tmp", 1024)                    = 5

readlink("/devices", 0x7ffc5feea050, 1023) = -1 ENOENT (No such file or directory)

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFLNK|0777, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFDIR|0755, st_size=0, ...}, 0) = 0

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFLNK|0777, st_size=0, ...}, AT_SYMLINK_NOFOLLOW) = 0

newfstatat(AT_FDCWD, "/sys/class/hwmon/hwmon6", {st_mode=S_IFDIR|0755, st_size=0, ...}, 0) = 0

newfstatat(1, "", {st_mode=S_IFCHR|0620, st_rdev=makedev(0x88, 0), ...}, AT_EMPTY_PATH) = 0

write(1, "file:///sys/class/hwmon/hwmon6/\n", 32file:///sys/class/hwmon/hwmon6/

) = 32

exit_group(0)                           = ?

从strace的输出能看到，程序明明已经识别出/sys/class/hwmon/hwmon6是符号链接，而且也读取到了它指向的../../devices/platform/USBC000:00/...路径，但之后居然尝试**相对于当前工作目录（/tmp）**去解析这个相对路径，导致找不到/devices目录，最后就返回了原路径。

我想请教各位，这是Swift的resolvingSymlinksInPath()方法的bug吗？还是我对这个方法的理解有误？提前感谢大家的帮助！😉

备注：内容来源于stack exchange，提问作者Beowulf þ e god cyning