使用 fakeroot/fakechroot 的 ARM Linux rootfs 网络无法正常工作答案

【问题标题】：Network not functioning on an ARM Linux rootfs with fakeroot/fakechroot使用 fakeroot/fakechroot 的 ARM Linux rootfs 网络无法正常工作
【发布时间】：2013-04-23 21:27:56
【问题描述】：

我使用 buildroot 创建了一个 rootfs，但使用了一个带有 glibc 的 crosstool-ng 工具链。这向我展示了所需的最少文件集。然后，我将所有库替换为直接从 armel 的压缩 .deb 包中提取的库。然后我将fakeroot 和fakechroot 添加到组合中（也来自.deb 包）。我还根据自己的喜好修改了resolv.conf、hosts 和nsswitch.conf 文件。将其上传到我的设备后，很多工作都在进行。 cd / 带我到正确的地方。 whoami 返回根目录。但是，任何与 DNS 相关的东西都不起作用。例如ping google.com 返回错误地址。我已经复制了 libnss_* 和 libresolv 库以及我认为必要的所有其他内容。输入相同的设置，但在我的主机上使用 qemu 和 chroot 有效，但我试图找出它在我的目标设备上不起作用的原因。

当我运行 strace ping google.com 时，我得到以下信息：

open("/data/local/target/bin/ping", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\2\0(\0\1\0\0\0\0\314\0\0004\0\0\0"..., 4094) = 4094
close(3)                                = 0
execve("/data/local/target/bin/ping", ["ping", "google.com"], [/* 20 vars */]) = 0
brk(0)                                  = 0xb5000
uname({sys="Linux", node="localhost", ...}) = 0
access("/etc/ld.so.nohwcap", F_OK)      = -1 ENOENT (No such file or directory)
mmap2(NULL, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4001d000
open("/data/local/target/usr/lib/fakechroot/libfakechroot.so", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\364\32\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0666, st_size=45540, ...}) = 0
mmap2(NULL, 77628, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40026000
mprotect(0x40031000, 28672, PROT_NONE)  = 0
mmap2(0x40038000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0xa) = 0x40038000
close(3)                                = 0
open("/data/local/target/usr/lib/libfakeroot/libfakeroot-sysv.so", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\340'\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0666, st_size=29092, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x4001f000
mmap2(NULL, 60672, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40039000
mprotect(0x40040000, 28672, PROT_NONE)  = 0
mmap2(0x40047000, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x6) = 0x40047000
close(3)                                = 0
access("/etc/ld.so.preload", R_OK)      = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libc.so.6", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libc.so.6", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\374V\1\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=1209660, ...}) = 0
mmap2(NULL, 1246468, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40048000
mprotect(0x4016b000, 32768, PROT_NONE)  = 0
mmap2(0x40173000, 12288, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x123) = 0x40173000
mmap2(0x40176000, 9476, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x40176000
close(3)                                = 0
open("tls/v7l/neon/vfp/libdl.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libdl.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0$\t\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=9808, ...}) = 0
mmap2(NULL, 41136, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40179000
mprotect(0x4017b000, 28672, PROT_NONE)  = 0
mmap2(0x40182000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x1) = 0x40182000
close(3)                                = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40020000
set_tls(0x40020170, 0x40020847, 0x40020848, 0x40020170, 0x40025000) = 0
mprotect(0x40182000, 4096, PROT_READ)   = 0
mprotect(0x40173000, 8192, PROT_READ)   = 0
mprotect(0xb1000, 4096, PROT_READ)      = 0
mprotect(0x40024000, 4096, PROT_READ)   = 0
brk(0)                                  = 0xb5000
brk(0xd6000)                            = 0xd6000
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
open("/etc/nsswitch.conf", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libnss_compat.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnss_compat.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0|\r\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=26480, ...}) = 0
mmap2(NULL, 57952, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40184000
mprotect(0x4018a000, 28672, PROT_NONE)  = 0
mmap2(0x40191000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x5) = 0x40191000
close(3)                                = 0
open("tls/v7l/neon/vfp/libnsl.so.1", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnsl.so.1", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0x/\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=75732, ...}) = 0
mmap2(NULL, 116488, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x40193000
mprotect(0x401a5000, 28672, PROT_NONE)  = 0
mmap2(0x401ac000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x11) = 0x401ac000
mmap2(0x401ae000, 5896, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x401ae000
close(3)                                = 0
mprotect(0x401ac000, 4096, PROT_READ)   = 0
mprotect(0x40191000, 4096, PROT_READ)   = 0
open("/etc/nsswitch.conf", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libnss_nis.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/usr/lib/libnss_nis.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
open("/data/local/target/lib/libnss_nis.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0X\30\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=38608, ...}) = 0
mmap2(NULL, 70236, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401b0000
mprotect(0x401b9000, 28672, PROT_NONE)  = 0
mmap2(0x401c0000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x8) = 0x401c0000
close(3)                                = 0
open("tls/v7l/neon/vfp/libnss_files.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnss_files.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0\330\31\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=42688, ...}) = 0
mmap2(NULL, 74492, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401c2000
mprotect(0x401cc000, 28672, PROT_NONE)  = 0
mmap2(0x401d3000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x9) = 0x401d3000
close(3)                                = 0
mprotect(0x401d3000, 4096, PROT_READ)   = 0
mprotect(0x401c0000, 4096, PROT_READ)   = 0
open("/data/local/target/etc/passwd", O_RDONLY|O_CLOEXEC) = 3
fcntl64(3, F_GETFD)                     = 0x1 (flags FD_CLOEXEC)
_llseek(3, 0, [0], SEEK_CUR)            = 0
fstat64(3, {st_mode=S_IFREG|0666, st_size=596, ...}) = 0
mmap2(NULL, 596, PROT_READ, MAP_SHARED, 3, 0) = 0x40021000
_llseek(3, 596, [596], SEEK_SET)        = 0
munmap(0x40021000, 596)                 = 0
close(3)                                = 0
getpid()                                = 9034
socket(PF_NETLINK, SOCK_RAW, 0)         = 3
bind(3, {sa_family=AF_NETLINK, pid=0, groups=00000000}, 12) = 0
getsockname(3, {sa_family=AF_NETLINK, pid=9034, groups=00000000}, [12]) = 0
gettimeofday({1366748508, 414909}, NULL) = 0
sendto(3, "\24\0\0\0\26\0\1\3\\\355vQ\0\0\0\0\0\0\0\0", 20, 0, {sa_family=AF_NETLINK,     pid=0, groups=00000000}, 12) = 20
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"0\0\0\0\24\0\2\0\\\355vQJ#\0\0\2\10\200\376\1\0\0\0\10\0\1\0\177\0\0\1"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 108
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"@\0\0\0\24\0\2\0\\\355vQJ#\0\0\n\200\200\376\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 128
recvmsg(3, {msg_name(12)={sa_family=AF_NETLINK, pid=0, groups=00000000}, msg_iov(1)=[{"\24\0\0\0\3\0\2\0\\\355vQJ#\0\0\0\0\0\0\1\0\0\0\24\0\1\0\0\0\0\0"..., 4096}], msg_controllen=0, msg_flags=0}, 0) = 20
close(3)                                = 0
open("/etc/resolv.conf", O_RDONLY)      = -1 ENOENT (No such file or directory)
uname({sys="Linux", node="localhost", ...}) = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
socket(PF_FILE, SOCK_STREAM|SOCK_CLOEXEC|SOCK_NONBLOCK, 0) = 3
connect(3, {sa_family=AF_FILE, path="/var/run/nscd/socket"}, 110) = -1 ENOENT (No such file or directory)
close(3)                                = 0
open("/etc/nsswitch.conf", O_RDONLY)    = -1 ENOENT (No such file or directory)
open("tls/v7l/neon/vfp/libnss_dns.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libnss_dns.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0000\v\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=18040, ...}) = 0
mmap2(NULL, 49316, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401d5000
mprotect(0x401d9000, 28672, PROT_NONE)  = 0
mmap2(0x401e0000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x3) = 0x401e0000
close(3)                                = 0
open("tls/v7l/neon/vfp/libresolv.so.2", O_RDONLY) = -1 ENOENT (No such file or directory)
...
open("/data/local/target/lib/libresolv.so.2", O_RDONLY) = 3
read(3, "\177ELF\1\1\1\0\0\0\0\0\0\0\0\0\3\0(\0\1\0\0\0H$\0\0004\0\0\0"..., 512) = 512
fstat64(3, {st_mode=S_IFREG|0777, st_size=71524, ...}) = 0
mmap2(NULL, 79772, PROT_READ|PROT_EXEC, MAP_PRIVATE|MAP_DENYWRITE, 3, 0) = 0x401e2000
mmap2(0x401f2000, 8192, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_DENYWRITE, 3, 0x10) = 0x401f2000
mmap2(0x401f4000, 6044, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_FIXED|MAP_ANONYMOUS, -1, 0) = 0x401f4000
close(3)                                = 0
mprotect(0x401f2000, 4096, PROT_READ)   = 0
mprotect(0x401e0000, 4096, PROT_READ)   = 0
open("/etc/host.conf", O_RDONLY)        = -1 ENOENT (No such file or directory)
stat64("/etc/resolv.conf", 0xbed0eee8)  = -1 ENOENT (No such file or directory)
gettimeofday({1366748508, 437074}, NULL) = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 438028}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\234\32\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 440124}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\234\32\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
gettimeofday({1366748508, 441638}, NULL) = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 442345}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\302\373\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
socket(PF_INET, SOCK_DGRAM|SOCK_NONBLOCK, IPPROTO_IP) = 3
connect(3, {sa_family=AF_INET, sin_port=htons(53), sin_addr=inet_addr("127.0.0.1")}, 16) = 0
gettimeofday({1366748508, 444280}, NULL) = 0
poll([{fd=3, events=POLLOUT}], 1, 0)    = 1 ([{fd=3, revents=POLLOUT}])
send(3, "\302\373\1\0\0\1\0\0\0\0\0\0\6google\3com\0\0\1\0\1", 28, MSG_NOSIGNAL) = 28
poll([{fd=3, events=POLLIN}], 1, 5000)  = 1 ([{fd=3, revents=POLLERR}])
close(3)                                = 0
open("/data/local/target/etc/hosts", O_RDONLY|O_CLOEXEC) = 3
fcntl64(3, F_GETFD)                     = 0x1 (flags FD_CLOEXEC)
fstat64(3, {st_mode=S_IFREG|0666, st_size=40, ...}) = 0
mmap2(NULL, 4096, PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0) = 0x40021000
read(3, "127.0.0.1\tlocalhost\n127.0.1.1\tbu"..., 4096) = 40
read(3, "", 4096)                       = 0
close(3)                                = 0
munmap(0x40021000, 4096)                = 0
write(2, "ping: bad address 'google.com'\n", 31) = 31
exit_group(1)                           = ?

很多事情进展顺利。它知道在搜索可执行文件和库时将 /data/local/target 添加到路径中。你可以看到它找到了各种 libnss_* 库，它发现主机文件不只是在/etc/hosts，但是为什么你认为它没有在正确的位置找到@ 987654333@ 和 resolv.conf?这似乎是一个fakechroot 问题或我如何使用它的问题。

【问题讨论】：

试试ping 8.8.8.8;那样有用吗？它确实尝试了/etc/resolv.conf。此外，/etc/host.conf 表示您是否可以使用解析器。你需要那个。您是说这些文件应该在 /data/local/... 中还是希望搜索 /etc/？此外，如果您再次构建编译器，您可能会喜欢 eglibc。
好问题，我应该包括的东西，因为我已经尝试过了。 ping 8.8.8.8 工作正常，或其他 IP 地址工作正常。我认为它应该尝试查看 /data/local/target/etc 而不是 /etc。出于某种原因，它试图找到 /data/local/target/hosts 和其他一些东西，但不是与此相关的某些关键文件。
是的，uClibc 和 eglibc 处理这个问题的方式不同，但我真的希望 debian 包能够很好地安装，甚至最终运行 debootstrap，它也会创建基于 glibc 的东西并且会遇到同样的问题（我已经尝试过并且大多数工作，但不是 DNS）。
抱歉，对 eglibc 有误解。是的，实际上，我已经在使用它（如前所述，直接从 debian 包中提取）。我在考虑不依赖于 libnss* 文件的 uClibc 和 musl C 库。我以为这就是你的意思。
看起来在其他库/可执行文件中使用 fopen 可以通过使用指向 libfakechroot 的 LD_PRELOAD 来拦截，但不能从 eglibc 本身调用 fopen。我想我将不得不手动编辑 eglibc 源并构建它。看起来他们做得很好，让这一切变得简单。

标签： arm chroot buildroot crosstool-ng

【解决方案1】：

看起来在其他库/可执行文件中使用 fopen 可以通过使用指向 libfakechroot 的 LD_PRELOAD 来拦截，但不能从 eglibc 本身调用 fopen。您将不得不手动编辑 eglibc 源并构建它。看起来他们做得很好，让这一切变得简单。

这已经过测试并且有效。

【讨论】：