内核中不同的大小写文件

Question

克隆当前(094226ad94f4)的内核会在不区分大小写的文件系统上产生这些冲突。

  'include/uapi/linux/netfilter/xt_CONNMARK.h'
  'include/uapi/linux/netfilter/xt_connmark.h'
  'include/uapi/linux/netfilter/xt_DSCP.h'
  'include/uapi/linux/netfilter/xt_dscp.h'
  'include/uapi/linux/netfilter/xt_MARK.h'
  'include/uapi/linux/netfilter/xt_mark.h'
  'include/uapi/linux/netfilter/xt_RATEEST.h'
  'include/uapi/linux/netfilter/xt_rateest.h'
  'include/uapi/linux/netfilter/xt_TCPMSS.h'
  'include/uapi/linux/netfilter/xt_tcpmss.h'
  'include/uapi/linux/netfilter_ipv4/ipt_ECN.h'
  'include/uapi/linux/netfilter_ipv4/ipt_ecn.h'
  'include/uapi/linux/netfilter_ipv4/ipt_TTL.h'
  'include/uapi/linux/netfilter_ipv4/ipt_ttl.h'
  'include/uapi/linux/netfilter_ipv6/ip6t_HL.h'
  'include/uapi/linux/netfilter_ipv6/ip6t_hl.h'
  'net/netfilter/xt_DSCP.c'
  'net/netfilter/xt_dscp.c'
  'net/netfilter/xt_HL.c'
  'net/netfilter/xt_hl.c'
  'net/netfilter/xt_RATEEST.c'
  'net/netfilter/xt_rateest.c'
  'net/netfilter/xt_TCPMSS.c'
  'net/netfilter/xt_tcpmss.c'
  'tools/memory-model/litmus-tests/Z6.0+pooncelock+poonceLock+pombonce.litmus'
  'tools/memory-model/litmus-tests/Z6.0+pooncelock+pooncelock+pombonce.litmus'

有人能向我解释一下，为什么我们每个头文件都有两个拷贝，名字略有不同吗？

Answer 1

所有Linux文件系统都是区分大小写的，因此对于Linux内核源代码来说，不需要区分大小写。

每一种代码都是相似的，但并不相同。

例如，对于类似的概念，这两者是不同的。您可以在内核配置选项之间进行选择。

匹配版本在xt_hl.c中：

IP tables module for matching the value of the TTL
Hop Limit matching module

config NETFILTER_XT_MATCH_HL
tristate '"hl" hoplimit/TTL match support'
depends on NETFILTER_ADVANCED
help
HL matching allows you to match packets based on the hoplimit
in the IPv6 header, or the time-to-live field in the IPv4
header of the packet.

Match允许编写查找给定hoplimit的iptable规则。

目标版本在xt_HL.c中：

TTL modification target for IP tables
Hop Limit modification target for ip6tables

config NETFILTER_XT_TARGET_HL
tristate '"HL" hoplimit target support'
depends on IP_NF_MANGLE || IP6_NF_MANGLE
depends on NETFILTER_ADVANCED
help
This option adds the "HL" (for IPv6) and "TTL" (for IPv4)
targets, which enable the user to change the
hoplimit/time-to-live value of the IP header.

While it is safe to decrement the hoplimit/TTL value, the
modules also allow to increment and set the hoplimit value of
the header to arbitrary values. This is EXTREMELY DANGEROUS
since you can easily create immortal packets that loop
forever on the network.

Target添加支持来编写修改数据包上的hoplimit的iptables规则。

通过处理ip表和hoplimits，代码是相似的。