sysctl: replaces some slashes with dots

It turns out that plain sysctl understands a.b/c syntax to write to
/proc/sys/a/b.c. Support this for compatibility.

https://bugs.freedesktop.org/show_bug.cgi?id=77466

2 files changed, 37 insertions, 10 deletions

diff --git a/man/sysctl.d.xml b/man/sysctl.d.xml
index 00a857b11..db53b4959 100644
--- a/man/sysctl.d.xml
+++ b/man/sysctl.d.xml
@@ -68,13 +68,26 @@
                 <para>The configuration files contain a list of
                 variable assignments, separated by newlines. Empty
                 lines and lines whose first non-whitespace character
-                is # or ; are ignored.</para>
-
-                <para>Note that both / and . are accepted as label
-                separators within sysctl variable
-                names. <literal>kernel.domainname=foo</literal> and
-                <literal>kernel/domainname=foo</literal> hence are
-                entirely equivalent.</para>
+                is <literal>#</literal> or <literal>;</literal> are
+                ignored.</para>
+
+                <para>Note that either <literal>/</literal> or
+                <literal>.</literal> may be used as separators within
+                sysctl variable names. If the first separator is a
+                slash, remaining slashes and dots are left intact. If
+                the first separator is a dot, dots and slashes are
+                interchanged. <literal>kernel.domainname=foo</literal>
+                and <literal>kernel/domainname=foo</literal> are
+                equivalent and will cause <literal>foo</literal> to
+                be written to
+                <filename>/proc/sys/kernel/domainname</filename>.
+                Either
+                <literal>net.ipv4.conf.enp3s0/200.forwarding</literal>
+                or
+                <literal>net/ipv4/conf/enp3s0.200/forwarding</literal>
+                may be used to refer to
+                <filename>/proc/sys/net/ipv4/conf/enp3s0.200/forwarding</filename>.
+                </para>
 
                 <para>Each configuration file shall be named in the
                 style of <filename><replaceable>program</replaceable>.conf</filename>.
@@ -109,7 +122,7 @@
                 early on boot. The network interface-specific options
                 will also be applied individually for each network
                 interface as it shows up in the system. (More
-                specifically, that is
+                specifically,
                 <filename>net.ipv4.conf.*</filename>,
                 <filename>net.ipv6.conf.*</filename>,
                 <filename>net.ipv4.neigh.*</filename> and <filename>net.ipv6.neigh.*</filename>)</para>
diff --git a/src/sysctl/sysctl.c b/src/sysctl/sysctl.c
index 283eefe1a..06defa5b7 100644
--- a/src/sysctl/sysctl.c
+++ b/src/sysctl/sysctl.c
@@ -48,12 +48,26 @@ static const char conf_file_dirs[] =
 #endif
         ;
 
-static char *normalize_sysctl(char *s) {
+static char* normalize_sysctl(char *s) {
         char *n;
 
-        for (n = s; *n; n++)
+        n = strpbrk(s, "/.");
+        /* If the first separator is a slash, the path is
+         * assumed to be normalized and slashes remain slashes
+         * and dots remains dots. */
+        if (!n || *n == '/')
+                return s;
+
+        /* Otherwise, dots become slashes and slashes become
+         * dots. Fun. */
+        while (n) {
                 if (*n == '.')
                         *n = '/';
+                else
+                        *n = '.';
+
+                n = strpbrk(n + 1, "/.");
+        }
 
         return s;
 }