sysctl: add support for poll()

Adding support for poll() in sysctl fs allows userspace to receive
notifications of changes in sysctl entries.  This adds a infrastructure to
allow files in sysctl fs to be pollable and implements it for hostname and
domainname.

[akpm@linux-foundation.org: s/declare/define/ for definitions]
Signed-off-by: Lucas De Marchi <lucas.demarchi@profusion.mobi>
Cc: Greg KH <gregkh@suse.de>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

2 files changed, 25 insertions, 0 deletions

diff --git a/kernel/sys.c b/kernel/sys.c
index 58459509b14c..d06c091e0345 100644
--- a/kernel/sys.c
+++ b/kernel/sys.c
@@ -1286,6 +1286,7 @@ SYSCALL_DEFINE2(sethostname, char __user *, name, int, len)
                 memset(u->nodename + len, 0, sizeof(u->nodename) - len);
                 errno = 0;
         }
+        uts_proc_notify(UTS_PROC_HOSTNAME);
         up_write(&uts_sem);
         return errno;
 }
@@ -1336,6 +1337,7 @@ SYSCALL_DEFINE2(setdomainname, char __user *, name, int, len)
                 memset(u->domainname + len, 0, sizeof(u->domainname) - len);
                 errno = 0;
         }
+        uts_proc_notify(UTS_PROC_DOMAINNAME);
         up_write(&uts_sem);
         return errno;
 }
diff --git a/kernel/utsname_sysctl.c b/kernel/utsname_sysctl.c
index a2cd77e70d4d..3b0d48ebf81d 100644
--- a/kernel/utsname_sysctl.c
+++ b/kernel/utsname_sysctl.c
@@ -13,6 +13,7 @@
 #include <linux/uts.h>
 #include <linux/utsname.h>
 #include <linux/sysctl.h>
+#include <linux/wait.h>
 
 static void *get_uts(ctl_table *table, int write)
 {
@@ -51,12 +52,19 @@ static int proc_do_uts_string(ctl_table *table, int write,
         uts_table.data = get_uts(table, write);
         r = proc_dostring(&uts_table,write,buffer,lenp, ppos);
         put_uts(table, write, uts_table.data);
+
+        if (write)
+                proc_sys_poll_notify(table->poll);
+
         return r;
 }
 #else
 #define proc_do_uts_string NULL
 #endif
 
+static DEFINE_CTL_TABLE_POLL(hostname_poll);
+static DEFINE_CTL_TABLE_POLL(domainname_poll);
+
 static struct ctl_table uts_kern_table[] = {
         {
                 .procname       = "ostype",
@@ -85,6 +93,7 @@ static struct ctl_table uts_kern_table[] = {
                 .maxlen         = sizeof(init_uts_ns.name.nodename),
                 .mode           = 0644,
                 .proc_handler   = proc_do_uts_string,
+                .poll           = &hostname_poll,
         },
         {
                 .procname       = "domainname",
@@ -92,6 +101,7 @@ static struct ctl_table uts_kern_table[] = {
                 .maxlen         = sizeof(init_uts_ns.name.domainname),
                 .mode           = 0644,
                 .proc_handler   = proc_do_uts_string,
+                .poll           = &domainname_poll,
         },
         {}
 };
@@ -105,6 +115,19 @@ static struct ctl_table uts_root_table[] = {
         {}
 };
 
+#ifdef CONFIG_PROC_SYSCTL
+/*
+ * Notify userspace about a change in a certain entry of uts_kern_table,
+ * identified by the parameter proc.
+ */
+void uts_proc_notify(enum uts_proc proc)
+{
+        struct ctl_table *table = &uts_kern_table[proc];
+
+        proc_sys_poll_notify(table->poll);
+}
+#endif
+
 static int __init utsname_sysctl_init(void)
 {
         register_sysctl_table(uts_root_table);