Commit f1ecf068 authored by Lucas De Marchi's avatar Lucas De Marchi Committed by Linus Torvalds
Browse files

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: default avatarLucas 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: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 088024b1

fs/proc/proc_sysctl.c

+45 −0
Original line number Diff line number Diff line
@@ -3,6 +3,7 @@ 
 */

#include <linux/init.h>

#include <linux/sysctl.h>

#include <linux/poll.h>

#include <linux/proc_fs.h>

#include <linux/security.h>

#include <linux/namei.h>
@@ -14,6 +15,15 @@ static const struct inode_operations proc_sys_inode_operations; 
static const struct file_operations proc_sys_dir_file_operations;

static const struct inode_operations proc_sys_dir_operations;



void proc_sys_poll_notify(struct ctl_table_poll *poll)

{

	if (!poll)

		return;



	atomic_inc(&poll->event);

	wake_up_interruptible(&poll->wait);

}



static struct inode *proc_sys_make_inode(struct super_block *sb,

		struct ctl_table_header *head, struct ctl_table *table)

{
@@ -176,6 +186,39 @@ static ssize_t proc_sys_write(struct file *filp, const char __user *buf, 
	return proc_sys_call_handler(filp, (void __user *)buf, count, ppos, 1);

}



static int proc_sys_open(struct inode *inode, struct file *filp)

{

	struct ctl_table *table = PROC_I(inode)->sysctl_entry;



	if (table->poll)

		filp->private_data = proc_sys_poll_event(table->poll);



	return 0;

}



static unsigned int proc_sys_poll(struct file *filp, poll_table *wait)

{

	struct inode *inode = filp->f_path.dentry->d_inode;

	struct ctl_table *table = PROC_I(inode)->sysctl_entry;

	unsigned long event = (unsigned long)filp->private_data;

	unsigned int ret = DEFAULT_POLLMASK;



	if (!table->proc_handler)

		goto out;



	if (!table->poll)

		goto out;



	poll_wait(filp, &table->poll->wait, wait);



	if (event != atomic_read(&table->poll->event)) {

		filp->private_data = proc_sys_poll_event(table->poll);

		ret = POLLIN | POLLRDNORM | POLLERR | POLLPRI;

	}



out:

	return ret;

}



static int proc_sys_fill_cache(struct file *filp, void *dirent,

				filldir_t filldir,
@@ -364,6 +407,8 @@ static int proc_sys_getattr(struct vfsmount *mnt, struct dentry *dentry, struct 
}



static const struct file_operations proc_sys_file_operations = {

	.open		= proc_sys_open,

	.poll		= proc_sys_poll,

	.read		= proc_sys_read,

	.write		= proc_sys_write,

	.llseek		= default_llseek,

include/linux/sysctl.h

+22 −0
Original line number Diff line number Diff line
@@ -931,6 +931,7 @@ enum 
#ifdef __KERNEL__

#include <linux/list.h>

#include <linux/rcupdate.h>

#include <linux/wait.h>



/* For the /proc/sys support */

struct ctl_table;
@@ -1011,6 +1012,26 @@ extern int proc_do_large_bitmap(struct ctl_table *, int, 
 * cover common cases.

 */



/* Support for userspace poll() to watch for changes */

struct ctl_table_poll {

	atomic_t event;

	wait_queue_head_t wait;

};



static inline void *proc_sys_poll_event(struct ctl_table_poll *poll)

{

	return (void *)(unsigned long)atomic_read(&poll->event);

}



void proc_sys_poll_notify(struct ctl_table_poll *poll);



#define __CTL_TABLE_POLL_INITIALIZER(name) {				\

	.event = ATOMIC_INIT(0),					\

	.wait = __WAIT_QUEUE_HEAD_INITIALIZER(name.wait) }



#define DEFINE_CTL_TABLE_POLL(name)					\

	struct ctl_table_poll name = __CTL_TABLE_POLL_INITIALIZER(name)



/* A sysctl table is an array of struct ctl_table: */

struct ctl_table 

{
@@ -1021,6 +1042,7 @@ struct ctl_table 
	struct ctl_table *child;

	struct ctl_table *parent;	/* Automatically set */

	proc_handler *proc_handler;	/* Callback for text formatting */

	struct ctl_table_poll *poll;

	void *extra1;

	void *extra2;

};

include/linux/utsname.h

+16 −0
Original line number Diff line number Diff line
@@ -37,6 +37,14 @@ struct new_utsname { 
#include <linux/nsproxy.h>

#include <linux/err.h>



enum uts_proc {

	UTS_PROC_OSTYPE,

	UTS_PROC_OSRELEASE,

	UTS_PROC_VERSION,

	UTS_PROC_HOSTNAME,

	UTS_PROC_DOMAINNAME,

};



struct user_namespace;

extern struct user_namespace init_user_ns;
@@ -80,6 +88,14 @@ static inline struct uts_namespace *copy_utsname(unsigned long flags, 
}

#endif



#ifdef CONFIG_PROC_SYSCTL

extern void uts_proc_notify(enum uts_proc proc);

#else

static inline void uts_proc_notify(enum uts_proc proc)

{

}

#endif



static inline struct new_utsname *utsname(void)

{

	return &current->nsproxy->uts_ns->name;

kernel/sys.c

+2 −0
Original line number Diff line number Diff line
@@ -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;

}

kernel/utsname_sysctl.c

+23 −0
Original line number Diff line number Diff line
@@ -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);

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