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Date: Wed, 1 Jun 2011 23:51:37 -0300 From: Lucas De Marchi <lucas.demarchi@...fusion.mobi> To: linux-kernel@...r.kernel.org Cc: kay.sievers@...y.org, Lucas De Marchi <lucas.demarchi@...fusion.mobi>, Nick Piggin <npiggin@...nel.dk>, Al Viro <viro@...iv.linux.org.uk>, Christoph Hellwig <hch@....de>, "Eric W. Biederman" <ebiederm@...ssion.com>, Stephen Rothwell <sfr@...b.auug.org.au>, Andrew Morton <akpm@...ux-foundation.org>, David Howells <dhowells@...hat.com>, "Serge E. Hallyn" <serge.hallyn@...onical.com>, Daniel Lezcano <daniel.lezcano@...e.fr>, Jiri Slaby <jslaby@...e.cz>, Greg Kroah-Hartman <gregkh@...e.de>, James Morris <jmorris@...ei.org> Subject: Re: [PATCH] sysctl: add support for poll() CC'ing people as suggested by get_maintainer.pl On Wed, Jun 1, 2011 at 9:14 AM, Lucas De Marchi <lucas.demarchi@...fusion.mobi> wrote: > Adding support for poll() in sysctl fs allows userspace to receive > notifications when an entry in sysctl changes. This way it's possible to > know when hostname/domainname is changed due to the respective syscall > has been called or its file under /proc/sys has been written to. > > Signed-off-by: Lucas De Marchi <lucas.demarchi@...fusion.mobi> > --- > fs/proc/proc_sysctl.c | 40 ++++++++++++++++++++++++++++++++++++++++ > include/linux/sysctl.h | 8 ++++++++ > include/linux/utsname.h | 16 ++++++++++++++++ > kernel/sys.c | 2 ++ > kernel/utsname_sysctl.c | 36 ++++++++++++++++++++++++++++++++++++ > 5 files changed, 102 insertions(+), 0 deletions(-) > > diff --git a/fs/proc/proc_sysctl.c b/fs/proc/proc_sysctl.c > index f50133c..2e5d3ec 100644 > --- a/fs/proc/proc_sysctl.c > +++ b/fs/proc/proc_sysctl.c > @@ -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> > @@ -176,6 +177,43 @@ 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) { > + unsigned long event = atomic_read(&table->poll->event); > + > + filp->private_data = (void *)event; > + } > + > + 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 = POLLIN | POLLRDNORM; > + > + 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 = (void *)(unsigned long)atomic_read( > + &table->poll->event); > + ret = POLLIN | POLLRDNORM | POLLERR | POLLPRI; > + } > + > +out: > + return ret; > +} > > static int proc_sys_fill_cache(struct file *filp, void *dirent, > filldir_t filldir, > @@ -367,6 +405,8 @@ 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, > diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h > index 11684d9..96c89ba 100644 > --- a/include/linux/sysctl.h > +++ b/include/linux/sysctl.h > @@ -25,6 +25,7 @@ > #include <linux/kernel.h> > #include <linux/types.h> > #include <linux/compiler.h> > +#include <linux/wait.h> > > struct completion; > > @@ -1011,6 +1012,12 @@ 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; > +}; > + > /* A sysctl table is an array of struct ctl_table: */ > struct ctl_table > { > @@ -1021,6 +1028,7 @@ 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; > }; > diff --git a/include/linux/utsname.h b/include/linux/utsname.h > index 4e5b021..c714ed7 100644 > --- a/include/linux/utsname.h > +++ b/include/linux/utsname.h > @@ -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 ¤t->nsproxy->uts_ns->name; > diff --git a/kernel/sys.c b/kernel/sys.c > index e4128b2..ada9cd7 100644 > --- a/kernel/sys.c > +++ b/kernel/sys.c > @@ -1211,6 +1211,7 @@ 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; > } > @@ -1261,6 +1262,7 @@ 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 a2cd77e..e96b766 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 +52,28 @@ 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) { > + atomic_inc(&table->poll->event); > + wake_up_interruptible(&table->poll->wait); > + } > + > return r; > } > #else > #define proc_do_uts_string NULL > #endif > > +static struct ctl_table_poll hostname_poll = { > + .event = ATOMIC_INIT(0), > + .wait = __WAIT_QUEUE_HEAD_INITIALIZER(hostname_poll.wait), > +}; > + > +static struct ctl_table_poll domainname_poll = { > + .event = ATOMIC_INIT(0), > + .wait = __WAIT_QUEUE_HEAD_INITIALIZER(domainname_poll.wait), > +}; > + > static struct ctl_table uts_kern_table[] = { > { > .procname = "ostype", > @@ -85,6 +102,7 @@ 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 +110,7 @@ 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 +124,23 @@ 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]; > + > + if (!table->poll) > + return; > + > + atomic_inc(&table->poll->event); > + wake_up_interruptible(&table->poll->wait); > +} > +#endif > + > static int __init utsname_sysctl_init(void) > { > register_sysctl_table(uts_root_table); 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