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SubjectRe: [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@profusion.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@profusion.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 &current->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);
> --
> 1.7.5.2
>
>
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