[RFC, PATCH] netlink based mq_notify(SIGEV_THREAD)
From: Manfred Spraul
Date: Sat Apr 03 2004 - 14:45:56 EST
mq_notify(SIGEV_THREAD) must be implemented in user space. If an event
is triggered, the kernel must send a notification to user space, and
then glibc must create the thread with the requested attributes for the
notification callback. The current implementation in Andrew's -mm tree
uses single shot file descriptor - it works, but it's resource hungry.
Attached is a new proposal:
- split netlink_unicast into separate substeps
- use an AF_NETLINK socket for the message queue notification
What do you think?
--
Manfred
// $Header$
// Kernel Version:
// VERSION = 2
// PATCHLEVEL = 6
// SUBLEVEL = 5
// EXTRAVERSION =-rc3-mm1
--- 2.6/include/linux/netlink.h 2004-04-03 14:29:26.000000000 +0200
+++ build-2.6/include/linux/netlink.h 2004-04-03 21:05:11.525685846 +0200
@@ -120,6 +120,13 @@
extern int netlink_register_notifier(struct notifier_block *nb);
extern int netlink_unregister_notifier(struct notifier_block *nb);
+/* finegrained unicast helpers: */
+struct sock *netlink_getsockbypid(struct sock *ssk, u32 pid);
+struct sock *netlink_getsockbyfilp(struct file *filp);
+int netlink_attachskb(struct sock *sk, struct sk_buff *skb, int nonblock, long timeo);
+void netlink_detachskb(struct sock *sk, struct sk_buff *skb);
+int netlink_sendskb(struct sock *sk, struct sk_buff *skb, int protocol);
+
/*
* skb should fit one page. This choice is good for headerless malloc.
*
--- 2.6/net/netlink/af_netlink.c 2004-03-31 18:36:32.000000000 +0200
+++ build-2.6/net/netlink/af_netlink.c 2004-04-03 21:30:26.147554044 +0200
@@ -415,38 +415,66 @@
}
}
-int netlink_unicast(struct sock *ssk, struct sk_buff *skb, u32 pid, int nonblock)
+struct sock *netlink_getsockbypid(struct sock *ssk, u32 pid)
{
- struct sock *sk;
- struct netlink_opt *nlk;
- int len = skb->len;
int protocol = ssk->sk_protocol;
- long timeo;
- DECLARE_WAITQUEUE(wait, current);
-
- timeo = sock_sndtimeo(ssk, nonblock);
+ struct sock *sock;
+ struct netlink_opt *nlk;
-retry:
- sk = netlink_lookup(protocol, pid);
- if (sk == NULL)
- goto no_dst;
- nlk = nlk_sk(sk);
+ sock = netlink_lookup(protocol, pid);
+ if (!sock)
+ return ERR_PTR(-ECONNREFUSED);
/* Don't bother queuing skb if kernel socket has no input function */
- if (nlk->pid == 0 && !nlk->data_ready)
- goto no_dst;
+ nlk = nlk_sk(sock);
+ if (nlk->pid == 0 && !nlk->data_ready) {
+ sock_put(sock);
+ return ERR_PTR(-ECONNREFUSED);
+ }
+ return sock;
+}
+
+struct sock *netlink_getsockbyfilp(struct file *filp)
+{
+ struct inode *inode = filp->f_dentry->d_inode;
+ struct socket *socket;
+ struct sock *sock;
+
+ if (!inode->i_sock || !(socket = SOCKET_I(inode)))
+ return ERR_PTR(-ENOTSOCK);
+
+ sock = socket->sk;
+ if (sock->sk_family != AF_NETLINK)
+ return ERR_PTR(-EINVAL);
+
+ sock_hold(sock);
+ return sock;
+}
+
+/*
+ * Attach a skb to a netlink socket.
+ * The caller must hold a reference to the destination socket. On error, the
+ * reference is dropped. The skb is not send to the destination, just all
+ * all error checks are performed and memory in the queue is reserved.
+ * Return values:
+ * < 0: error. skb freed, reference to sock dropped.
+ * 0: continue
+ * 1: repeat lookup - reference dropped while waiting for socket memory.
+ */
+int netlink_attachskb(struct sock *sk, struct sk_buff *skb, int nonblock, long timeo)
+{
+ struct netlink_opt *nlk;
+
+ nlk = nlk_sk(sk);
#ifdef NL_EMULATE_DEV
- if (nlk->handler) {
- skb_orphan(skb);
- len = nlk->handler(protocol, skb);
- sock_put(sk);
- return len;
- }
+ if (nlk->handler)
+ return 0;
#endif
if (atomic_read(&sk->sk_rmem_alloc) > sk->sk_rcvbuf ||
test_bit(0, &nlk->state)) {
+ DECLARE_WAITQUEUE(wait, current);
if (!timeo) {
if (!nlk->pid)
netlink_overrun(sk);
@@ -471,19 +499,62 @@
kfree_skb(skb);
return sock_intr_errno(timeo);
}
- goto retry;
+ return 1;
}
-
skb_orphan(skb);
skb_set_owner_r(skb, sk);
+ return 0;
+
+}
+
+int netlink_sendskb(struct sock *sk, struct sk_buff *skb, int protocol)
+{
+ struct netlink_opt *nlk;
+ int len = skb->len;
+
+ nlk = nlk_sk(sk);
+#ifdef NL_EMULATE_DEV
+ if (nlk->handler) {
+ skb_orphan(skb);
+ len = nlk->handler(protocol, skb);
+ sock_put(sk);
+ return len;
+ }
+#endif
+
skb_queue_tail(&sk->sk_receive_queue, skb);
sk->sk_data_ready(sk, len);
sock_put(sk);
return len;
+}
-no_dst:
+void netlink_detachskb(struct sock *sk, struct sk_buff *skb)
+{
kfree_skb(skb);
- return -ECONNREFUSED;
+ sock_put(sk);
+}
+
+int netlink_unicast(struct sock *ssk, struct sk_buff *skb, u32 pid, int nonblock)
+{
+ struct sock *sk;
+ int err;
+ long timeo;
+
+ timeo = sock_sndtimeo(ssk, nonblock);
+
+retry:
+ sk = netlink_getsockbypid(ssk, pid);
+ if (IS_ERR(sk)) {
+ kfree_skb(skb);
+ return PTR_ERR(skb);
+ }
+ err = netlink_attachskb(sk, skb, nonblock, timeo);
+ if (err == 1)
+ goto retry;
+ if (err)
+ return err;
+
+ return netlink_sendskb(sk, skb, ssk->sk_protocol);
}
static __inline__ int netlink_broadcast_deliver(struct sock *sk, struct sk_buff *skb)
--- 2.6/include/linux/mqueue.h 2004-04-03 14:29:26.000000000 +0200
+++ build-2.6/include/linux/mqueue.h 2004-04-03 21:32:34.006794932 +0200
@@ -30,8 +30,24 @@
long __reserved[4]; /* ignored for input, zeroed for output */
};
+/*
+ * SIGEV_THREAD implementation:
+ * SIGEV_THREAD must be implemented in user space. If SIGEV_THREAD is passed
+ * to mq_notify, then
+ * - sigev_signo must be the file descriptor of an AF_NETLINK socket. It's not
+ * necessary that the socket is bound.
+ * - sigev_value.sival_ptr must point to a cookie that is NOTIFY_COOKIE_LEN
+ * bytes long.
+ * If the notification is triggered, then the cookie is sent to the netlink
+ * socket. The first byte of the cookie is replaced with the NOTIFY_?? codes:
+ * NOTIFY_WOKENUP if the notification got triggered, NOTIFY_REMOVED if it was
+ * removed, either due to a close() on the message queue fd or due to a
+ * mq_notify() that removed the notification.
+ */
#define NOTIFY_NONE 0
#define NOTIFY_WOKENUP 1
#define NOTIFY_REMOVED 2
+#define NOTIFY_COOKIE_LEN 32
+
#endif
--- 2.6/ipc/mqueue.c 2004-04-03 14:29:27.000000000 +0200
+++ build-2.6/ipc/mqueue.c 2004-04-03 20:30:07.207197313 +0200
@@ -20,6 +20,9 @@
#include <linux/poll.h>
#include <linux/mqueue.h>
#include <linux/msg.h>
+#include <linux/skbuff.h>
+#include <linux/netlink.h>
+#include <net/sock.h>
#include "util.h"
#define MQUEUE_MAGIC 0x19800202
@@ -33,9 +36,6 @@
#define STATE_PENDING 1
#define STATE_READY 2
-#define NP_NONE ((void*)NOTIFY_NONE)
-#define NP_WOKENUP ((void*)NOTIFY_WOKENUP)
-#define NP_REMOVED ((void*)NOTIFY_REMOVED)
/* used by sysctl */
#define FS_MQUEUE 1
#define CTL_QUEUESMAX 2
@@ -48,6 +48,8 @@
#define HARD_MSGMAX (131072/sizeof(void*))
#define DFLT_MSGSIZEMAX 16384 /* max message size */
+#define NOTIFY_COOKIE_LEN 32
+
struct ext_wait_queue { /* queue of sleeping tasks */
struct task_struct *task;
struct list_head list;
@@ -56,25 +58,26 @@
};
struct mqueue_inode_info {
- struct mq_attr attr;
+ spinlock_t lock;
+ struct inode vfs_inode;
+ wait_queue_head_t wait_q;
+
struct msg_msg **messages;
+ struct mq_attr attr;
- pid_t notify_owner; /* != 0 means notification registered */
- struct sigevent notify;
- struct file *notify_filp;
+ struct sigevent notify; /* notify.sigev_notify == SIGEV_NONE means */
+ pid_t notify_owner; /* no notification registered */
+ struct sock *notify_sock;
+ struct sk_buff *notify_cookie;
/* for tasks waiting for free space and messages, respectively */
struct ext_wait_queue e_wait_q[2];
- wait_queue_head_t wait_q;
unsigned long qsize; /* size of queue in memory (sum of all msgs) */
- spinlock_t lock;
- struct inode vfs_inode;
};
static struct inode_operations mqueue_dir_inode_operations;
static struct file_operations mqueue_file_operations;
-static struct file_operations mqueue_notify_fops;
static struct super_operations mqueue_super_ops;
static void remove_notification(struct mqueue_inode_info *info);
@@ -119,7 +122,7 @@
init_waitqueue_head(&info->wait_q);
INIT_LIST_HEAD(&info->e_wait_q[0].list);
INIT_LIST_HEAD(&info->e_wait_q[1].list);
- info->notify_owner = 0;
+ info->notify.sigev_notify = SIGEV_NONE;
info->qsize = 0;
memset(&info->attr, 0, sizeof(info->attr));
info->attr.mq_maxmsg = DFLT_MSGMAX;
@@ -283,10 +286,11 @@
snprintf(buffer, sizeof(buffer),
"QSIZE:%-10lu NOTIFY:%-5d SIGNO:%-5d NOTIFY_PID:%-6d\n",
info->qsize,
- info->notify_owner ? info->notify.sigev_notify : SIGEV_NONE,
- (info->notify_owner && info->notify.sigev_notify == SIGEV_SIGNAL ) ?
+ info->notify.sigev_notify,
+ (info->notify.sigev_notify == SIGEV_SIGNAL ) ?
info->notify.sigev_signo : 0,
- info->notify_owner);
+ (info->notify.sigev_notify != SIGEV_NONE) ?
+ info->notify_owner : 0);
spin_unlock(&info->lock);
buffer[sizeof(buffer)-1] = '\0';
slen = strlen(buffer)+1;
@@ -299,7 +303,7 @@
count = slen - o;
if (copy_to_user(u_data, buffer + o, count))
- return -EFAULT;
+ return -EFAULT;
*off = o + count;
filp->f_dentry->d_inode->i_atime = filp->f_dentry->d_inode->i_ctime = CURRENT_TIME;
@@ -311,7 +315,8 @@
struct mqueue_inode_info *info = MQUEUE_I(filp->f_dentry->d_inode);
spin_lock(&info->lock);
- if (current->tgid == info->notify_owner)
+ if (info->notify.sigev_notify != SIGEV_NONE &&
+ current->tgid == info->notify_owner)
remove_notification(info);
spin_unlock(&info->lock);
@@ -445,7 +450,8 @@
* waiting synchronously for message AND state of queue changed from
* empty to not empty. Here we are sure that no one is waiting
* synchronously. */
- if (info->notify_owner && info->attr.mq_curmsgs == 1) {
+ if (info->notify.sigev_notify != SIGEV_NONE &&
+ info->attr.mq_curmsgs == 1) {
/* sends signal */
if (info->notify.sigev_notify == SIGEV_SIGNAL) {
struct siginfo sig_i;
@@ -460,10 +466,11 @@
kill_proc_info(info->notify.sigev_signo,
&sig_i, info->notify_owner);
} else if (info->notify.sigev_notify == SIGEV_THREAD) {
- info->notify_filp->private_data = (void*)NP_WOKENUP;
+ *(char*)info->notify_cookie->data = NOTIFY_WOKENUP;
+ netlink_sendskb(info->notify_sock, info->notify_cookie, 0);
}
/* after notification unregisters process */
- info->notify_owner = 0;
+ info->notify.sigev_notify = SIGEV_NONE;
}
wake_up(&info->wait_q);
}
@@ -499,90 +506,13 @@
return timeout;
}
-/*
- * File descriptor based notification, intended to be used to implement
- * SIGEV_THREAD:
- * SIGEV_THREAD means that a notification function should be called in the
- * context of a new thread. The kernel can't do that. Therefore mq_notify
- * calls with SIGEV_THREAD return a new file descriptor. A user space helper
- * must create a new thread and then read from the given file descriptor.
- * The read always returns one byte. If it's NOTIFY_WOKENUP, then it must
- * call the notification function. If it's NOTIFY_REMOVED, then the
- * notification was removed. The file descriptor supports poll, thus one
- * supervisor thread can manage multiple message queue notifications.
- *
- * The implementation must support multiple outstanding notifications:
- * It's possible that a new notification is added and signaled before user
- * space calls mqueue_notify_read for the previous notification.
- * Therefore the notification state is stored in the private_data field of
- * the file descriptor.
- */
-static unsigned int mqueue_notify_poll(struct file *filp,
- struct poll_table_struct *poll_tab)
-{
- struct mqueue_inode_info *info = MQUEUE_I(filp->f_dentry->d_inode);
- int retval;
-
- poll_wait(filp, &info->wait_q, poll_tab);
-
- if (filp->private_data == NP_NONE)
- retval = 0;
- else
- retval = POLLIN | POLLRDNORM;
- return retval;
-}
-
-static ssize_t mqueue_notify_read(struct file *filp, char __user *buf,
- size_t count, loff_t *ppos)
-{
- struct mqueue_inode_info *info = MQUEUE_I(filp->f_dentry->d_inode);
- char result;
-
- if (!count)
- return 0;
- if (*ppos != 0)
- return 0;
- spin_lock(&info->lock);
- while (filp->private_data == NP_NONE) {
- DEFINE_WAIT(wait);
- if (filp->f_flags & O_NONBLOCK) {
- spin_unlock(&info->lock);
- return -EAGAIN;
- }
- prepare_to_wait(&info->wait_q, &wait, TASK_INTERRUPTIBLE);
- spin_unlock(&info->lock);
- schedule();
- finish_wait(&info->wait_q, &wait);
- spin_lock(&info->lock);
- }
- spin_unlock(&info->lock);
- result = (char)(unsigned long)filp->private_data;
- if (put_user(result, buf))
- return -EFAULT;
- *ppos = 1;
- return 1;
-}
-
-static int mqueue_notify_release(struct inode *inode, struct file *filp)
-{
- struct mqueue_inode_info *info = MQUEUE_I(filp->f_dentry->d_inode);
-
- spin_lock(&info->lock);
- if (info->notify_owner && info->notify_filp == filp)
- info->notify_owner = 0;
- filp->private_data = NP_REMOVED;
- spin_unlock(&info->lock);
-
- return 0;
-}
-
static void remove_notification(struct mqueue_inode_info *info)
{
if (info->notify.sigev_notify == SIGEV_THREAD) {
- info->notify_filp->private_data = NP_REMOVED;
- wake_up(&info->wait_q);
+ *(char*)info->notify_cookie->data = NOTIFY_REMOVED;
+ netlink_sendskb(info->notify_sock, info->notify_cookie, 0);
}
- info->notify_owner = 0;
+ info->notify.sigev_notify = SIGEV_NONE;
}
/*
@@ -780,7 +710,8 @@
*/
/* pipelined_send() - send a message directly to the task waiting in
- * sys_mq_timedreceive() (without inserting message into a queue). */
+ * sys_mq_timedreceive() (without inserting message into a queue).
+ */
static inline void pipelined_send(struct mqueue_inode_info *info,
struct msg_msg *message,
struct ext_wait_queue *receiver)
@@ -974,12 +905,16 @@
asmlinkage long sys_mq_notify(mqd_t mqdes,
const struct sigevent __user *u_notification)
{
- int ret, fd;
- struct file *filp, *nfilp;
+ int ret;
+ struct file *filp;
+ struct sock *sock;
struct inode *inode;
struct sigevent notification;
struct mqueue_inode_info *info;
+ struct sk_buff *nc;
+ nc = NULL;
+ sock = NULL;
if (u_notification == NULL) {
notification.sigev_notify = SIGEV_NONE;
} else {
@@ -996,6 +931,44 @@
notification.sigev_signo > _NSIG)) {
return -EINVAL;
}
+ if (notification.sigev_notify == SIGEV_THREAD) {
+ /* create the notify skb */
+ nc = alloc_skb(NOTIFY_COOKIE_LEN, GFP_KERNEL);
+ ret = -ENOMEM;
+ if (!nc)
+ goto out;
+ ret = -EFAULT;
+ if (copy_from_user(nc->data,
+ notification.sigev_value.sival_ptr,
+ NOTIFY_COOKIE_LEN)) {
+ goto out;
+ }
+
+ /* TODO: add a header? */
+ skb_put(nc, NOTIFY_COOKIE_LEN);
+ /* and attach it to the socket */
+retry:
+ filp = fget(notification.sigev_signo);
+ ret = -EBADF;
+ if (!filp)
+ goto out;
+ sock = netlink_getsockbyfilp(filp);
+ fput(filp);
+ if (IS_ERR(sock)) {
+ ret = PTR_ERR(sock);
+ sock = NULL;
+ goto out;
+ }
+
+ ret = netlink_attachskb(sock, nc, 0, MAX_SCHEDULE_TIMEOUT);
+ if (ret == 1)
+ goto retry;
+ if (ret) {
+ sock = NULL;
+ nc = NULL;
+ goto out;
+ }
+ }
}
ret = -EBADF;
@@ -1009,47 +982,33 @@
info = MQUEUE_I(inode);
ret = 0;
- if (notification.sigev_notify == SIGEV_THREAD) {
- ret = get_unused_fd();
- if (ret < 0)
- goto out_fput;
- fd = ret;
- nfilp = get_empty_filp();
- if (!nfilp) {
- ret = -ENFILE;
- goto out_dropfd;
- }
- nfilp->private_data = NP_NONE;
- nfilp->f_op = &mqueue_notify_fops;
- nfilp->f_vfsmnt = mntget(mqueue_mnt);
- nfilp->f_dentry = dget(filp->f_dentry);
- nfilp->f_mapping = filp->f_dentry->d_inode->i_mapping;
- nfilp->f_flags = O_RDONLY;
- nfilp->f_mode = FMODE_READ;
- } else {
- nfilp = NULL;
- fd = -1;
- }
-
spin_lock(&info->lock);
-
- if (notification.sigev_notify == SIGEV_NONE) {
- if (info->notify_owner == current->tgid) {
+ switch (notification.sigev_notify) {
+ case SIGEV_NONE:
+ if (info->notify.sigev_notify != SIGEV_NONE &&
+ info->notify_owner == current->tgid) {
remove_notification(info);
inode->i_atime = inode->i_ctime = CURRENT_TIME;
}
- } else if (info->notify_owner) {
- ret = -EBUSY;
- } else if (notification.sigev_notify == SIGEV_THREAD) {
- info->notify_filp = nfilp;
- fd_install(fd, nfilp);
- ret = fd;
- fd = -1;
- nfilp = NULL;
+ break;
+ case SIGEV_THREAD:
+ if (info->notify.sigev_notify != SIGEV_NONE) {
+ ret = -EBUSY;
+ break;
+ }
+ info->notify_sock = sock;
+ info->notify_cookie = nc;
+ sock = NULL;
+ nc = NULL;
info->notify.sigev_notify = SIGEV_THREAD;
info->notify_owner = current->tgid;
inode->i_atime = inode->i_ctime = CURRENT_TIME;
- } else {
+ break;
+ case SIGEV_SIGNAL:
+ if (info->notify.sigev_notify != SIGEV_NONE) {
+ ret = -EBUSY;
+ break;
+ }
info->notify.sigev_signo = notification.sigev_signo;
info->notify.sigev_value = notification.sigev_value;
info->notify.sigev_notify = SIGEV_SIGNAL;
@@ -1057,12 +1016,14 @@
inode->i_atime = inode->i_ctime = CURRENT_TIME;
}
spin_unlock(&info->lock);
-out_dropfd:
- if (fd != -1)
- put_unused_fd(fd);
out_fput:
fput(filp);
out:
+ if (sock) {
+ netlink_detachskb(sock, nc);
+ } else if (nc) {
+ dev_kfree_skb(nc);
+ }
return ret;
}
@@ -1131,13 +1092,6 @@
.read = mqueue_read_file,
};
-static struct file_operations mqueue_notify_fops = {
- .poll = mqueue_notify_poll,
- .read = mqueue_notify_read,
- .release = mqueue_notify_release,
-};
-
-
static struct super_operations mqueue_super_ops = {
.alloc_inode = mqueue_alloc_inode,
.destroy_inode = mqueue_destroy_inode,