1 files changed, 76 insertions, 0 deletions

diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index f1cb1ddde511..cf3786625bfa 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -6,6 +6,7 @@
 #include <linux/fsnotify.h>
 #include <linux/kobject.h>
 #include <linux/namei.h>
+#include <linux/poll.h>
 #include <asm/uaccess.h>
 #include <asm/semaphore.h>
 
@@ -57,6 +58,7 @@ struct sysfs_buffer {
         struct sysfs_ops        * ops;
         struct semaphore        sem;
         int                     needs_read_fill;
+        int                     event;
 };
 
 
@@ -72,6 +74,7 @@ struct sysfs_buffer {
  */
 static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer)
 {
+        struct sysfs_dirent * sd = dentry->d_fsdata;
         struct attribute * attr = to_attr(dentry);
         struct kobject * kobj = to_kobj(dentry->d_parent);
         struct sysfs_ops * ops = buffer->ops;
@@ -83,6 +86,7 @@ static int fill_read_buffer(struct dentry * dentry, struct sysfs_buffer * buffer
         if (!buffer->page)
                 return -ENOMEM;
 
+        buffer->event = atomic_read(&sd->s_event);
         count = ops->show(kobj,attr,buffer->page);
         buffer->needs_read_fill = 0;
         BUG_ON(count > (ssize_t)PAGE_SIZE);
@@ -348,12 +352,84 @@ static int sysfs_release(struct inode * inode, struct file * filp)
         return 0;
 }
 
+/* Sysfs attribute files are pollable.  The idea is that you read
+ * the content and then you use 'poll' or 'select' to wait for
+ * the content to change.  When the content changes (assuming the
+ * manager for the kobject supports notification), poll will
+ * return POLLERR|POLLPRI, and select will return the fd whether
+ * it is waiting for read, write, or exceptions.
+ * Once poll/select indicates that the value has changed, you
+ * need to close and re-open the file, as simply seeking and reading
+ * again will not get new data, or reset the state of 'poll'.
+ * Reminder: this only works for attributes which actively support
+ * it, and it is not possible to test an attribute from userspace
+ * to see if it supports poll (Nether 'poll' or 'select' return
+ * an appropriate error code).  When in doubt, set a suitable timeout value.
+ */
+static unsigned int sysfs_poll(struct file *filp, poll_table *wait)
+{
+        struct sysfs_buffer * buffer = filp->private_data;
+        struct kobject * kobj = to_kobj(filp->f_dentry->d_parent);
+        struct sysfs_dirent * sd = filp->f_dentry->d_fsdata;
+        int res = 0;
+
+        poll_wait(filp, &kobj->poll, wait);
+
+        if (buffer->event != atomic_read(&sd->s_event)) {
+                res = POLLERR|POLLPRI;
+                buffer->needs_read_fill = 1;
+        }
+
+        return res;
+}
+
+
+static struct dentry *step_down(struct dentry *dir, const char * name)
+{
+        struct dentry * de;
+
+        if (dir == NULL || dir->d_inode == NULL)
+                return NULL;
+
+        mutex_lock(&dir->d_inode->i_mutex);
+        de = lookup_one_len(name, dir, strlen(name));
+        mutex_unlock(&dir->d_inode->i_mutex);
+        dput(dir);
+        if (IS_ERR(de))
+                return NULL;
+        if (de->d_inode == NULL) {
+                dput(de);
+                return NULL;
+        }
+        return de;
+}
+
+void sysfs_notify(struct kobject * k, char *dir, char *attr)
+{
+        struct dentry *de = k->dentry;
+        if (de)
+                dget(de);
+        if (de && dir)
+                de = step_down(de, dir);
+        if (de && attr)
+                de = step_down(de, attr);
+        if (de) {
+                struct sysfs_dirent * sd = de->d_fsdata;
+                if (sd)
+                        atomic_inc(&sd->s_event);
+                wake_up_interruptible(&k->poll);
+                dput(de);
+        }
+}
+EXPORT_SYMBOL_GPL(sysfs_notify);
+
 const struct file_operations sysfs_file_operations = {
         .read           = sysfs_read_file,
         .write          = sysfs_write_file,
         .llseek         = generic_file_llseek,
         .open           = sysfs_open_file,
         .release        = sysfs_release,
+        .poll           = sysfs_poll,
 };