[PATCH] sysfs: Allow sysfs attribute files to be pollable

It works like this:
  Open the file
  Read all the contents.
  Call poll requesting POLLERR or POLLPRI (so select/exceptfds works)
  When poll returns,
     close the file and go to top of loop.
   or lseek to start of file and go back to the 'read'.

Events are signaled by an object manager calling
   sysfs_notify(kobj, dir, attr);

If the dir is non-NULL, it is used to find a subdirectory which
contains the attribute (presumably created by sysfs_create_group).

This has a cost of one int  per attribute, one wait_queuehead per kobject,
one int per open file.

The name "sysfs_notify" may be confused with the inotify
functionality.  Maybe it would be nice to support inotify for sysfs
attributes as well?

This patch also uses sysfs_notify to allow /sys/block/md*/md/sync_action
to be pollable

Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index 4cb1214ec290..dcd0623be892 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -24,6 +24,7 @@
 #include <linux/rwsem.h>
 #include <linux/kref.h>
 #include <linux/kernel.h>
+#include <linux/wait.h>
 #include <asm/atomic.h>
 
 #define KOBJ_NAME_LEN                   20
@@ -56,6 +57,7 @@ struct kobject {
         struct kset             * kset;
         struct kobj_type        * ktype;
         struct dentry           * dentry;
+        wait_queue_head_t       poll;
 };
 
 extern int kobject_set_name(struct kobject *, const char *, ...)