2 files changed, 9 insertions, 5 deletions

diff --git a/Documentation/filesystems/sysfs.txt b/Documentation/filesystems/sysfs.txt
index 4598ef7b622b..7f27b8f840d0 100644
--- a/Documentation/filesystems/sysfs.txt
+++ b/Documentation/filesystems/sysfs.txt
@@ -176,8 +176,10 @@ implementations:
   Recall that an attribute should only be exporting one value, or an
   array of similar values, so this shouldn't be that expensive. 
 
-  This allows userspace to do partial reads and seeks arbitrarily over
-  the entire file at will. 
+  This allows userspace to do partial reads and forward seeks
+  arbitrarily over the entire file at will. If userspace seeks back to
+  zero or does a pread(2) with an offset of '0' the show() method will
+  be called again, rearmed, to fill the buffer.
 
 - On write(2), sysfs expects the entire buffer to be passed during the
   first write. Sysfs then passes the entire buffer to the store()
@@ -192,6 +194,9 @@ implementations:
 
 Other notes:
 
+- Writing causes the show() method to be rearmed regardless of current
+  file position.
+
 - The buffer will always be PAGE_SIZE bytes in length. On i386, this
   is 4096. 
 
diff --git a/fs/sysfs/file.c b/fs/sysfs/file.c
index a859c32ff93a..ade9a7e6a757 100644
--- a/fs/sysfs/file.c
+++ b/fs/sysfs/file.c
@@ -129,7 +129,7 @@ sysfs_read_file(struct file *file, char __user *buf, size_t count, loff_t *ppos)
         ssize_t retval = 0;
 
         mutex_lock(&buffer->mutex);
-        if (buffer->needs_read_fill) {
+        if (buffer->needs_read_fill || *ppos == 0) {
                 retval = fill_read_buffer(file->f_path.dentry,buffer);
                 if (retval)
                         goto out;
@@ -410,8 +410,7 @@ static int sysfs_release(struct inode *inode, struct file *filp)
  * 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'.
+ * need to close and re-open the file, or seek to 0 and read again.
  * 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 (Neither 'poll' nor 'select' return