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-rw-r--r--Documentation/filesystems/sysfs.txt9
-rw-r--r--fs/sysfs/file.c5
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