Merge commit 'v2.6.27-rc8' into x86/setup

[pandora-kernel.git] / Documentation / filesystems / relay.txt

diff --git a/Documentation/filesystems/relay.txt b/Documentation/filesystems/relay.txt
index d6788da..510b722 100644 (file)
--- a/Documentation/filesystems/relay.txt
+++ b/Documentation/filesystems/relay.txt
@@ -140,7 +140,7 @@ close()     decrements the channel buffer's refcount.  When the refcount
 In order for a user application to make use of relay files, the
 host filesystem must be mounted.  For example,
 
-       mount -t debugfs debugfs /debug
+       mount -t debugfs debugfs /sys/kernel/debug
 
 NOTE:   the host filesystem doesn't need to be mounted for kernel
        clients to create or use channels - it only needs to be
@@ -157,7 +157,7 @@ TBD(curr. line MT:/API/)
   channel management functions:
 
     relay_open(base_filename, parent, subbuf_size, n_subbufs,
-               callbacks)
+               callbacks, private_data)
     relay_close(chan)
     relay_flush(chan)
     relay_reset(chan)
@@ -251,7 +251,7 @@ static struct rchan_callbacks relay_callbacks =
 
 And an example relay_open() invocation using them:
 
-  chan = relay_open("cpu", NULL, SUBBUF_SIZE, N_SUBBUFS, &relay_callbacks);
+  chan = relay_open("cpu", NULL, SUBBUF_SIZE, N_SUBBUFS, &relay_callbacks, NULL);
 
 If the create_buf_file() callback fails, or isn't defined, channel
 creation and thus relay_open() will fail.
@@ -289,6 +289,21 @@ they use the proper locking for such a buffer, either by wrapping
 writes in a spinlock, or by copying a write function from relay.h and
 creating a local version that internally does the proper locking.
 
+The private_data passed into relay_open() allows clients to associate
+user-defined data with a channel, and is immediately available
+(including in create_buf_file()) via chan->private_data or
+buf->chan->private_data.
+
+Buffer-only channels
+--------------------
+
+These channels have no files associated and can be created with
+relay_open(NULL, NULL, ...). Such channels are useful in scenarios such
+as when doing early tracing in the kernel, before the VFS is up. In these
+cases, one may open a buffer-only channel and then call
+relay_late_setup_files() when the kernel is ready to handle files,
+to expose the buffered data to the userspace.
+
 Channel 'modes'
 ---------------
 
@@ -346,7 +361,7 @@ If the current buffer is full, i.e. all sub-buffers remain unconsumed,
 the callback returns 0 to indicate that the buffer switch should not
 occur yet, i.e. until the consumer has had a chance to read the
 current set of ready sub-buffers.  For the relay_buf_full() function
-to make sense, the consumer is reponsible for notifying the relay
+to make sense, the consumer is responsible for notifying the relay
 interface when sub-buffers have been consumed via
 relay_subbufs_consumed().  Any subsequent attempts to write into the
 buffer will again invoke the subbuf_start() callback with the same