diff options
Diffstat (limited to 'Documentation/filesystems/relay.txt')
| -rw-r--r-- | Documentation/filesystems/relay.txt | 16 |
1 files changed, 13 insertions, 3 deletions
diff --git a/Documentation/filesystems/relay.txt b/Documentation/filesystems/relay.txt index 7fbb6ffe576..33e2f369473 100644 --- a/Documentation/filesystems/relay.txt +++ b/Documentation/filesystems/relay.txt @@ -31,7 +31,7 @@ Semantics Each relay channel has one buffer per CPU, each buffer has one or more sub-buffers. Messages are written to the first sub-buffer until it is -too full to contain a new message, in which case it it is written to +too full to contain a new message, in which case it is written to the next (if available). Messages are never split across sub-buffers. At this point, userspace can be notified so it empties the first sub-buffer, while the kernel continues writing to the next. @@ -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 @@ -294,6 +294,16 @@ 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' --------------- @@ -351,7 +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 |