On Mon, Jul 11, 2016 at 01:17:09PM -0700, Andrew Morton wrote: > On Mon, 11 Jul 2016 12:47:36 +0530 akash.g...@intel.com wrote: > > > From: Akash Goel <akash.g...@intel.com> > > > > The following patch added support to use channels with no associated files. > > relay: add buffer-only channels; useful for early logging > > hm, 8 years ago. Normally we refer to previous commits using the form > 20d8b67c06fa5e74f44e ("relay: add buffer-only channels; useful for > early logging"). But this one is so old that we should inform readers > about its vintage, so this form: > > commit 20d8b67c06fa5e74f44e80b0a0fd68c8327f7c6a > Author: Eduard - Gabriel Munteanu <eduard.munte...@linux360.ro> > Date: Fri Jul 25 19:45:12 2008 -0700 > > relay: add buffer-only channels; useful for early logging > > would be better. > > > This is useful when the exact location of relay file is not known or the > > the parent directory of relay file is not available, while creating the > > channel and the logging has to start right from the boot. > > > > But there was no provision to use global mode with buffer-only channels, > > which is added by this patch, without modifying the interface where > > initially > > there will be a dummy invocation of create_buf_file callback through which > > kernel client can convey the need of a global buffer. > > > > For the use case where drivers/kernel clients want a simple interface for > > the > > userspace, which enables them to capture data/logs from relay file in order > > & > > without any post processing, support of Global buffer mode is warranted. > > > > ... > > > > @@ -706,6 +727,7 @@ int relay_late_setup_files(struct rchan *chan, > > > > return err; > > } > > +EXPORT_SYMBOL_GPL(relay_late_setup_files); > > The export is unneeded and undocumented.
Something like: diff --git a/kernel/relay.c b/kernel/relay.c index 04d7cf3ef8cf..fd86f01de4b2 100644 --- a/kernel/relay.c +++ b/kernel/relay.c @@ -562,6 +562,10 @@ static int relay_hotcpu_callback(struct notifier_block *nb, * attributes specified. The created channel buffer files * will be named base_filename0...base_filenameN-1. File * permissions will be %S_IRUSR. + * + * If opening a buffer (@parent = NULL) that you later wish to register + * in a filesystem, call relay_late_setup_files() once the @parent dentry + * is available. */ struct rchan *relay_open(const char *base_filename, struct dentry *parent, @@ -640,8 +644,12 @@ static void __relay_set_buf_dentry(void *info) * * Returns 0 if successful, non-zero otherwise. * - * Use to setup files for a previously buffer-only channel. - * Useful to do early tracing in kernel, before VFS is up, for example. + * Use to setup files for a previously buffer-only channel created + * by relay_open() with a NULL parent dentry. + * + * For example, this is useful for perfomring early tracing in kernel, + * before VFS is up and then exposing the early results once the dentry + * is available. */ int relay_late_setup_files(struct rchan *chan, const char *base_filename, with a comment in the changelog that modules using relay_open() in early init also want to later register their buffer-only relays once debugfs is available, e.g. i915. -Chris -- Chris Wilson, Intel Open Source Technology Centre