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relay: add buffer-only channels; useful for early logging

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Allows one to create and use a channel with no associated files.  Files
can be initialized later.  This is useful in scenarios such as logging in
early code, before VFS is up.  Therefore, such channels can be created and
used as soon as kmem_cache_init() completed.

This is needed by kmemtrace to do tracing in early kernel code.

[kosaki.motohiro@jp.fujitsu.com: build fix]
Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Cc: Tom Zanussi <tzanussi@gmail.com>
Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
Eduard - Gabriel Munteanu
2008-07-25 19:45:12 -07:00
committed by Linus Torvalds
parent 7babe8db99
commit 20d8b67c06
3 changed files with 156 additions and 29 deletions
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10
Documentation/filesystems/relay.txt
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@@ -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'
---------------