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

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>

1 files changed, 5 insertions, 0 deletions

diff --git a/include/linux/relay.h b/include/linux/relay.h
index 6cd8c4425fc7..953fc055e875 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -48,6 +48,7 @@ struct rchan_buf
         size_t *padding;                /* padding counts per sub-buffer */
         size_t prev_padding;            /* temporary variable */
         size_t bytes_consumed;          /* bytes consumed in cur read subbuf */
+        size_t early_bytes;             /* bytes consumed before VFS inited */
         unsigned int cpu;               /* this buf's cpu */
 } ____cacheline_aligned;
 
@@ -68,6 +69,7 @@ struct rchan
         int is_global;                  /* One global buffer ? */
         struct list_head list;          /* for channel list */
         struct dentry *parent;          /* parent dentry passed to open */
+        int has_base_filename;          /* has a filename associated? */
         char base_filename[NAME_MAX];   /* saved base filename */
 };
 
@@ -169,6 +171,9 @@ struct rchan *relay_open(const char *base_filename,
                          size_t n_subbufs,
                          struct rchan_callbacks *cb,
                          void *private_data);
+extern int relay_late_setup_files(struct rchan *chan,
+                                  const char *base_filename,
+                                  struct dentry *parent);
 extern void relay_close(struct rchan *chan);
 extern void relay_flush(struct rchan *chan);
 extern void relay_subbufs_consumed(struct rchan *chan,