[PATCH] Relay: add CPU hotplug support

Mathieu originally needed to add this for tracing Xen, but it's something
that's needed for any application that can be tracing while cpus are added.

unplug isn't supported by this patch.  The thought was that at minumum a new
buffer needs to be added when a cpu comes up, but it wasn't worth the effort
to remove buffers on cpu down since they'd be freed soon anyway when the
channel was closed.

[zanussi@us.ibm.com: avoid lock_cpu_hotplug deadlock]
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@polymtl.ca>
Cc: Tom Zanussi <zanussi@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 7 insertions, 2 deletions

diff --git a/include/linux/relay.h b/include/linux/relay.h
index c6a48bfc8b14..759a0f97bec2 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -24,7 +24,7 @@
 /*
  * Tracks changes to rchan/rchan_buf structs
  */
-#define RELAYFS_CHANNEL_VERSION         6
+#define RELAYFS_CHANNEL_VERSION         7
 
 /*
  * Per-cpu relay channel buffer
@@ -64,6 +64,10 @@ struct rchan
         void *private_data;             /* for user-defined data */
         size_t last_toobig;             /* tried to log event > subbuf size */
         struct rchan_buf *buf[NR_CPUS]; /* per-cpu channel buffers */
+        int is_global;                  /* One global buffer ? */
+        struct list_head list;          /* for channel list */
+        struct dentry *parent;          /* parent dentry passed to open */
+        char base_filename[NAME_MAX];   /* saved base filename */
 };
 
 /*
@@ -162,7 +166,8 @@ struct rchan *relay_open(const char *base_filename,
                          struct dentry *parent,
                          size_t subbuf_size,
                          size_t n_subbufs,
-                         struct rchan_callbacks *cb);
+                         struct rchan_callbacks *cb,
+                         void *private_data);
 extern void relay_close(struct rchan *chan);
 extern void relay_flush(struct rchan *chan);
 extern void relay_subbufs_consumed(struct rchan *chan,