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Subject[RFC PATCH 4/6] relay: add relay_reserve_cpu()
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This patch adds the ability to explicitly specify the per-cpu buffer
to reserve space in. Needed for early DTI tracing.

Signed-off-by: Tom Zanussi <zanussi@us.ibm.com>
Signed-off-by: David Wilder <dwilder@us.ibm.com>
---
relay.h | 33 +++++++++++++++++++++++++++++++++
1 file changed, 33 insertions(+)

diff --git a/include/linux/relay.h b/include/linux/relay.h
index 6caedef..37a7306 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -269,6 +269,39 @@ static inline void *relay_reserve(struct rchan *chan, size_t length)
}

/**
+ * relay_reserve_cpu - reserve slot in given cpu's channel buffer
+ * @chan: relay channel
+ * @length: number of bytes to reserve
+ * @cpu: cpu to log to
+ *
+ * Returns pointer to reserved slot, NULL if full.
+ *
+ * Reserves a slot in the given cpu's channel buffer.
+ * Does not protect the buffer at all - caller must provide
+ * appropriate synchronization.
+ *
+ * NOTE: this is almost certainly not the function you want -
+ * use relay_reserve() instead for normal logging. This version
+ * is specialized for things like early tracing.
+ */
+static inline void *relay_reserve_cpu(struct rchan *chan, size_t length,
+ unsigned int cpu)
+{
+ void *reserved;
+ struct rchan_buf *buf = chan->buf[cpu];
+
+ if (unlikely(buf->offset + length > buf->chan->subbuf_size)) {
+ length = relay_switch_subbuf(buf, length);
+ if (!length)
+ return NULL;
+ }
+ reserved = buf->data + buf->offset;
+ buf->offset += length;
+
+ return reserved;
+}
+
+/**
* subbuf_start_reserve - reserve bytes at the start of a sub-buffer
* @buf: relay channel buffer
* @length: number of bytes to reserve


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