[RFC PATCH 1/11] relay - Clean up relay_switch_subbuf() and make waking up consumers optional.

Tom Zanussi
2008-09-29T05:40:25Z

Clean up relay_switch_subbuf() and make waking up consumers optional.

Over time, relay_switch_subbuf() has accumulated some cruft - this
patch cleans it up and at the same time makes available some of it
available as common functions that any subbuf-switch implementor would
need (this is partially in preparation for the next patch, which makes
the subbuf-switch function completely replaceable). It also removes
the hard-coded reader wakeup and moves it into a replaceable callback
called notify_consumers(); this allows any given tracer to implement
consumer notification as it sees fit.

Signed-off-by: Tom Zanussi <zanussi@comcast.net>

---
include/linux/relay.h | 51 +++++++++++++++++++++++++++++++++++++++++++++++++
kernel/relay.c | 43 +++++++++++++++++++++++------------------
2 files changed, 75 insertions(+), 19 deletions(-)

diff --git a/include/linux/relay.h b/include/linux/relay.h
index 953fc05..17f0515 100644
--- a/include/linux/relay.h
+++ b/include/linux/relay.h
@@ -159,6 +159,15 @@ struct rchan_callbacks
* The callback should return 0 if successful, negative if not.
*/
int (*remove_buf_file)(struct dentry *dentry);
+
+ /*
+ * notify_consumers - new sub-buffer available, let consumers know
+ * @buf: the channel buffer
+ *
+ * Called during sub-buffer switch. Applications which don't
+ * want to notify anyone should implement an empty version.
+ */
+ void (*notify_consumers)(struct rchan_buf *buf);
};

/*
@@ -186,6 +195,48 @@ extern size_t relay_switch_subbuf(struct rchan_buf *buf,
size_t length);

/**
+ * relay_event_toobig - is event too big to fit in a sub-buffer?
+ * @buf: relay channel buffer
+ * @length: length of event
+ *
+ * Returns 1 if too big, 0 otherwise.
+ *
+ * switch_subbuf() helper function.
+ */
+static inline int relay_event_toobig(struct rchan_buf *buf, size_t length)
+{
+ return length > buf->chan->subbuf_size;
+}
+
+/**
+ * relay_update_filesize - increase relay file i_size by length
+ * @buf: relay channel buffer
+ * @length: length to add
+ *
+ * switch_subbuf() helper function.
+ */
+static inline void relay_update_filesize(struct rchan_buf *buf, size_t length)
+{
+ if (buf->dentry)
+ buf->dentry->d_inode->i_size += length;
+ else
+ buf->early_bytes += length;
+
+ smp_mb();
+}
+
+/**
+ * relay_inc_produced - increase number of sub-buffers produced by 1
+ * @buf: relay channel buffer
+ *
+ * switch_subbuf() helper function.
+ */
+static inline void relay_inc_produced(struct rchan_buf *buf)
+{
+ buf->subbufs_produced++;
+}
+
+/**
* relay_write - write data into the channel
* @chan: relay channel
* @data: data to be written
diff --git a/kernel/relay.c b/kernel/relay.c
index 8d13a78..53652f1 100644
--- a/kernel/relay.c
+++ b/kernel/relay.c
@@ -324,6 +324,21 @@ static int remove_buf_file_default_callback(struct dentry *dentry)
return -EINVAL;
}

+/*
+ * notify_consumers() default callback.
+ */
+static void notify_consumers_default_callback(struct rchan_buf *buf)
+{
+ if (waitqueue_active(&buf->read_wait))
+ /*
+ * Calling wake_up_interruptible() from here
+ * will deadlock if we happen to be logging
+ * from the scheduler (trying to re-grab
+ * rq->lock), so defer it.
+ */
+ __mod_timer(&buf->timer, jiffies + 1);
+}
+
/* relay channel default callbacks */
static struct rchan_callbacks default_channel_callbacks = {
.subbuf_start = subbuf_start_default_callback,
@@ -331,6 +346,7 @@ static struct rchan_callbacks default_channel_callbacks = {
.buf_unmapped = buf_unmapped_default_callback,
.create_buf_file = create_buf_file_default_callback,
.remove_buf_file = remove_buf_file_default_callback,
+ .notify_consumers = notify_consumers_default_callback,
};

/**
@@ -508,6 +524,8 @@ static void setup_callbacks(struct rchan *chan,
cb->create_buf_file = create_buf_file_default_callback;
if (!cb->remove_buf_file)
cb->remove_buf_file = remove_buf_file_default_callback;
+ if (!cb->notify_consumers)
+ cb->notify_consumers = notify_consumers_default_callback;
chan->cb = cb;
}

@@ -726,30 +744,17 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
void *old, *new;
size_t old_subbuf, new_subbuf;

- if (unlikely(length > buf->chan->subbuf_size))
+ if (unlikely(relay_event_toobig(buf, length)))
goto toobig;

if (buf->offset != buf->chan->subbuf_size + 1) {
buf->prev_padding = buf->chan->subbuf_size - buf->offset;
old_subbuf = buf->subbufs_produced % buf->chan->n_subbufs;
buf->padding[old_subbuf] = buf->prev_padding;
- buf->subbufs_produced++;
- if (buf->dentry)
- buf->dentry->d_inode->i_size +=
- buf->chan->subbuf_size -
- buf->padding[old_subbuf];
- else
- buf->early_bytes += buf->chan->subbuf_size -
- buf->padding[old_subbuf];
- smp_mb();
- if (waitqueue_active(&buf->read_wait))
- /*
- * Calling wake_up_interruptible() from here
- * will deadlock if we happen to be logging
- * from the scheduler (trying to re-grab
- * rq->lock), so defer it.
- */
- __mod_timer(&buf->timer, jiffies + 1);
+ relay_inc_produced(buf);
+ relay_update_filesize(buf, buf->chan->subbuf_size -
+ buf->padding[old_subbuf]);
+ buf->chan->cb->notify_consumers(buf);
}

old = buf->data;
@@ -763,7 +768,7 @@ size_t relay_switch_subbuf(struct rchan_buf *buf, size_t length)
buf->data = new;
buf->padding[new_subbuf] = 0;

- if (unlikely(length + buf->offset > buf->chan->subbuf_size))
+ if (unlikely(relay_event_toobig(buf, length + buf->offset)))
goto toobig;

return length;
--
1.5.3.5