The patch titled
Relay Reset Consumed
has been added to the -mm tree. Its filename is
relay-reset-consumed.patch
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------------------------------------------------------
Subject: Relay Reset Consumed
From: "David J. Wilder" <dwilder@xxxxxxxxxx>
Allow a relay channel to be reset i.e. unconsumed. Basically allows a
'rewind' function for flight-recorder tracing.
Signed-off-by: Tom Zanussi <zanussi@xxxxxxxxxx>
Signed-off-by: David Wilder <dwilder@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
Documentation/filesystems/relay.txt | 11 ++++
include/linux/relay.h | 1
kernel/relay.c | 58 +++++++++++++++++++++++---
3 files changed, 65 insertions(+), 5 deletions(-)
diff -puN Documentation/filesystems/relay.txt~relay-reset-consumed Documentation/filesystems/relay.txt
--- a/Documentation/filesystems/relay.txt~relay-reset-consumed
+++ a/Documentation/filesystems/relay.txt
@@ -161,6 +161,7 @@ TBD(curr. line MT:/API/)
relay_close(chan)
relay_flush(chan)
relay_reset(chan)
+ relay_reset_consumed(chan)
channel management typically called on instigation of userspace:
@@ -452,6 +453,16 @@ state without reallocating channel buffe
existing mappings. It should however only be called when it's safe to
do so, i.e. when the channel isn't currently being written to.
+The read(2) implementation always 'consumes' the bytes read,
+i.e. those bytes won't be available again to subsequent reads.
+Certain applications may nonetheless wish to allow the 'consumed' data
+to be re-read; relay_reset_consumed() is provided for that purpose -
+it resets the internal consumed counters for all buffers in the
+channel. For example, if a first set of reads 'drains' the channel,
+and then relay_reset_consumed() is called, a second set of reads will
+get the exact same data (assuming no new data was written between the
+first set of reads and the second).
+
Finally, there are a couple of utility callbacks that can be used for
different purposes. buf_mapped() is called whenever a channel buffer
is mmapped from user space and buf_unmapped() is called when it's
diff -puN include/linux/relay.h~relay-reset-consumed include/linux/relay.h
--- a/include/linux/relay.h~relay-reset-consumed
+++ a/include/linux/relay.h
@@ -175,6 +175,7 @@ extern void relay_subbufs_consumed(struc
unsigned int cpu,
size_t consumed);
extern void relay_reset(struct rchan *chan);
+extern void relay_reset_consumed(struct rchan *chan);
extern int relay_buf_full(struct rchan_buf *buf);
extern size_t relay_switch_subbuf(struct rchan_buf *buf,
diff -puN kernel/relay.c~relay-reset-consumed kernel/relay.c
--- a/kernel/relay.c~relay-reset-consumed
+++ a/kernel/relay.c
@@ -378,6 +378,57 @@ void relay_reset(struct rchan *chan)
}
EXPORT_SYMBOL_GPL(relay_reset);
+/**
+ * __relay_reset_consumed - reset a channel buffer's consumed count
+ * @buf: the channel buffer
+ *
+ * See relay_reset_consumed for description of effect.
+ */
+static void __relay_reset_consumed(struct rchan_buf *buf)
+{
+ size_t n_subbufs = buf->chan->n_subbufs;
+ size_t produced = buf->subbufs_produced;
+ size_t consumed = buf->subbufs_consumed;
+
+ if (produced < n_subbufs)
+ buf->subbufs_consumed = 0;
+ else {
+ consumed = produced - n_subbufs;
+ if (buf->offset)
+ consumed++;
+ buf->subbufs_consumed = consumed;
+ }
+ buf->bytes_consumed = 0;
+}
+
+/**
+ * relay_reset_consumed - reset the channel's consumed counts
+ * @chan: the channel
+ *
+ * This has the effect of making all data previously read (and
+ * not overwritten by subsequent writes) from a channel available
+ * for reading again.
+ *
+ * NOTE: Care should be taken that the channel isn't actually
+ * being used by anything when this call is made.
+ */
+void relay_reset_consumed(struct rchan *chan)
+{
+ unsigned int i;
+ struct rchan_buf *prev = NULL;
+
+ if (!chan)
+ return;
+
+ for (i = 0; i < NR_CPUS; i++) {
+ if (!chan->buf[i] || chan->buf[i] == prev)
+ break;
+ __relay_reset_consumed(chan->buf[i]);
+ prev = chan->buf[i];
+ }
+}
+EXPORT_SYMBOL_GPL(relay_reset_consumed);
+
/*
* relay_open_buf - create a new relay channel buffer
*
@@ -840,11 +891,8 @@ static int relay_file_read_avail(struct
return 1;
}
- if (unlikely(produced - consumed >= n_subbufs)) {
- consumed = produced - n_subbufs + 1;
- buf->subbufs_consumed = consumed;
- buf->bytes_consumed = 0;
- }
+ if (unlikely(produced - consumed >= n_subbufs))
+ __relay_reset_consumed(buf);
produced = (produced % n_subbufs) * subbuf_size + buf->offset;
consumed = (consumed % n_subbufs) * subbuf_size + buf->bytes_consumed;
_
Patches currently in -mm which might be from dwilder@xxxxxxxxxx are
relay-reset-consumed.patch
trace-code-and-documentation.patch
trace-sample.patch
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