[lttng-dev] [RFC PATCH lttng-modules] Add RING_BUFFER_SNAPSHOT_SAMPLE_POSITIONS command

[Mathieu Desnoyers]

I'm adding the missing "compat" code as I merge.

Thanks,

Mathieu

----- On May 5, 2017, at 10:34 AM, Mathieu Desnoyers mathieu.desnoyers at efficios.com wrote:

> Merged into master, thanks!
> 
> Mathieu
> 
> ----- On May 4, 2017, at 5:25 PM, Jeremie Galarneau
> jeremie.galarneau at efficios.com wrote:
> 
>> There is no need to bump the LTTNG_MODULES_ABI_MINOR_VERSION
>> since the multiple wildcard feature introduced as part of the 2.10
>> release already bumps it from 2 to 3.
>> 
>> Signed-off-by: Jérémie Galarneau <jeremie.galarneau at efficios.com>
>> ---
>> lib/ringbuffer/frontend.h             |  4 ++++
>> lib/ringbuffer/ring_buffer_frontend.c | 31 +++++++++++++++++++++++++++++++
>> lib/ringbuffer/ring_buffer_vfs.c      |  3 +++
>> lib/ringbuffer/vfs.h                  |  6 ++++++
>> 4 files changed, 44 insertions(+)
>> 
>> diff --git a/lib/ringbuffer/frontend.h b/lib/ringbuffer/frontend.h
>> index 6ff1545..909abc2 100644
>> --- a/lib/ringbuffer/frontend.h
>> +++ b/lib/ringbuffer/frontend.h
>> @@ -106,6 +106,10 @@ extern void lib_ring_buffer_release_read(struct
>> lib_ring_buffer *buf);
>> extern int lib_ring_buffer_snapshot(struct lib_ring_buffer *buf,
>> 				    unsigned long *consumed,
>> 				    unsigned long *produced);
>> +extern int lib_ring_buffer_snapshot_sample_positions(
>> +				    struct lib_ring_buffer *buf,
>> +				    unsigned long *consumed,
>> +				    unsigned long *produced);
>> extern void lib_ring_buffer_move_consumer(struct lib_ring_buffer *buf,
>> 					  unsigned long consumed_new);
>> 
>> diff --git a/lib/ringbuffer/ring_buffer_frontend.c
>> b/lib/ringbuffer/ring_buffer_frontend.c
>> index 68b6238..a477832 100644
>> --- a/lib/ringbuffer/ring_buffer_frontend.c
>> +++ b/lib/ringbuffer/ring_buffer_frontend.c
>> @@ -1120,6 +1120,37 @@ nodata:
>> EXPORT_SYMBOL_GPL(lib_ring_buffer_snapshot);
>> 
>> /**
>> + * Performs the same function as lib_ring_buffer_snapshot(), but the positions
>> + * are saved regardless of whether the consumed and produced positions are
>> + * in the same subbuffer.
>> + * @buf: ring buffer
>> + * @consumed: consumed byte count indicating the last position read
>> + * @produced: produced byte count indicating the last position written
>> + *
>> + * This function is meant to provide information on the exact producer and
>> + * consumer positions without regard for the "snapshot" feature.
>> + */
>> +int lib_ring_buffer_snapshot_sample_positions(struct lib_ring_buffer *buf,
>> +		unsigned long *consumed, unsigned long *produced)
>> +{
>> +	struct channel *chan = buf->backend.chan;
>> +	const struct lib_ring_buffer_config *config = &chan->backend.config;
>> +
>> +	smp_rmb();
>> +	*consumed = atomic_long_read(&buf->consumed);
>> +	/*
>> +	 * No need to issue a memory barrier between consumed count read and
>> +	 * write offset read, because consumed count can only change
>> +	 * concurrently in overwrite mode, and we keep a sequence counter
>> +	 * identifier derived from the write offset to check we are getting
>> +	 * the same sub-buffer we are expecting (the sub-buffers are atomically
>> +	 * "tagged" upon writes, tags are checked upon read).
>> +	 */
>> +	*produced = v_read(config, &buf->offset);
>> +	return 0;
>> +}
>> +
>> +/**
>>  * lib_ring_buffer_put_snapshot - move consumed counter forward
>>  *
>>  * Should only be called from consumer context.
>> diff --git a/lib/ringbuffer/ring_buffer_vfs.c b/lib/ringbuffer/ring_buffer_vfs.c
>> index 15da212..603dcfc 100644
>> --- a/lib/ringbuffer/ring_buffer_vfs.c
>> +++ b/lib/ringbuffer/ring_buffer_vfs.c
>> @@ -202,6 +202,9 @@ long lib_ring_buffer_ioctl(struct file *filp, unsigned int
>> cmd,
>> 			lib_ring_buffer_switch_remote_empty(buf);
>> 		return lib_ring_buffer_snapshot(buf, &buf->cons_snapshot,
>> 					    &buf->prod_snapshot);
>> +	case RING_BUFFER_SNAPSHOT_SAMPLE_POSITIONS:
>> +		return lib_ring_buffer_snapshot_sample_positions(buf,
>> +				&buf->cons_snapshot, &buf->prod_snapshot);
>> 	case RING_BUFFER_SNAPSHOT_GET_CONSUMED:
>> 		return put_ulong(buf->cons_snapshot, arg);
>> 	case RING_BUFFER_SNAPSHOT_GET_PRODUCED:
>> diff --git a/lib/ringbuffer/vfs.h b/lib/ringbuffer/vfs.h
>> index 5444a4b..8a89caf 100644
>> --- a/lib/ringbuffer/vfs.h
>> +++ b/lib/ringbuffer/vfs.h
>> @@ -115,6 +115,12 @@ ssize_t vfs_lib_ring_buffer_splice_read(struct file *in,
>> loff_t *ppos,
>> #define RING_BUFFER_FLUSH			_IO(0xF6, 0x0C)
>> /* Get the current version of the metadata cache (after a get_next). */
>> #define RING_BUFFER_GET_METADATA_VERSION	_IOR(0xF6, 0x0D, uint64_t)
>> +/*
>> + * Get a snapshot of the current ring buffer producer and consumer positions,
>> + * regardless of whether or not the two positions are contained within the same
>> + * sub-buffer.
>> + */
>> +#define RING_BUFFER_SNAPSHOT_SAMPLE_POSITIONS	_IO(0xF6, 0x0E)
>> 
>> #ifdef CONFIG_COMPAT
>> /* Get a snapshot of the current ring buffer producer and consumer positions */
>> --
>> 2.12.2
> 
> --
> Mathieu Desnoyers
> EfficiOS Inc.
> http://www.efficios.com

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com