From: Mathieu Desnoyers Date: Thu, 11 May 2017 21:53:58 +0000 (-0400) Subject: Fix: use "flush empty" ioctl for snapshots X-Git-Tag: v2.9.5~7 X-Git-Url: http://git.liburcu.org/?p=lttng-tools.git;a=commitdiff_plain;h=612b8ed86aab0cd7549a433c50ecc9e999227077 Fix: use "flush empty" ioctl for snapshots When the flush empty ioctl is available, use it to produce an empty packet at the end of the snapshot, which ensures the stream intersection feature works. If this specific ioctl is not available, fallback on the "flush" ioctl, which does not produce empty packets. In that situation, there were two prior behaviors possible for lttng-modules: earlier versions implement a "snapshot" command which does not perform an implicit "flush_empty". In that case, the stream intersection feature may not be reliable. In more recent lttng-modules versions (included stable branch) which did not implement the flush_empty ioctl, the snapshot ioctl implicitly performed a flush_empty, which makes the stream intersection feature work, but has side-effects on the snapshot ioctl performed by the live timer (produces a stream of empty packets in live mode). [ Please apply to master, 2.10, 2.9, 2.8 branches. ] Signed-off-by: Mathieu Desnoyers Signed-off-by: Jérémie Galarneau --- diff --git a/src/common/kernel-consumer/kernel-consumer.c b/src/common/kernel-consumer/kernel-consumer.c index 5a8157eb5..4633db382 100644 --- a/src/common/kernel-consumer/kernel-consumer.c +++ b/src/common/kernel-consumer/kernel-consumer.c @@ -185,9 +185,20 @@ int lttng_kconsumer_snapshot_channel(uint64_t key, char *path, channel->streams_sent_to_relayd = true; } - ret = kernctl_buffer_flush(stream->wait_fd); + ret = kernctl_buffer_flush_empty(stream->wait_fd); if (ret < 0) { - ERR("Failed to flush kernel stream"); + /* + * Doing a buffer flush which does not take into + * account empty packets. This is not perfect + * for stream intersection, but required as a + * fall-back when "flush_empty" is not + * implemented by lttng-modules. + */ + ret = kernctl_buffer_flush(stream->wait_fd); + if (ret < 0) { + ERR("Failed to flush kernel stream"); + goto end_unlock; + } goto end_unlock; } diff --git a/src/common/kernel-ctl/kernel-ctl.c b/src/common/kernel-ctl/kernel-ctl.c index f58aef738..bc52c3e5d 100644 --- a/src/common/kernel-ctl/kernel-ctl.c +++ b/src/common/kernel-ctl/kernel-ctl.c @@ -408,6 +408,11 @@ int kernctl_buffer_flush(int fd) return LTTNG_IOCTL_CHECK(fd, RING_BUFFER_FLUSH); } +int kernctl_buffer_flush_empty(int fd) +{ + return LTTNG_IOCTL_CHECK(fd, RING_BUFFER_FLUSH_EMPTY); +} + /* returns the version of the metadata. */ int kernctl_get_metadata_version(int fd, uint64_t *version) { diff --git a/src/common/kernel-ctl/kernel-ctl.h b/src/common/kernel-ctl/kernel-ctl.h index a8c27dd3a..97b3128d3 100644 --- a/src/common/kernel-ctl/kernel-ctl.h +++ b/src/common/kernel-ctl/kernel-ctl.h @@ -92,6 +92,7 @@ int kernctl_get_subbuf(int fd, unsigned long *pos); int kernctl_put_subbuf(int fd); int kernctl_buffer_flush(int fd); +int kernctl_buffer_flush_empty(int fd); int kernctl_get_metadata_version(int fd, uint64_t *version); /* index */ diff --git a/src/common/kernel-ctl/kernel-ioctl.h b/src/common/kernel-ctl/kernel-ioctl.h index 2ade00cd1..070357cc6 100644 --- a/src/common/kernel-ctl/kernel-ioctl.h +++ b/src/common/kernel-ctl/kernel-ioctl.h @@ -47,10 +47,12 @@ #define RING_BUFFER_GET_MMAP_LEN _IOR(0xF6, 0x0A, unsigned long) /* returns the offset of the subbuffer belonging to the mmap reader. */ #define RING_BUFFER_GET_MMAP_READ_OFFSET _IOR(0xF6, 0x0B, unsigned long) -/* flush the current sub-buffer */ +/* Flush the current sub-buffer, if non-empty. */ #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) +/* Flush the current sub-buffer, even if empty. */ +#define RING_BUFFER_FLUSH_EMPTY _IO(0xF6, 0x0F) /* returns the timestamp begin of the current sub-buffer */ #define LTTNG_RING_BUFFER_GET_TIMESTAMP_BEGIN _IOR(0xF6, 0x20, uint64_t)