Detect if splice(2) reading is supported for vsockets (Linux 4.20 and later) and use it, or fallback to read/write-ing otherwise. Signed-off-by: Slavomir Kaslev <kaslevs@xxxxxxxxxx> --- lib/trace-cmd/trace-recorder.c | 6 ++-- tracecmd/trace-record.c | 56 ++++++++++++++++++++++++++++++++-- 2 files changed, 56 insertions(+), 6 deletions(-) diff --git a/lib/trace-cmd/trace-recorder.c b/lib/trace-cmd/trace-recorder.c index 83a12f4..b750935 100644 --- a/lib/trace-cmd/trace-recorder.c +++ b/lib/trace-cmd/trace-recorder.c @@ -380,10 +380,8 @@ static long splice_data(struct tracecmd_recorder *recorder) ret = splice(recorder->brass[0], NULL, recorder->fd, NULL, read, recorder->fd_flags); if (ret < 0) { - if (errno != EAGAIN && errno != EINTR) { - warning("recorder error in splice output"); - return -1; - } + if (errno != EAGAIN && errno != EINTR) + return ret; return total_read; } else update_fd(recorder, ret); diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c index 3c28314..71176d9 100644 --- a/tracecmd/trace-record.c +++ b/tracecmd/trace-record.c @@ -2656,12 +2656,61 @@ static int open_vsock(unsigned int cid, unsigned int port) return sd; } + +static int try_splice_read_vsock(void) +{ + int ret, sd, brass[2]; + + sd = socket(AF_VSOCK, SOCK_STREAM, 0); + if (sd < 0) + return sd; + + ret = pipe(brass); + if (ret < 0) + goto out_close_sd; + + /* + * On kernels that don't support splice reading from vsockets + * this will fail with EINVAL, or ENOTCONN otherwise. + * Technically, it should never succeed but if it does, claim splice + * reading is supported. + */ + ret = splice(sd, NULL, brass[1], NULL, 10, 0); + if (ret < 0) + ret = errno != EINVAL; + else + ret = 1; + + close(brass[0]); + close(brass[1]); +out_close_sd: + close(sd); + return ret; +} + +static bool can_splice_read_vsock(void) +{ + static bool initialized, res; + + if (initialized) + return res; + + res = try_splice_read_vsock() > 0; + initialized = true; + return res; +} + #else static inline int open_vsock(unsigned int cid, unsigned int port) { die("vsock is not supported"); return -1; } + +static bool can_splice_read_vsock(void) +{ + return false; +} #endif static int do_accept(int sd) @@ -2866,13 +2915,16 @@ create_recorder_instance(struct buffer_instance *instance, const char *file, int if (instance->flags & BUFFER_FL_GUEST) { int sd; + unsigned int flags; sd = open_vsock(instance->cid, instance->client_ports[cpu]); if (sd < 0) die("Failed to connect to agent"); - return tracecmd_create_recorder_virt( - file, cpu, recorder_flags | TRACECMD_RECORD_NOSPLICE, sd); + flags = recorder_flags; + if (!can_splice_read_vsock()) + flags |= TRACECMD_RECORD_NOSPLICE; + return tracecmd_create_recorder_virt(file, cpu, flags, sd); } if (brass) -- 2.19.1
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