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From: Slavomir Kaslev <kaslevs@vmware.com>
To: rostedt@goodmis.org
Cc: linux-trace-devel@vger.kernel.org
Subject: [PATCH v15 07/13] trace-cmd: Use splice(2) for vsockets if available
Date: Tue,  8 Oct 2019 11:15:31 +0300
Message-ID: <20191008081537.11536-8-kaslevs@vmware.com> (raw)
In-Reply-To: <20191008081537.11536-1-kaslevs@vmware.com>

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@vmware.com>
---
 tracecmd/trace-record.c | 56 +++++++++++++++++++++++++++++++++++++++--
 1 file changed, 54 insertions(+), 2 deletions(-)

diff --git a/tracecmd/trace-record.c b/tracecmd/trace-record.c
index 79b39af..b974d09 100644
--- a/tracecmd/trace-record.c
+++ b/tracecmd/trace-record.c
@@ -2916,12 +2916,61 @@ 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 -errno;
+
+	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)
@@ -3125,13 +3174,16 @@ create_recorder_instance(struct buffer_instance *instance, const char *file, int
 
 	if (is_guest(instance)) {
 		int fd;
+		unsigned int flags;
 
 		fd = open_vsock(instance->cid, instance->client_ports[cpu]);
 		if (fd < 0)
 			die("Failed to connect to agent");
 
-		return tracecmd_create_recorder_virt(
-			file, cpu, recorder_flags | TRACECMD_RECORD_NOSPLICE, fd);
+		flags = recorder_flags;
+		if (!can_splice_read_vsock())
+			flags |= TRACECMD_RECORD_NOSPLICE;
+		return tracecmd_create_recorder_virt(file, cpu, flags, fd);
 	}
 
 	if (brass)
-- 
2.20.1


  parent reply index

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-08  8:15 [PATCH v15 00/13] Add VM kernel tracing over vsockets and FIFOs Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 01/13] trace-cmd: Make ports unsigned int Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 02/13] trace-cmd: Detect if vsockets are available Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 03/13] trace-cmd: Add tracecmd_create_recorder_virt() function Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 04/13] trace-cmd: Add VM tracing protocol messages Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 05/13] trace-cmd: Add buffer instance flags for tracing in guest and agent context Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 06/13] trace-cmd: Add VM kernel tracing over vsockets transport Slavomir Kaslev
2019-10-08  8:15 ` Slavomir Kaslev [this message]
2019-10-08  8:15 ` [PATCH v15 08/13] trace-cmd: Switch stop recording signal to SIGUSR1 Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 09/13] trace-cmd: Add `trace-cmd setup-guest` command Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 10/13] trace-cmd: Try to autodetect number of guest CPUs in setup-guest if not specified Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 11/13] trace-cmd: Add setup-guest flag for attaching FIFOs to the guest VM config Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 12/13] trace-cmd: Add VM kernel tracing over FIFO transport Slavomir Kaslev
2019-10-08  8:15 ` [PATCH v15 13/13] trace-cmd: Add support for tracing VMware Workstation VMs by name Slavomir Kaslev

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