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>
---
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
|