trace: handle tracefs path truncation

trace: handle tracefs path truncation

If the tracefs mountpoint has a very long path we may exceed PATH_MAX.
This is a system misconfiguration and the user must resolve it so that
applications can perform path-based system calls successfully.

This issue does not occur on real-world systems since tracefs is mounted
on /sys/kernel/debug/tracing/, but the compiler is smart enough to
foresee the possibility and warn about the unchecked snprintf(3) return
value.  This patch fixes the compiler warning.

Reported-by: Markus Armbruster <[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>
Reviewed-by: Markus Armbruster <[email protected]>
Reviewed-by: Liam Merwick <[email protected]>
Message-id: 20190321170831[email protected]
Message-Id: <20190321170831[email protected]>
Signed-off-by: Stefan Hajnoczi <[email protected]>