Trace events outside the global mutex cannot be used with the simple
trace backend since it is not thread-safe. There is no check to prevent
them being enabled so people sometimes learn this the hard way.
This patch restructures the simple trace backend with a ring buffer
suitable for multiple concurrent writers. A writeout thread empties the
trace buffer when threshold fill levels are reached. Should the
writeout thread be unable to keep up with trace generation, records will
simply be dropped.
Each time events are dropped a special record is written to the trace
file indicating how many events were dropped. The event ID is
0xfffffffffffffffe and its signature is dropped(uint32_t count).
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
The following additions to the tracing documentation are included:
1. Move "stderr" backend documentation to top-level and out of "simple"
backend. Include hints on when this backend is useful.
2. Document the "simple" backend thread-safety limitation.
3. Document the "dtrace" backend for SystemTap.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
This backend sends trace events to standard error output during the emulation.
Also add a "--list-backends" option to tracetool, so configure script can
display the list of available backends.
Signed-off-by: Fabien Chouteau <chouteau@adacore.com>
Acked-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
Document the restriction that format strings must begin and end with
double quotes. This is for easy parsing since we don't run cpp over
trace-events.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
It is not portable to use "%ld" for int64_t because int64_t may have
type long on 64-bit platforms and long long on 32-bit platforms. Use
the standard library PRId64 macros to keep format strings portable.
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: Blue Swirl <blauwirbel@gmail.com>
