The ltt_control command "setMarkerEnable" allows one to (globally) enable or
disable a marker on the target machine through a line like:
> tcf ltt_control setMarkerEnable "kernel" "0" "irq_state/interrupt" true
However, if one tries to enable an already-enabled marker, one gets:
{"Code":1,"Time":1311277723370,"Format":"Unknown error 131073"} "Kernel : Can't
enable marker irq_state/interrupt : File exists"
Similarly, if one tries to disable an already-disabled marker, one gets:
{"Code":1,"Time":1311278390400,"Format":"Unknown error 131073"} "Kernel : Can't
enable marker irq_state/interrupt : No such file or directory"
The expected behaviour in both cases is a simple success. There is no
reason for the errors.
What's remarkable here is that the errors are at once the same (same unknown
error code) and different ("File exists" vs. " No such file or directory").
I've narrowed down the problem to the LTTng TCF agent plug-in's
lttctlkerninterface.c and the methods ltt_kern_set_marker_enable and
ltt_kern_sendop. The former prepares the target file name for the latter. The
enabled/disabled state of the marker is managed through the
/sys/kernel/debug/ltt/markers/irq_state/interrupt/enable file, which contains
"1" or "0".
I'm really puzzled by this bug: the behaviour is deterministically
consistent but the error messages make no sense (the target file is never
missing, and what of the "File exists" message??).
The offending code is:
static int ltt_kern_sendop(const char *fname, const char *op)
{
int fd;
if (!fname) {
fprintf(stderr, "%s: args invalid\n", __func__);
return 1;
}
fd = open(fname, O_WRONLY);
if (fd == -1) {
fprintf(stderr, "%s: open %s failed: %s\n", __func__, fname,
strerror(errno));
return errno;
}
if (write(fd, op, strlen(op)) == -1) {
int ret = errno;
fprintf(stderr, "%s: write %s to %s failed: %s\n", __func__, op, fname,
strerror(errno));
close(fd);
return ret;
}
close(fd);
return 0;
}
The write(fd, op, strlen(op)) fails in both the double-enabling ("write 1 to
/sys/kernel/debug/ltt/markers/irq_state/interrupt/enable failed: File exists")
and double-disabling ("write 0 to
/sys/kernel/debug/ltt/markers/irq_state/interrupt/enable failed: No such file
or directory") cases.
Anyone have a clue what is going on?
Daniel U. Thibault
R & D pour la défense Canada - Valcartier (RDDC Valcartier) / Defence R&D
Canada - Valcartier (DRDC Valcartier)
Système de systèmes (SdS) / System of Systems (SoS)
Solutions informatiques et expérimentations (SIE) / Computing Solutions and
Experimentations (CSE)
2459 Boul. Pie XI Nord
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CANADA
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Gouvernement du Canada / Government of Canada
<http://www.valcartier.drdc-rddc.gc.ca/
<http://www.valcartier.drdc-rddc.gc.ca/> >
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