perf kvm: Support using -f to override perf.data.guest file ownership

Enable perf kvm to use perf.data.guest when it is not owned by current
user or root.

Example:

# perf kvm stat record ls
# chown Yunlong.Song:Yunlong.Song perf.data.guest
# ls -al perf.data.guest
-rw------- 1 Yunlong.Song Yunlong.Song 4128937 Apr 2 11:05 perf.data.guest
# id
uid=0(root) gid=0(root) groups=0(root),64(pkcs11)

Before this patch:

# perf kvm stat report
File perf.data.guest not owned by current user or root (use -f to override)
Initializing perf session failed
# perf kvm stat report -f
Error: unknown switch `f'

usage: perf kvm stat report [<options>]

--event <report event>
event for reporting: vmexit, mmio (x86 only),
ioport (x86 only)
--vcpu <n> vcpu id to report
-k, --key <sort-key> key for sorting: sample(sort by samples
number) time (sort by avg time)
-p, --pid <pid> analyze events only for given process id(s)

As shown above, the -f option does not work at all.

After this patch:

# perf kvm stat report
File perf.data.guest not owned by current user or root (use -f to override)
Initializing perf session failed
# perf kvm stat report -f
Analyze events for all VMs, all VCPUs:

VM-EXIT Samples Samples% Time% Min Time Max Time Avg time

Total Samples:0, Total events handled time:0.00us.

As shown above, the -f option really works now. Since we have not
launched any KVM related process, the result shows 0 sample here.

Signed-off-by: Yunlong Song <[e-mail]>
Tested-by: Arnaldo Carvalho de Melo <[e-mail]>
Cc: Paul Mackerras <[e-mail]>
Cc: Peter Zijlstra <[e-mail]>
Cc: Wang Nan <[e-mail]>
Link: http://lkml.kernel.org/r/[e-mail]
Signed-off-by: Arnaldo Carvalho de Melo <[e-mail]>

tools/perf/builtin-kvm.c

···
 	struct perf_data_file file = {
 		.path = kvm->file_name,
 		.mode = PERF_DATA_MODE_READ,
+		.force = kvm->force,
 	};
 
 	kvm->tool = eops;
···
 			    " time (sort by avg time)"),
 		OPT_STRING('p', "pid", &kvm->opts.target.pid, "pid",
 			   "analyze events only for given process id(s)"),
+		OPT_BOOLEAN('f', "force", &kvm->force, "don't complain, do it"),
 		OPT_END()
 	};
 

tools/perf/util/kvm-stat.h

···
 	int timerfd;
 	unsigned int display_time;
 	bool live;
+	bool force;
 };
 
 struct kvm_reg_events_ops {