perf record: Put a copy of kcore into the perf.data directory

Add a new 'perf record' option '--kcore' which will put a copy of
/proc/kcore, kallsyms and modules into a perf.data directory. Note, that
without the --kcore option, output goes to a file as previously. The
tools' -o and -i options work with either a file name or directory name.

Example:

$ sudo perf record --kcore uname

$ sudo tree perf.data
perf.data
├── kcore_dir
│   ├── kallsyms
│   ├── kcore
│   └── modules
└── data

$ sudo perf script -v
build id event received for vmlinux: 1eaa285996affce2d74d8e66dcea09a80c9941de
build id event received for [vdso]: 8bbaf5dc62a9b644b4d4e4539737e104e4a84541
Samples for 'cycles' event do not have CPU attribute set. Skipping 'cpu' field.
Using CPUID GenuineIntel-6-8E-A
Using perf.data/kcore_dir/kcore for kernel data
Using perf.data/kcore_dir/kallsyms for symbols
perf 19058 506778.423729: 1 cycles: ffffffffa2caa548 native_write_msr+0x8 (vmlinux)
perf 19058 506778.423733: 1 cycles: ffffffffa2caa548 native_write_msr+0x8 (vmlinux)
perf 19058 506778.423734: 7 cycles: ffffffffa2caa548 native_write_msr+0x8 (vmlinux)
perf 19058 506778.423736: 117 cycles: ffffffffa2caa54a native_write_msr+0xa (vmlinux)
perf 19058 506778.423738: 2092 cycles: ffffffffa2c9b7b0 native_apic_msr_write+0x0 (vmlinux)
perf 19058 506778.423740: 37380 cycles: ffffffffa2f121d0 perf_event_addr_filters_exec+0x0 (vmlinux)
uname 19058 506778.423751: 582673 cycles: ffffffffa303a407 propagate_protected_usage+0x147 (vmlinux)
uname 19058 506778.423892: 2241841 cycles: ffffffffa2cae0c9 unwind_next_frame.part.5+0x79 (vmlinux)
uname 19058 506778.424430: 2457397 cycles: ffffffffa3019232 check_memory_region+0x52 (vmlinux)

Committer testing:

# rm -rf perf.data*
# perf record sleep 1
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.024 MB perf.data (7 samples) ]
# ls -l perf.data
-rw-------. 1 root root 34772 Oct 21 11:08 perf.data
# perf record --kcore uname
Linux
[ perf record: Woken up 1 times to write data ]
[ perf record: Captured and wrote 0.024 MB perf.data (7 samples) ]
ls[root@quaco ~]# ls -lad perf.data*
drwx------. 3 root root 4096 Oct 21 11:08 perf.data
-rw-------. 1 root root 34772 Oct 21 11:08 perf.data.old
# perf evlist -v
cycles: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
# perf evlist -v -i perf.data/data
cycles: size: 112, { sample_period, sample_freq }: 4000, sample_type: IP|TID|TIME|PERIOD, read_format: ID, disabled: 1, inherit: 1, mmap: 1, comm: 1, freq: 1, enable_on_exec: 1, task: 1, precise_ip: 3, sample_id_all: 1, exclude_guest: 1, mmap2: 1, comm_exec: 1, ksymbol: 1, bpf_event: 1
#

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Link: http://lore.kernel.org/lkml/20191004083121.12182-6-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

perf data: Support single perf.data file directory

Support directory output that contains a regular perf.data file, named
"data". By default the directory is named perf.data i.e.
perf.data
└── data

Most of the infrastructure to support a directory is already there. This
patch makes the changes needed to support the format above.

Presently there is no 'perf record' option to output a directory.

This is preparation for adding support for putting a copy of /proc/kcore in
the directory.

Signed-off-by: Adrian Hunter <adrian.hunter@intel.com>
Reviewed-by: Jiri Olsa <jolsa@kernel.org>
Link: http://lore.kernel.org/lkml/20191004083121.12182-5-adrian.hunter@intel.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>