[tip:perf/core] tools lib bpf: Use FEATURE_USER to allow building in the same dir as perf

[tip-bot for Arnaldo Carvalho de Melo]

Commit-ID:  65f041bee7838e2a91dbbc0a917d9291adbb3484
Gitweb:     http://git.kernel.org/tip/65f041bee7838e2a91dbbc0a917d9291adbb3484
Author:     Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
AuthorDate: Mon, 21 Sep 2015 17:25:27 -0300
Committer:  Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
CommitDate: Tue, 22 Sep 2015 10:47:05 -0300

tools lib bpf: Use FEATURE_USER to allow building in the same dir as perf

When building tools/lib/bpf as part of the tools/perf/ build process,
which will happend when we introduce a patch wiring that up, we end up
stomping on the feature detection caching mechanism, that uses a file in
the output directory (O=) that is shared by libbpf and perf to check if
something changed from one build to another that requires redoing the
feature detection process.

By using the recently introduced FEATURE_USER tools/build/ knob, we can
avoid that:

Before, every make invokation would run the feature detection:

  $ make O=/tmp/build/perf -C tools/perf
  make: Entering directory '/home/git/linux/tools/perf'
  Auto-detecting system features:
  ...                         dwarf: [ on  ]
  ...                         glibc: [ on  ]
  <SNIP>
  ...                     get_cpuid: [ on  ]
  ...                           bpf: [ on  ]

    GEN      perf-archive
    GEN      perf-with-kcore

  Auto-detecting system features:
  ...                        libelf: [ on  ]
  ...                           bpf: [ on  ]
  <SNIP>

After:

  $ make O=/tmp/build/perf -C tools/perf
  make: Entering directory '/home/git/linux/tools/perf'
    BUILD:   Doing 'make -j4' parallel build
  make: Leaving directory '/home/git/linux/tools/perf'
  $

Because we now have two different feature detection state files:

  $ ls -la /tmp/build/perf/FEATURE-DUMP*
  -rw-rw-r--. 1 acme acme 338 Sep 21 17:25 /tmp/build/perf/FEATURE-DUMP
  -rw-rw-r--. 1 acme acme  33 Sep 21 17:25 /tmp/build/perf/FEATURE-DUMP.libbpf
  $

Acked-by: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Adrian Hunter <adrian.hunter@xxxxxxxxx>
Cc: Alexei Starovoitov <ast@xxxxxxxxxxxx>
Cc: Borislav Petkov <bp@xxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Stephane Eranian <eranian@xxxxxxxxxx>
Cc: Wang Nan <wangnan0@xxxxxxxxxx>
Cc: pi3orama@xxxxxxx
Fixes: 1b76c13e4b36 ("bpf tools: Introduce 'bpf' library and add bpf feature check")
Link: http://lkml.kernel.org/n/tip-s6ev9wfqy7pvvs58emys2g90@xxxxxxxxxxxxxx
Signed-off-by: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
---
 tools/lib/bpf/Makefile | 1 +
 1 file changed, 1 insertion(+)

diff --git a/tools/lib/bpf/Makefile b/tools/lib/bpf/Makefile
index 604c120..e630f9f 100644
--- a/tools/lib/bpf/Makefile
+++ b/tools/lib/bpf/Makefile
@@ -64,6 +64,7 @@ srctree := $(patsubst %/,%,$(dir $(srctree)))
 #$(info Determined 'srctree' to be $(srctree))
 endif
 
+FEATURE_USER = .libbpf
 FEATURE_TESTS = libelf libelf-getphdrnum libelf-mmap bpf
 FEATURE_DISPLAY = libelf bpf
 
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