path: root/tools/perf/design.txt
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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2009-06-12 12:46:55 +0200
committerIngo Molnar <mingo@elte.hu>2009-06-12 14:28:52 +0200
commit974802eaa1afdc87e00821df7020a2b3c6fee623 (patch)
treeb5c38bece7f4948fe9d5cf9be02a0042e0fa39f6 /tools/perf/design.txt
parentbbd36e5e6aa6f1757c84cdb406b6eb81686d14af (diff)
perf_counter: Add forward/backward attribute ABI compatibility
Provide for means of extending the perf_counter_attr in a 'natural' way. We allow growing the structure by appending fields at the end by specifying the full structure size inside it. When a new kernel sees a smaller (old) structure, it will 0 pad the tail. When an old kernel sees a larger (new) structure, it will verify the tail consists of 0s, otherwise fail. If we fail due to a size-mismatch, we return -E2BIG and write the kernel's native attribe size back into the provided structure. Furthermore, add some attribute verification, so that we'll fail counter creation when unknown bits are present (PERF_SAMPLE, PERF_FORMAT, or in the __reserved fields). (This ABI detail is introduced while keeping the existing syscall ABI.) Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: Mike Galbraith <efault@gmx.de> Cc: Paul Mackerras <paulus@samba.org> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
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