With 'perf script' it is common that we just want to add or remove a field.

Currently this requires figuring out the long list of default fields and
specifying them first, and then adding/removing the new field.

This patch adds a new + - syntax to merely add or remove fields,
that allows more succint and clearer command lines

For example to remove the comm field from PMU samples:

Previously

  $ perf script -F tid,cpu,time,event,sym,ip,dso,period | head -1
  swapper  0 [000] 504345.383126:          1 cycles:  ffffffff90060c66 native_write_msr ([kernel.kallsyms])

with the new syntax

  perf script -F -comm | head -1
  0 [000] 504345.383126:          1 cycles:  ffffffff90060c66 native_write_msr ([kernel.kallsyms])

The new syntax cannot be mixed with normal overriding.

v2: Fix example in description. Use tid vs pid. No functional changes.
v3: Don't skip initialization when user specified explicit type.
v4: Rebase. Remove empty line.

Committer testing:

  # perf record -a usleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 1.748 MB perf.data (14 samples) ]

Without a explicit field list specified via -F, defaults to:

  # perf script | head -2
      perf 6338 [000] 18467.058607: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
   swapper    0 [001] 18467.058617: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
  #

Which is equivalent to:

  # perf script -F comm,tid,cpu,time,period,event,ip,sym,dso | head -2
      perf 6338 [000] 18467.058607: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
   swapper    0 [001] 18467.058617: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
  #

So if we want to remove the comm, as in your original example, we would have to
figure out the default field list and remove ' comm' from it:

  # perf script -F tid,cpu,time,period,event,ip,sym,dso | head -2
   6338 [000] 18467.058607: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
      0 [001] 18467.058617: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
  #

With your patch this becomes simpler, one can remove fields by prefixing them
with '-':

  # perf script -F -comm | head -2
  6338 [000] 18467.058607: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
     0 [001] 18467.058617: 1 cycles: ffffffff89060c36 native_write_msr (/lib/modules/4.11.0-rc8+/build/vmlinux)
  #
Signed-off-by: Andi Kleen <ak@linux.intel.com>
Acked-by: Jiri Olsa <jolsa@kernel.org>
Tested-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Tested-by: Milian Wolff <milian.wolff@kdab.com>
Link: http://lkml.kernel.org/r/20170602154810.15875-1-andi@firstfloor.orgSigned-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>