Missing information in HEADER_CPU_DOMAIN_INFO

[Thomas Richter <tmricht@linux.ibm.com>]

Hi Swapnil,

Commit d40c68a49f69 ("perf header: Support CPU DOMAIN relation info")
introduced the HEADER_CPU_DOMAIN_INFO bit and the necessary data.

However two issues came to my attention.

1. The documentation is incomplete.
File Documentation/perf.data-file-format.txt differs from the data written
in function write_cpu_domain_info().
The first two values written to the header section are schedstat_version
and max_sched_domains. They are missing in the documentation.

2. The function write_cpu_domain_info() writes a variable amount of data,
but does not indicate how much CPU members have actually been written.
This makes it much harder to read back that data from a perf.data file,
because the reader does not know in advance how much data to read.
Since the data structures also contain strings, the file section size does
not help at all, because strings are of variable size.

In my opinion the structure should contain the number of CPU data to read.
My suggestion:
Modify structure cpu_domain_info, which contains the
missing schedstat_version and max_sched_domains fields and contains the
number of CPU records actually written to that header section.
Here is an idea:

        HEADER_CPU_DOMAIN_INFO = 32,

 List of cpu-domain relation info. The format of the data is as below.

 struct domain_info {
        int domain;
        char dname[];
        char cpumask[];
        char cpulist[];
 };

 struct cpu_domain_info {
        int schedstat_version;
        int max_sched_domains;
        int nr_cpus;             <--- new
        struct {
                u32 cpu;
                u32 nr_domains;
                struct domain_info [nr_domains];
        } [nr_cpus];
 };

The above syntax is also in sync the other sections of that documentation file.

What do you think?

-- 
Thomas Richter, Dept 3303, IBM s390 Linux Development, Boeblingen, Germany
--
IBM Deutschland Research & Development GmbH

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