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+perf.data directory format
+
+DISCLAIMER This is not ABI yet and is subject to possible change
+           in following versions of perf. We will remove this
+           disclaimer once the directory format soaks in.
+
+
+This document describes the on-disk perf.data directory format.
+
+The layout is described by HEADER_DIR_FORMAT feature.
+Currently it holds only version number (0):
+
+  HEADER_DIR_FORMAT = 24
+
+  struct {
+     uint64_t version;
+  }
+
+The current only version value 0 means that:
+  - there is a single perf.data file named 'data' within the directory.
+  e.g.
+
+    $ tree -ps perf.data
+    perf.data
+    └── [-rw-------       25912]  data
+
+Future versions are expected to describe different data files
+layout according to special needs.
+
+Currently the only 'perf record' option to output to a directory is
+the --kcore option which puts a copy of /proc/kcore into the directory.
+e.g.
+
+  $ sudo perf record --kcore uname
+  Linux
+  [ perf record: Woken up 1 times to write data ]
+  [ perf record: Captured and wrote 0.015 MB perf.data (9 samples) ]
+  $ sudo tree -ps perf.data
+  perf.data
+  ├── [-rw-------       23744]  data
+  └── [drwx------        4096]  kcore_dir
+      ├── [-r--------     6731125]  kallsyms
+      ├── [-r--------    40230912]  kcore
+      └── [-r--------        5419]  modules
+
+  1 directory, 4 files
+  $ sudo perf script -v
+  build id event received for vmlinux: 1eaa285996affce2d74d8e66dcea09a80c9941de
+  build id event received for [vdso]: 8bbaf5dc62a9b644b4d4e4539737e104e4a84541
+  build id event received for /lib/x86_64-linux-gnu/libc-2.28.so: 5b157f49586a3ca84d55837f97ff466767dd3445
+  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 15316 2060795.480902:          1 cycles:  ffffffffa2caa548 native_write_msr+0x8 (vmlinux)
+              perf 15316 2060795.480906:          1 cycles:  ffffffffa2caa548 native_write_msr+0x8 (vmlinux)
+              perf 15316 2060795.480908:          7 cycles:  ffffffffa2caa548 native_write_msr+0x8 (vmlinux)
+              perf 15316 2060795.480910:        119 cycles:  ffffffffa2caa54a native_write_msr+0xa (vmlinux)
+              perf 15316 2060795.480912:       2109 cycles:  ffffffffa2c9b7b0 native_apic_msr_write+0x0 (vmlinux)
+              perf 15316 2060795.480914:      37606 cycles:  ffffffffa2f121fe perf_event_addr_filters_exec+0x2e (vmlinux)
+             uname 15316 2060795.480924:     588287 cycles:  ffffffffa303a56d page_counter_try_charge+0x6d (vmlinux)
+             uname 15316 2060795.481067:    2261945 cycles:  ffffffffa301438f kmem_cache_free+0x4f (vmlinux)
+             uname 15316 2060795.481643:    2172167 cycles:      7f1a48c393c0 _IO_un_link+0x0 (/lib/x86_64-linux-gnu/libc-2.28.so)