logd: add getEventTag command and service

Will register a new event tag by name and format, and return an
event-log-tags format response with the newly allocated tag.
If format is not specified, then nothing will be recorded, but
a pre-existing named entry will be listed. If name and format are
not specified, list all dynamic entries. If name=* list all
event log tag entries.

Stickiness through logd crash will be managed with the tmpfs file
/dev/event-log-tags and through a reboot with add_tag entries in
the pmsg last logcat event log. On debug builds we retain a
/data/misc/logd/event-log-tags file that aids stickiness and that
can be picked up by the bugreport.

If we detect truncation damage to /dev/event-log-tags, or to
/data/misc/logd/event-log-tags, rebuild file with a new first line
signature incorporating the time so mmap'd readers of the file can
detect the possible change in shape and order.

Manual testing:

Make sure nc (netcat) is built for the target platform on the host:
$ m nc

Then the following can be used to issue a request on the platform:
$ echo -n 'getEventTag name=<name> format="<format>"\0EXIT\0' |
> nc -U /dev/socket/logd

Test: gTest logd-unit-test --gtest_filter=getEventTag*
Bug: 31456426
Change-Id: I5dacc5f84a24d52dae09cca5ee1a3a9f9207f06d

1 files changed, 3 insertions, 2 deletions

diff --git a/logd/LogUtils.h b/logd/LogUtils.h
index 70f24e4d9..f044b2744 100644
--- a/logd/LogUtils.h
+++ b/logd/LogUtils.h
@@ -39,8 +39,9 @@ size_t sizesTotal();
 char *pidToName(pid_t pid);
 char *tidToName(pid_t tid);
 
-// Furnished in main.cpp. Thread safe.
-const char *tagToName(size_t *len, uint32_t tag);
+// Furnished in LogTags.cpp. Thread safe.
+const char *tagToName(uint32_t tag);
+void ReReadEventLogTags();
 
 // Furnished by LogKlog.cpp.
 const char* strnstr(const char* s, size_t len, const char* needle);