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trace2: make SIDs more unique

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Update SID component construction to use the current UTC datetime
and a portion of the SHA1 of the hostname.

Use an simplified date/time format to make it easier to use the
SID component as a logfile filename.

Signed-off-by: Jeff Hostetler <jeffhost@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Jeff Hostetler
2019-04-15 13:39:49 -07:00
committed by Junio C Hamano
parent bad229aef2
commit 08881b9a4c
4 changed files with 73 additions and 12 deletions
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53
trace2/tr2_sid.c
View File

@@ -1,4 +1,5 @@
#include "cache.h"
#include "trace2/tr2_tbuf.h"
#include "trace2/tr2_sid.h"
#define TR2_ENVVAR_PARENT_SID "GIT_TR2_PARENT_SID"
@@ -6,6 +7,53 @@
static struct strbuf tr2sid_buf = STRBUF_INIT;
static int tr2sid_nr_git_parents;
/*
* Compute the final component of the SID representing the current process.
* This should uniquely identify the process and be a valid filename (to
* allow writing trace2 data to per-process files). It should also be fixed
* length for possible use as a database key.
*
* "<yyyymmdd>T<hhmmss>.<fraction>Z-<host>-<process>"
*
* where <host> is a 9 character string:
* "H<first_8_chars_of_sha1_of_hostname>"
* "Localhost" when no hostname.
*
* where <process> is a 9 character string containing the least signifcant
* 32 bits in the process-id.
* "P<pid>"
* (This is an abribrary choice. On most systems pid_t is a 32 bit value,
* so limit doesn't matter. On larger systems, a truncated value is fine
* for our purposes here.)
*/
static void tr2_sid_append_my_sid_component(void)
{
const struct git_hash_algo *algo = &hash_algos[GIT_HASH_SHA1];
struct tr2_tbuf tb_now;
git_hash_ctx ctx;
pid_t pid = getpid();
unsigned char hash[GIT_MAX_RAWSZ + 1];
char hex[GIT_MAX_HEXSZ + 1];
char hostname[HOST_NAME_MAX + 1];
tr2_tbuf_utc_datetime(&tb_now);
strbuf_addstr(&tr2sid_buf, tb_now.buf);
strbuf_addch(&tr2sid_buf, '-');
if (xgethostname(hostname, sizeof(hostname)))
strbuf_add(&tr2sid_buf, "Localhost", 9);
else {
algo->init_fn(&ctx);
algo->update_fn(&ctx, hostname, strlen(hostname));
algo->final_fn(hash, &ctx);
hash_to_hex_algop_r(hex, hash, algo);
strbuf_addch(&tr2sid_buf, 'H');
strbuf_add(&tr2sid_buf, hex, 8);
}
strbuf_addf(&tr2sid_buf, "-P%08"PRIx32, (uint32_t)pid);
}
/*
* Compute a "unique" session id (SID) for the current process. This allows
* all events from this process to have a single label (much like a PID).
@@ -20,7 +68,6 @@ static int tr2sid_nr_git_parents;
*/
static void tr2_sid_compute(void)
{
uint64_t us_now;
const char *parent_sid;
if (tr2sid_buf.len)
@@ -38,9 +85,7 @@ static void tr2_sid_compute(void)
tr2sid_nr_git_parents++;
}
us_now = getnanotime() / 1000;
strbuf_addf(&tr2sid_buf, "%" PRIuMAX "-%" PRIdMAX, (uintmax_t)us_now,
(intmax_t)getpid());
tr2_sid_append_my_sid_component();
setenv(TR2_ENVVAR_PARENT_SID, tr2sid_buf.buf, 1);
}