git

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#include "git-compat-util.h"
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#include "hex.h"
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#include "strbuf.h"
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#include "trace2/tr2_tbuf.h"
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#include "trace2/tr2_sid.h"
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#define TR2_ENVVAR_PARENT_SID "GIT_TRACE2_PARENT_SID"
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static struct strbuf tr2sid_buf = STRBUF_INIT;
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static int tr2sid_nr_git_parents;
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/*
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 * Compute the final component of the SID representing the current process.
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 * This should uniquely identify the process and be a valid filename (to
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 * allow writing trace2 data to per-process files).  It should also be fixed
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 * length for possible use as a database key.
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 *
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 * "<yyyymmdd>T<hhmmss>.<fraction>Z-<host>-<process>"
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 *
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 * where <host> is a 9 character string:
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 *    "H<first_8_chars_of_sha1_of_hostname>"
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 *    "Localhost" when no hostname.
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 *
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 * where <process> is a 9 character string containing the least significant
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 * 32 bits in the process-id.
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 *    "P<pid>"
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 * (This is an abribrary choice.  On most systems pid_t is a 32 bit value,
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 * so limit doesn't matter.  On larger systems, a truncated value is fine
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 * for our purposes here.)
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 */
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static void tr2_sid_append_my_sid_component(void)
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{
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	const struct git_hash_algo *algo = &hash_algos[GIT_HASH_SHA1];
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	struct tr2_tbuf tb_now;
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	git_hash_ctx ctx;
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	pid_t pid = getpid();
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	unsigned char hash[GIT_MAX_RAWSZ + 1];
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	char hex[GIT_MAX_HEXSZ + 1];
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	char hostname[HOST_NAME_MAX + 1];
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	tr2_tbuf_utc_datetime(&tb_now);
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	strbuf_addstr(&tr2sid_buf, tb_now.buf);
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	strbuf_addch(&tr2sid_buf, '-');
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	if (xgethostname(hostname, sizeof(hostname)))
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		strbuf_add(&tr2sid_buf, "Localhost", 9);
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	else {
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		algo->init_fn(&ctx);
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		algo->update_fn(&ctx, hostname, strlen(hostname));
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		algo->final_fn(hash, &ctx);
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		hash_to_hex_algop_r(hex, hash, algo);
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		strbuf_addch(&tr2sid_buf, 'H');
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		strbuf_add(&tr2sid_buf, hex, 8);
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	}
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	strbuf_addf(&tr2sid_buf, "-P%08"PRIx32, (uint32_t)pid);
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}
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/*
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 * Compute a "unique" session id (SID) for the current process.  This allows
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 * all events from this process to have a single label (much like a PID).
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 *
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 * Export this into our environment so that all child processes inherit it.
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 *
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 * If we were started by another git instance, use our parent's SID as a
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 * prefix.  (This lets us track parent/child relationships even if there
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 * is an intermediate shell process.)
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 *
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 * Additionally, count the number of nested git processes.
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 */
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static void tr2_sid_compute(void)
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{
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	const char *parent_sid;
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	if (tr2sid_buf.len)
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		return;
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	parent_sid = getenv(TR2_ENVVAR_PARENT_SID);
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	if (parent_sid && *parent_sid) {
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		const char *p;
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		for (p = parent_sid; *p; p++)
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			if (*p == '/')
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				tr2sid_nr_git_parents++;
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		strbuf_addstr(&tr2sid_buf, parent_sid);
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		strbuf_addch(&tr2sid_buf, '/');
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		tr2sid_nr_git_parents++;
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	}
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	tr2_sid_append_my_sid_component();
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	setenv(TR2_ENVVAR_PARENT_SID, tr2sid_buf.buf, 1);
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}
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const char *tr2_sid_get(void)
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{
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	if (!tr2sid_buf.len)
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		tr2_sid_compute();
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	return tr2sid_buf.buf;
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}
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int tr2_sid_depth(void)
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{
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	if (!tr2sid_buf.len)
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		tr2_sid_compute();
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	return tr2sid_nr_git_parents;
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}
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void tr2_sid_release(void)
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{
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	strbuf_release(&tr2sid_buf);
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}
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