trace2/tr2_sid.c

   1 #include "git-compat-util.h"
   2 #include "hex.h"
   3 #include "strbuf.h"
   4 #include "trace2/tr2_tbuf.h"
   5 #include "trace2/tr2_sid.h"
   6
   7 #define TR2_ENVVAR_PARENT_SID "GIT_TRACE2_PARENT_SID"
   8
   9 static struct strbuf tr2sid_buf = STRBUF_INIT;
  10 static int tr2sid_nr_git_parents;
  11
  12 /*
  13  * Compute the final component of the SID representing the current process.
  14  * This should uniquely identify the process and be a valid filename (to
  15  * allow writing trace2 data to per-process files).  It should also be fixed
  16  * length for possible use as a database key.
  17  *
  18  * "<yyyymmdd>T<hhmmss>.<fraction>Z-<host>-<process>"
  19  *
  20  * where <host> is a 9 character string:
  21  *    "H<first_8_chars_of_sha1_of_hostname>"
  22  *    "Localhost" when no hostname.
  23  *
  24  * where <process> is a 9 character string containing the least significant
  25  * 32 bits in the process-id.
  26  *    "P<pid>"
  27  * (This is an abribrary choice.  On most systems pid_t is a 32 bit value,
  28  * so limit doesn't matter.  On larger systems, a truncated value is fine
  29  * for our purposes here.)
  30  */
  31 static void tr2_sid_append_my_sid_component(void)
  32 {
  33         const struct git_hash_algo *algo = &hash_algos[GIT_HASH_SHA1];
  34         struct tr2_tbuf tb_now;
  35         git_hash_ctx ctx;
  36         pid_t pid = getpid();
  37         unsigned char hash[GIT_MAX_RAWSZ + 1];
  38         char hex[GIT_MAX_HEXSZ + 1];
  39         char hostname[HOST_NAME_MAX + 1];
  40
  41         tr2_tbuf_utc_datetime(&tb_now);
  42         strbuf_addstr(&tr2sid_buf, tb_now.buf);
  43
  44         strbuf_addch(&tr2sid_buf, '-');
  45         if (xgethostname(hostname, sizeof(hostname)))
  46                 strbuf_add(&tr2sid_buf, "Localhost", 9);
  47         else {
  48                 algo->init_fn(&ctx);
  49                 algo->update_fn(&ctx, hostname, strlen(hostname));
  50                 algo->final_fn(hash, &ctx);
  51                 hash_to_hex_algop_r(hex, hash, algo);
  52                 strbuf_addch(&tr2sid_buf, 'H');
  53                 strbuf_add(&tr2sid_buf, hex, 8);
  54         }
  55
  56         strbuf_addf(&tr2sid_buf, "-P%08"PRIx32, (uint32_t)pid);
  57 }
  58
  59 /*
  60  * Compute a "unique" session id (SID) for the current process.  This allows
  61  * all events from this process to have a single label (much like a PID).
  62  *
  63  * Export this into our environment so that all child processes inherit it.
  64  *
  65  * If we were started by another git instance, use our parent's SID as a
  66  * prefix.  (This lets us track parent/child relationships even if there
  67  * is an intermediate shell process.)
  68  *
  69  * Additionally, count the number of nested git processes.
  70  */
  71 static void tr2_sid_compute(void)
  72 {
  73         const char *parent_sid;
  74
  75         if (tr2sid_buf.len)
  76                 return;
  77
  78         parent_sid = getenv(TR2_ENVVAR_PARENT_SID);
  79         if (parent_sid && *parent_sid) {
  80                 const char *p;
  81                 for (p = parent_sid; *p; p++)
  82                         if (*p == '/')
  83                                 tr2sid_nr_git_parents++;
  84
  85                 strbuf_addstr(&tr2sid_buf, parent_sid);
  86                 strbuf_addch(&tr2sid_buf, '/');
  87                 tr2sid_nr_git_parents++;
  88         }
  89
  90         tr2_sid_append_my_sid_component();
  91
  92         setenv(TR2_ENVVAR_PARENT_SID, tr2sid_buf.buf, 1);
  93 }
  94
  95 const char *tr2_sid_get(void)
  96 {
  97         if (!tr2sid_buf.len)
  98                 tr2_sid_compute();
  99
 100         return tr2sid_buf.buf;
 101 }
 102
 103 int tr2_sid_depth(void)
 104 {
 105         if (!tr2sid_buf.len)
 106                 tr2_sid_compute();
 107
 108         return tr2sid_nr_git_parents;
 109 }
 110
 111 void tr2_sid_release(void)
 112 {
 113         strbuf_release(&tr2sid_buf);
 114 }