trace2/tr2_sid.c

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