#define USE_THE_REPOSITORY_VARIABLE

#include "git-compat-util.h"

#include "config.h"

#include "dir.h"

#include "environment.h"

#include "ewah/ewok.h"

#include "fsmonitor.h"

#include "fsmonitor-ipc.h"

#include "name-hash.h"

#include "run-command.h"

#include "strbuf.h"

#include "trace2.h"

#define INDEX_EXTENSION_VERSION1  (1)

#define INDEX_EXTENSION_VERSION2  (2)

#define HOOK_INTERFACE_VERSION1   (1)

#define HOOK_INTERFACE_VERSION2   (2)

struct trace_key trace_fsmonitor = TRACE_KEY_INIT(FSMONITOR);

static void assert_index_minimum(struct index_state *istate, size_t pos)

{

  if (pos > istate->cache_nr)

    BUG("fsmonitor_dirty has more entries than the index (%"PRIuMAX" > %u)",

        (uintmax_t)pos, istate->cache_nr);

}

static void fsmonitor_ewah_callback(size_t pos, void *is)

{

  struct index_state *istate = (struct index_state *)is;

  struct cache_entry *ce;

  assert_index_minimum(istate, pos + 1);

  ce = istate->cache[pos];

  ce->ce_flags &= ~CE_FSMONITOR_VALID;

}

static int fsmonitor_hook_version(void)

{

  int hook_version;

  if (git_config_get_int("core.fsmonitorhookversion", &hook_version))

    return -1;

  if (hook_version == HOOK_INTERFACE_VERSION1 ||

      hook_version == HOOK_INTERFACE_VERSION2)

    return hook_version;

  warning("Invalid hook version '%i' in core.fsmonitorhookversion. "

    "Must be 1 or 2.", hook_version);

  return -1;

}

int read_fsmonitor_extension(struct index_state *istate, const void *data,

  unsigned long sz)

{

  const char *index = data;

  uint32_t hdr_version;

  uint32_t ewah_size;

  struct ewah_bitmap *fsmonitor_dirty;

  int ret;

  uint64_t timestamp;

  struct strbuf last_update = STRBUF_INIT;

  if (sz < sizeof(uint32_t) + 1 + sizeof(uint32_t))

    return error("corrupt fsmonitor extension (too short)");

  hdr_version = get_be32(index);

  index += sizeof(uint32_t);

  if (hdr_version == INDEX_EXTENSION_VERSION1) {

    timestamp = get_be64(index);

    strbuf_addf(&last_update, "%"PRIu64"", timestamp);

    index += sizeof(uint64_t);

  } else if (hdr_version == INDEX_EXTENSION_VERSION2) {

    strbuf_addstr(&last_update, index);

    index += last_update.len + 1;

  } else {

    return error("bad fsmonitor version %d", hdr_version);

  }

  istate->fsmonitor_last_update = strbuf_detach(&last_update, NULL);

  ewah_size = get_be32(index);

  index += sizeof(uint32_t);

  fsmonitor_dirty = ewah_new();

  ret = ewah_read_mmap(fsmonitor_dirty, index, ewah_size);

  if (ret != ewah_size) {

    ewah_free(fsmonitor_dirty);

    return error("failed to parse ewah bitmap reading fsmonitor index extension");

  }

  istate->fsmonitor_dirty = fsmonitor_dirty;

  if (!istate->split_index)

    assert_index_minimum(istate, istate->fsmonitor_dirty->bit_size);

  trace2_data_string("index", NULL, "extension/fsmn/read/token",

         istate->fsmonitor_last_update);

  trace_printf_key(&trace_fsmonitor,

       "read fsmonitor extension successful '%s'",

       istate->fsmonitor_last_update);

  return 0;

}

void fill_fsmonitor_bitmap(struct index_state *istate)

{

  unsigned int i, skipped = 0;

  istate->fsmonitor_dirty = ewah_new();

  for (i = 0; i < istate->cache_nr; i++) {

    if (istate->cache[i]->ce_flags & CE_REMOVE)

      skipped++;

    else if (!(istate->cache[i]->ce_flags & CE_FSMONITOR_VALID))

      ewah_set(istate->fsmonitor_dirty, i - skipped);

  }

}

void write_fsmonitor_extension(struct strbuf *sb, struct index_state *istate)

{

  uint32_t hdr_version;

  uint32_t ewah_start;

  uint32_t ewah_size = 0;

  int fixup = 0;

  if (!istate->split_index)

    assert_index_minimum(istate, istate->fsmonitor_dirty->bit_size);

  put_be32(&hdr_version, INDEX_EXTENSION_VERSION2);

  strbuf_add(sb, &hdr_version, sizeof(uint32_t));

  strbuf_addstr(sb, istate->fsmonitor_last_update);

  strbuf_addch(sb, 0); /* Want to keep a NUL */

  fixup = sb->len;

  strbuf_add(sb, &ewah_size, sizeof(uint32_t)); /* we'll fix this up later */

  ewah_start = sb->len;

  ewah_serialize_strbuf(istate->fsmonitor_dirty, sb);

  ewah_free(istate->fsmonitor_dirty);

  istate->fsmonitor_dirty = NULL;

  /* fix up size field */

  put_be32(&ewah_size, sb->len - ewah_start);

  memcpy(sb->buf + fixup, &ewah_size, sizeof(uint32_t));

  trace2_data_string("index", NULL, "extension/fsmn/write/token",

         istate->fsmonitor_last_update);

  trace_printf_key(&trace_fsmonitor,

       "write fsmonitor extension successful '%s'",

       istate->fsmonitor_last_update);

}

/*

 * Call the query-fsmonitor hook passing the last update token of the saved results.

 */

static int query_fsmonitor_hook(struct repository *r,

        int version,

        const char *last_update,

        struct strbuf *query_result)

{

  struct child_process cp = CHILD_PROCESS_INIT;

  int result;

  if (fsm_settings__get_mode(r) != FSMONITOR_MODE_HOOK)

    return -1;

  strvec_push(&cp.args, fsm_settings__get_hook_path(r));

  strvec_pushf(&cp.args, "%d", version);

  strvec_pushf(&cp.args, "%s", last_update);

  cp.use_shell = 1;

  cp.dir = get_git_work_tree();

  trace2_region_enter("fsm_hook", "query", NULL);

  result = capture_command(&cp, query_result, 1024);

  if (result)

    trace2_data_intmax("fsm_hook", NULL, "query/failed", result);

  else

    trace2_data_intmax("fsm_hook", NULL, "query/response-length",

           query_result->len);

  trace2_region_leave("fsm_hook", "query", NULL);

  return result;

}

/*

 * Invalidate the FSM bit on this CE.  This is like mark_fsmonitor_invalid()

 * but we've already handled the untracked-cache, so let's not repeat that

 * work.  This also lets us have a different trace message so that we can

 * see everything that was done as part of the refresh-callback.

 */

static void invalidate_ce_fsm(struct cache_entry *ce)

{

  if (ce->ce_flags & CE_FSMONITOR_VALID) {

    trace_printf_key(&trace_fsmonitor,

         "fsmonitor_refresh_callback INV: '%s'",

         ce->name);

    ce->ce_flags &= ~CE_FSMONITOR_VALID;

  }

}

static size_t handle_path_with_trailing_slash(

  struct index_state *istate, const char *name, int pos);

/*

 * Use the name-hash to do a case-insensitive cache-entry lookup with

 * the pathname and invalidate the cache-entry.

 *

 * Returns the number of cache-entries that we invalidated.

 */

static size_t handle_using_name_hash_icase(

  struct index_state *istate, const char *name)

{

  struct cache_entry *ce = NULL;

  ce = index_file_exists(istate, name, strlen(name), 1);

  if (!ce)

    return 0;

  /*

   * A case-insensitive search in the name-hash using the

   * observed pathname found a cache-entry, so the observed path

   * is case-incorrect.  Invalidate the cache-entry and use the

   * correct spelling from the cache-entry to invalidate the

   * untracked-cache.  Since we now have sparse-directories in

   * the index, the observed pathname may represent a regular

   * file or a sparse-index directory.

   *

   * Note that we should not have seen FSEvents for a

   * sparse-index directory, but we handle it just in case.

   *

   * Either way, we know that there are not any cache-entries for

   * children inside the cone of the directory, so we don't need to

   * do the usual scan.

   */

  trace_printf_key(&trace_fsmonitor,

       "fsmonitor_refresh_callback MAP: '%s' '%s'",

       name, ce->name);

  /*

   * NEEDSWORK: We used the name-hash to find the correct

   * case-spelling of the pathname in the cache-entry[], so

   * technically this is a tracked file or a sparse-directory.

   * It should not have any entries in the untracked-cache, so

   * we should not need to use the case-corrected spelling to

   * invalidate the the untracked-cache.  So we may not need to

   * do this.  For now, I'm going to be conservative and always

   * do it; we can revisit this later.

   */

  untracked_cache_invalidate_trimmed_path(istate, ce->name, 0);

  invalidate_ce_fsm(ce);

  return 1;

}

/*

 * Use the dir-name-hash to find the correct-case spelling of the

 * directory.  Use the canonical spelling to invalidate all of the

 * cache-entries within the matching cone.

 *

 * Returns the number of cache-entries that we invalidated.

 */

static size_t handle_using_dir_name_hash_icase(

  struct index_state *istate, const char *name)

{

  struct strbuf canonical_path = STRBUF_INIT;

  int pos;

  size_t len = strlen(name);

  size_t nr_in_cone;

  if (name[len - 1] == '/')

    len--;

  if (!index_dir_find(istate, name, len, &canonical_path))

    return 0; /* name is untracked */

  if (!memcmp(name, canonical_path.buf, canonical_path.len)) {

    strbuf_release(&canonical_path);

    /*

     * NEEDSWORK: Our caller already tried an exact match

     * and failed to find one.  They called us to do an

     * ICASE match, so we should never get an exact match,

     * so we could promote this to a BUG() here if we

     * wanted to.  It doesn't hurt anything to just return

     * 0 and go on because we should never get here.  Or we

     * could just get rid of the memcmp() and this "if"

     * clause completely.

     */

    BUG("handle_using_dir_name_hash_icase(%s) did not exact match",

        name);

  }

  trace_printf_key(&trace_fsmonitor,

       "fsmonitor_refresh_callback MAP: '%s' '%s'",

       name, canonical_path.buf);

  /*

   * The dir-name-hash only tells us the corrected spelling of

   * the prefix.  We have to use this canonical path to do a

   * lookup in the cache-entry array so that we repeat the

   * original search using the case-corrected spelling.

   */

  strbuf_addch(&canonical_path, '/');

  pos = index_name_pos(istate, canonical_path.buf,

           canonical_path.len);

  nr_in_cone = handle_path_with_trailing_slash(

    istate, canonical_path.buf, pos);

  strbuf_release(&canonical_path);

  return nr_in_cone;

}

/*

 * The daemon sent an observed pathname without a trailing slash.

 * (This is the normal case.)  We do not know if it is a tracked or

 * untracked file, a sparse-directory, or a populated directory (on a

 * platform such as Windows where FSEvents are not qualified).

 *

 * The pathname contains the observed case reported by the FS. We

 * do not know it is case-correct or -incorrect.

 *

 * Assume it is case-correct and try an exact match.

 *

 * Return the number of cache-entries that we invalidated.

 */

static size_t handle_path_without_trailing_slash(

  struct index_state *istate, const char *name, int pos)

{

  /*

   * Mark the untracked cache dirty for this path (regardless of

   * whether or not we find an exact match for it in the index).

   * Since the path is unqualified (no trailing slash hint in the

   * FSEvent), it may refer to a file or directory. So we should

   * not assume one or the other and should always let the untracked

   * cache decide what needs to invalidated.

   */

  untracked_cache_invalidate_trimmed_path(istate, name, 0);

  if (pos >= 0) {

    /*

     * An exact match on a tracked file. We assume that we

     * do not need to scan forward for a sparse-directory

     * cache-entry with the same pathname, nor for a cone

     * at that directory. (That is, assume no D/F conflicts.)

     */

    invalidate_ce_fsm(istate->cache[pos]);

    return 1;

  } else {

    size_t nr_in_cone;

    struct strbuf work_path = STRBUF_INIT;

    /*

     * The negative "pos" gives us the suggested insertion

     * point for the pathname (without the trailing slash).

     * We need to see if there is a directory with that

     * prefix, but there can be lots of pathnames between

     * "foo" and "foo/" like "foo-" or "foo-bar", so we

     * don't want to do our own scan.

     */

    strbuf_add(&work_path, name, strlen(name));

    strbuf_addch(&work_path, '/');

    pos = index_name_pos(istate, work_path.buf, work_path.len);

    nr_in_cone = handle_path_with_trailing_slash(

      istate, work_path.buf, pos);

    strbuf_release(&work_path);

    return nr_in_cone;

  }

}

/*

 * The daemon can decorate directory events, such as a move or rename,

 * by adding a trailing slash to the observed name.  Use this to

 * explicitly invalidate the entire cone under that directory.

 *

 * The daemon can only reliably do that if the OS FSEvent contains

 * sufficient information in the event.

 *

 * macOS FSEvents have enough information.

 *

 * Other platforms may or may not be able to do it (and it might

 * depend on the type of event (for example, a daemon could lstat() an

 * observed pathname after a rename, but not after a delete)).

 *

 * If we find an exact match in the index for a path with a trailing

 * slash, it means that we matched a sparse-index directory in a

 * cone-mode sparse-checkout (since that's the only time we have

 * directories in the index).  We should never see this in practice

 * (because sparse directories should not be present and therefore

 * not generating FS events).  Either way, we can treat them in the

 * same way and just invalidate the cache-entry and the untracked

 * cache (and in this case, the forward cache-entry scan won't find

 * anything and it doesn't hurt to let it run).

 *

 * Return the number of cache-entries that we invalidated.  We will

 * use this later to determine if we need to attempt a second

 * case-insensitive search on case-insensitive file systems.  That is,

 * if the search using the observed-case in the FSEvent yields any

 * results, we assume the prefix is case-correct.  If there are no

 * matches, we still don't know if the observed path is simply

 * untracked or case-incorrect.

 */

static size_t handle_path_with_trailing_slash(

  struct index_state *istate, const char *name, int pos)

{

  int i;

  size_t nr_in_cone = 0;

  /*

   * Mark the untracked cache dirty for this directory path

   * (regardless of whether or not we find an exact match for it

   * in the index or find it to be proper prefix of one or more

   * files in the index), since the FSEvent is hinting that

   * there may be changes on or within the directory.

   */

  untracked_cache_invalidate_trimmed_path(istate, name, 0);

  if (pos < 0)

    pos = -pos - 1;

  /* Mark all entries for the folder invalid */

  for (i = pos; i < istate->cache_nr; i++) {

    if (!starts_with(istate->cache[i]->name, name))

      break;

    invalidate_ce_fsm(istate->cache[i]);

    nr_in_cone++;

  }

  return nr_in_cone;

}

static void fsmonitor_refresh_callback(struct index_state *istate, char *name)

{

  int len = strlen(name);

  int pos = index_name_pos(istate, name, len);

  size_t nr_in_cone;

  trace_printf_key(&trace_fsmonitor,

       "fsmonitor_refresh_callback '%s' (pos %d)",

       name, pos);

  if (name[len - 1] == '/')

    nr_in_cone = handle_path_with_trailing_slash(istate, name, pos);

  else

    nr_in_cone = handle_path_without_trailing_slash(istate, name, pos);

  /*

   * If we did not find an exact match for this pathname or any

   * cache-entries with this directory prefix and we're on a

   * case-insensitive file system, try again using the name-hash

   * and dir-name-hash.

   */

  if (!nr_in_cone && ignore_case) {

    nr_in_cone = handle_using_name_hash_icase(istate, name);

    if (!nr_in_cone)

      nr_in_cone = handle_using_dir_name_hash_icase(

        istate, name);

  }

  if (nr_in_cone)

    trace_printf_key(&trace_fsmonitor,

         "fsmonitor_refresh_callback CNT: %d",

         (int)nr_in_cone);

}

/*

 * The number of pathnames that we need to receive from FSMonitor

 * before we force the index to be updated.

 *

 * Note that any pathname within the set of received paths MAY cause

 * cache-entry or istate flag bits to be updated and thus cause the

 * index to be updated on disk.

 *

 * However, the response may contain many paths (such as ignored

 * paths) that will not update any flag bits.  And thus not force the

 * index to be updated.  (This is fine and normal.)  It also means

 * that the token will not be updated in the FSMonitor index

 * extension.  So the next Git command will find the same token in the

 * index, make the same token-relative request, and receive the same

 * response (plus any newly changed paths).  If this response is large

 * (and continues to grow), performance could be impacted.

 *

 * For example, if the user runs a build and it writes 100K object

 * files but doesn't modify any source files, the index would not need

 * to be updated.  The FSMonitor response (after the build and

 * relative to a pre-build token) might be 5MB.  Each subsequent Git

 * command will receive that same 100K/5MB response until something

 * causes the index to be updated.  And `refresh_fsmonitor()` will

 * have to iterate over those 100K paths each time.

 *

 * Performance could be improved if we optionally force update the

 * index after a very large response and get an updated token into

 * the FSMonitor index extension.  This should allow subsequent

 * commands to get smaller and more current responses.

 *

 * The value chosen here does not need to be precise.  The index

 * will be updated automatically the first time the user touches

 * a tracked file and causes a command like `git status` to

 * update an mtime to be updated and/or set a flag bit.

 */

static int fsmonitor_force_update_threshold = 100;

void refresh_fsmonitor(struct index_state *istate)

{

  static int warn_once = 0;

  struct strbuf query_result = STRBUF_INIT;

  int query_success = 0, hook_version = -1;

  size_t bol = 0; /* beginning of line */

  uint64_t last_update;

  struct strbuf last_update_token = STRBUF_INIT;

  char *buf;

  unsigned int i;

  int is_trivial = 0;

  struct repository *r = istate->repo;

  enum fsmonitor_mode fsm_mode = fsm_settings__get_mode(r);

  enum fsmonitor_reason reason = fsm_settings__get_reason(r);

  if (!warn_once && reason > FSMONITOR_REASON_OK) {

    char *msg = fsm_settings__get_incompatible_msg(r, reason);

    warn_once = 1;

    warning("%s", msg);

    free(msg);

  }

  if (fsm_mode <= FSMONITOR_MODE_DISABLED ||

      istate->fsmonitor_has_run_once)

    return;

  istate->fsmonitor_has_run_once = 1;

  trace_printf_key(&trace_fsmonitor, "refresh fsmonitor");

  if (fsm_mode == FSMONITOR_MODE_IPC) {

    query_success = !fsmonitor_ipc__send_query(

      istate->fsmonitor_last_update ?

      istate->fsmonitor_last_update : "builtin:fake",

      &query_result);

    if (query_success) {

      /*

       * The response contains a series of nul terminated

       * strings.  The first is the new token.

       *

       * Use `char *buf` as an interlude to trick the CI

       * static analysis to let us use `strbuf_addstr()`

       * here (and only copy the token) rather than

       * `strbuf_addbuf()`.

       */

      buf = query_result.buf;

      strbuf_addstr(&last_update_token, buf);

      bol = last_update_token.len + 1;

      is_trivial = query_result.buf[bol] == '/';

      if (is_trivial)

        trace2_data_intmax("fsm_client", NULL,

               "query/trivial-response", 1);

    } else {

      /*

       * The builtin daemon is not available on this

       * platform -OR- we failed to get a response.

       *

       * Generate a fake token (rather than a V1

       * timestamp) for the index extension.  (If

       * they switch back to the hook API, we don't

       * want ambiguous state.)

       */

      strbuf_addstr(&last_update_token, "builtin:fake");

    }

    goto apply_results;

  }

  assert(fsm_mode == FSMONITOR_MODE_HOOK);

  hook_version = fsmonitor_hook_version();

  /*

   * This could be racy so save the date/time now and query_fsmonitor_hook

   * should be inclusive to ensure we don't miss potential changes.

   */

  last_update = getnanotime();

  if (hook_version == HOOK_INTERFACE_VERSION1)

    strbuf_addf(&last_update_token, "%"PRIu64"", last_update);

  /*

   * If we have a last update token, call query_fsmonitor_hook for the set of

   * changes since that token, else assume everything is possibly dirty

   * and check it all.

   */

  if (istate->fsmonitor_last_update) {

    if (hook_version == -1 || hook_version == HOOK_INTERFACE_VERSION2) {

      query_success = !query_fsmonitor_hook(

        r, HOOK_INTERFACE_VERSION2,

        istate->fsmonitor_last_update, &query_result);

      if (query_success) {

        if (hook_version < 0)

          hook_version = HOOK_INTERFACE_VERSION2;

        /*

         * First entry will be the last update token

         * Need to use a char * variable because static

         * analysis was suggesting to use strbuf_addbuf

         * but we don't want to copy the entire strbuf

         * only the chars up to the first NUL

         */

        buf = query_result.buf;

        strbuf_addstr(&last_update_token, buf);

        if (!last_update_token.len) {

          warning("Empty last update token.");

          query_success = 0;

        } else {

          bol = last_update_token.len + 1;

          is_trivial = query_result.buf[bol] == '/';

        }

      } else if (hook_version < 0) {

        hook_version = HOOK_INTERFACE_VERSION1;

        if (!last_update_token.len)

          strbuf_addf(&last_update_token, "%"PRIu64"", last_update);

      }

    }

    if (hook_version == HOOK_INTERFACE_VERSION1) {

      query_success = !query_fsmonitor_hook(

        r, HOOK_INTERFACE_VERSION1,

        istate->fsmonitor_last_update, &query_result);

      if (query_success)

        is_trivial = query_result.buf[0] == '/';

    }

    if (is_trivial)

      trace2_data_intmax("fsm_hook", NULL,

             "query/trivial-response", 1);

    trace_performance_since(last_update, "fsmonitor process '%s'",

          fsm_settings__get_hook_path(r));

    trace_printf_key(&trace_fsmonitor,

         "fsmonitor process '%s' returned %s",

         fsm_settings__get_hook_path(r),

         query_success ? "success" : "failure");

  }

apply_results:

  /*

   * The response from FSMonitor (excluding the header token) is

   * either:

   *

   * [a] a (possibly empty) list of NUL delimited relative

   *     pathnames of changed paths.  This list can contain

   *     files and directories.  Directories have a trailing

   *     slash.

   *

   * [b] a single '/' to indicate the provider had no

   *     information and that we should consider everything

   *     invalid.  We call this a trivial response.

   */

  trace2_region_enter("fsmonitor", "apply_results", istate->repo);

  if (query_success && !is_trivial) {

    /*

     * Mark all pathnames returned by the monitor as dirty.

     *

     * This updates both the cache-entries and the untracked-cache.

     */

    int count = 0;

    buf = query_result.buf;

    for (i = bol; i < query_result.len; i++) {

      if (buf[i] != '\0')

        continue;

      fsmonitor_refresh_callback(istate, buf + bol);

      bol = i + 1;

      count++;

    }

    if (bol < query_result.len) {

      fsmonitor_refresh_callback(istate, buf + bol);

      count++;

    }

    /* Now mark the untracked cache for fsmonitor usage */

    if (istate->untracked)

      istate->untracked->use_fsmonitor = 1;

    if (count > fsmonitor_force_update_threshold)

      istate->cache_changed |= FSMONITOR_CHANGED;

    trace2_data_intmax("fsmonitor", istate->repo, "apply_count",

           count);

  } else {

    /*

     * We failed to get a response or received a trivial response,

     * so invalidate everything.

     *

     * We only want to run the post index changed hook if

     * we've actually changed entries, so keep track if we

     * actually changed entries or not.

     */

    int is_cache_changed = 0;

    for (i = 0; i < istate->cache_nr; i++) {

      if (istate->cache[i]->ce_flags & CE_FSMONITOR_VALID) {

        is_cache_changed = 1;

        istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;

      }

    }

    /*

     * If we're going to check every file, ensure we save

     * the results.

     */

    if (is_cache_changed)

      istate->cache_changed |= FSMONITOR_CHANGED;

    if (istate->untracked)

      istate->untracked->use_fsmonitor = 0;

  }

  trace2_region_leave("fsmonitor", "apply_results", istate->repo);

  strbuf_release(&query_result);

  /* Now that we've updated istate, save the last_update_token */

  FREE_AND_NULL(istate->fsmonitor_last_update);

  istate->fsmonitor_last_update = strbuf_detach(&last_update_token, NULL);

}

/*

 * The caller wants to turn on FSMonitor.  And when the caller writes

 * the index to disk, a FSMonitor extension should be included.  This

 * requires that `istate->fsmonitor_last_update` not be NULL.  But we

 * have not actually talked to a FSMonitor process yet, so we don't

 * have an initial value for this field.

 *

 * For a protocol V1 FSMonitor process, this field is a formatted

 * "nanoseconds since epoch" field.  However, for a protocol V2

 * FSMonitor process, this field is an opaque token.

 *

 * Historically, `add_fsmonitor()` has initialized this field to the

 * current time for protocol V1 processes.  There are lots of race

 * conditions here, but that code has shipped...

 *

 * The only true solution is to use a V2 FSMonitor and get a current

 * or default token value (that it understands), but we cannot do that

 * until we have actually talked to an instance of the FSMonitor process

 * (but the protocol requires that we send a token first...).

 *

 * For simplicity, just initialize like we have a V1 process and require

 * that V2 processes adapt.

 */

static void initialize_fsmonitor_last_update(struct index_state *istate)

{

  struct strbuf last_update = STRBUF_INIT;

  strbuf_addf(&last_update, "%"PRIu64"", getnanotime());

  istate->fsmonitor_last_update = strbuf_detach(&last_update, NULL);

}

void add_fsmonitor(struct index_state *istate)

{

  unsigned int i;

  if (!istate->fsmonitor_last_update) {

    trace_printf_key(&trace_fsmonitor, "add fsmonitor");

    istate->cache_changed |= FSMONITOR_CHANGED;

    initialize_fsmonitor_last_update(istate);

    /* reset the fsmonitor state */

    for (i = 0; i < istate->cache_nr; i++)

      istate->cache[i]->ce_flags &= ~CE_FSMONITOR_VALID;

    /* reset the untracked cache */

    if (istate->untracked) {

      add_untracked_cache(istate);

      istate->untracked->use_fsmonitor = 1;

    }

    /* Update the fsmonitor state */

    refresh_fsmonitor(istate);

  }

}

void remove_fsmonitor(struct index_state *istate)

{

  if (istate->fsmonitor_last_update) {

    trace_printf_key(&trace_fsmonitor, "remove fsmonitor");

    istate->cache_changed |= FSMONITOR_CHANGED;

    FREE_AND_NULL(istate->fsmonitor_last_update);

  }

}

void tweak_fsmonitor(struct index_state *istate)

{

  unsigned int i;

  int fsmonitor_enabled = (fsm_settings__get_mode(istate->repo)

         > FSMONITOR_MODE_DISABLED);

  if (istate->fsmonitor_dirty) {

    if (fsmonitor_enabled) {

      /* Mark all entries valid */

      for (i = 0; i < istate->cache_nr; i++) {

        if (S_ISGITLINK(istate->cache[i]->ce_mode))

          continue;

        istate->cache[i]->ce_flags |= CE_FSMONITOR_VALID;

      }

      /* Mark all previously saved entries as dirty */

      assert_index_minimum(istate, istate->fsmonitor_dirty->bit_size);

      ewah_each_bit(istate->fsmonitor_dirty, fsmonitor_ewah_callback, istate);

      refresh_fsmonitor(istate);

    }

    ewah_free(istate->fsmonitor_dirty);

    istate->fsmonitor_dirty = NULL;

  }

  if (fsmonitor_enabled)

    add_fsmonitor(istate);

  else

    remove_fsmonitor(istate);

}