From patchwork Thu Oct 21 14:25:07 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Hostetler X-Patchwork-Id: 12575243 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 402FFC433EF for ; Thu, 21 Oct 2021 14:26:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 262D06120F for ; Thu, 21 Oct 2021 14:26:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231667AbhJUO2Z (ORCPT ); Thu, 21 Oct 2021 10:28:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38420 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231474AbhJUO1o (ORCPT ); Thu, 21 Oct 2021 10:27:44 -0400 Received: from mail-wr1-x42e.google.com (mail-wr1-x42e.google.com [IPv6:2a00:1450:4864:20::42e]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 8E498C061228 for ; Thu, 21 Oct 2021 07:25:28 -0700 (PDT) Received: by mail-wr1-x42e.google.com with SMTP id y3so1463281wrl.1 for ; Thu, 21 Oct 2021 07:25:28 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20210112; h=message-id:in-reply-to:references:from:date:subject:fcc :content-transfer-encoding:mime-version:to:cc; bh=5yNSyAaB0Fw1qxk/ETTZ28zRlk4xlGsS1KF+lI4My2k=; b=orE2FDcAb8dhRML0TAVJwrSYEgqsi+lknOS9vs/VEWZArNmq230fG3rOaJR0kIxlI+ yyIOeNpwQOR6w4zq4BEVYl6EOVsGkgm9ut9ARa4yKyDw8i84Cr+5S0sGodjF7SuFaxp1 SVrR1ievUrxCQFA8XnjU5HEcAkK/UC1cq5Nb5re5fbnDq4wG8iOYSsSFvNgK0fHmLEFL TrhGjFKzrpkkatUP71jy0CoARP932EOzFPJXoxOKTviL8dk+OYAAq9erC7mtm0lRnwRl CxFSKVisbRF4JyTVNObcy0tP2eX0cVUPt9gGp5CL7RNp4AwCpUIZr2M4wGYx2Z+6+CJt 86Ww== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=x-gm-message-state:message-id:in-reply-to:references:from:date :subject:fcc:content-transfer-encoding:mime-version:to:cc; bh=5yNSyAaB0Fw1qxk/ETTZ28zRlk4xlGsS1KF+lI4My2k=; b=yTPsJL8fi684xPGqwYpwGhYuB2/0kT60JBr8x6/7UIwsYKIxTDwmPb8WKBK/0wH8gk 74Fy0lC49TqRJHJOKudjD6gJBRYDswkg9tPTha41IW1urD3QS21XVdkffwvzp1QqwEgs bPRVrtNJWb2qrF1xHABY6EjYszkj1+CrnLuCikLUGClgzpeP5N6fqHgxt3Nydg1Dir5P JU7YI5pfeHrkOVb/7tvj4l3NnmuoMZrZVZXAonYfz3q+0VeoHHSVkMahZK9RVsy94UJQ pHAkJ+VJ/PC8HI2XZsT/vQ475/iQiJCsiFvSOVkbWFBKku+7W3/4fgwrSA9GSXjmgNrM XJUQ== X-Gm-Message-State: AOAM5326WpiUzZ3cCE+BsSCASfnnqWaDRzWt4K8BwejUYm+HnbM3sqjA MFVjQiYmwdmgo865G7MrGyaDo0B/Ojk= X-Google-Smtp-Source: ABdhPJyjpyXC63q7kATr6HDCWoeCueiZS19Jt8Mx7CSpar0POqRHIbQbdjkOSqhcTWAh+b0zxabwWg== X-Received: by 2002:adf:bc4a:: with SMTP id a10mr7932459wrh.131.1634826327144; Thu, 21 Oct 2021 07:25:27 -0700 (PDT) Received: from [127.0.0.1] ([13.74.141.28]) by smtp.gmail.com with ESMTPSA id u5sm5258923wrg.57.2021.10.21.07.25.26 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 21 Oct 2021 07:25:26 -0700 (PDT) Message-Id: <1e2bd77fcea7beab17eeec8ea68c4ffbc4541655.1634826309.git.gitgitgadget@gmail.com> In-Reply-To: References: Date: Thu, 21 Oct 2021 14:25:07 +0000 Subject: [PATCH v4 27/29] fsmonitor--daemon: use a cookie file to sync with file system Fcc: Sent MIME-Version: 1.0 To: git@vger.kernel.org Cc: Jeff Hostetler , Jeff Hostetler , Jeff Hostetler Precedence: bulk List-ID: X-Mailing-List: git@vger.kernel.org From: Jeff Hostetler From: Jeff Hostetler Teach fsmonitor--daemon client threads to create a cookie file inside the .git directory and then wait until FS events for the cookie are observed by the FS listener thread. This helps address the racy nature of file system events by blocking the client response until the kernel has drained any event backlog. This is especially important on MacOS where kernel events are only issued with a limited frequency. See the `latency` argument of `FSeventStreamCreate()`. The kernel only signals every `latency` seconds, but does not guarantee that the kernel queue is completely drained, so we may have to wait more than one interval. If we increase the frequency, the system is more likely to drop events. We avoid these issues by having each client thread create a unique cookie file and then wait until it is seen in the event stream. Co-authored-by: Kevin Willford Co-authored-by: Johannes Schindelin Signed-off-by: Jeff Hostetler --- builtin/fsmonitor--daemon.c | 228 +++++++++++++++++++++++++++++++++++- fsmonitor--daemon.h | 5 + 2 files changed, 232 insertions(+), 1 deletion(-) diff --git a/builtin/fsmonitor--daemon.c b/builtin/fsmonitor--daemon.c index 962b24569e1..6011fe42ee0 100644 --- a/builtin/fsmonitor--daemon.c +++ b/builtin/fsmonitor--daemon.c @@ -94,6 +94,149 @@ static int do_as_client__status(void) } } +enum fsmonitor_cookie_item_result { + FCIR_ERROR = -1, /* could not create cookie file ? */ + FCIR_INIT = 0, + FCIR_SEEN, + FCIR_ABORT, +}; + +struct fsmonitor_cookie_item { + struct hashmap_entry entry; + const char *name; + enum fsmonitor_cookie_item_result result; +}; + +static int cookies_cmp(const void *data, const struct hashmap_entry *he1, + const struct hashmap_entry *he2, const void *keydata) +{ + const struct fsmonitor_cookie_item *a = + container_of(he1, const struct fsmonitor_cookie_item, entry); + const struct fsmonitor_cookie_item *b = + container_of(he2, const struct fsmonitor_cookie_item, entry); + + return strcmp(a->name, keydata ? keydata : b->name); +} + +static enum fsmonitor_cookie_item_result with_lock__wait_for_cookie( + struct fsmonitor_daemon_state *state) +{ + /* assert current thread holding state->main_lock */ + + int fd; + struct fsmonitor_cookie_item *cookie; + struct strbuf cookie_pathname = STRBUF_INIT; + struct strbuf cookie_filename = STRBUF_INIT; + enum fsmonitor_cookie_item_result result; + int my_cookie_seq; + + CALLOC_ARRAY(cookie, 1); + + my_cookie_seq = state->cookie_seq++; + + strbuf_addf(&cookie_filename, "%i-%i", getpid(), my_cookie_seq); + + strbuf_addbuf(&cookie_pathname, &state->path_cookie_prefix); + strbuf_addbuf(&cookie_pathname, &cookie_filename); + + cookie->name = strbuf_detach(&cookie_filename, NULL); + cookie->result = FCIR_INIT; + hashmap_entry_init(&cookie->entry, strhash(cookie->name)); + + hashmap_add(&state->cookies, &cookie->entry); + + trace_printf_key(&trace_fsmonitor, "cookie-wait: '%s' '%s'", + cookie->name, cookie_pathname.buf); + + /* + * Create the cookie file on disk and then wait for a notification + * that the listener thread has seen it. + */ + fd = open(cookie_pathname.buf, O_WRONLY | O_CREAT | O_EXCL, 0600); + if (fd >= 0) { + close(fd); + unlink(cookie_pathname.buf); + + /* + * NEEDSWORK: This is an infinite wait (well, unless another + * thread sends us an abort). I'd like to change this to + * use `pthread_cond_timedwait()` and return an error/timeout + * and let the caller do the trivial response thing. + */ + while (cookie->result == FCIR_INIT) + pthread_cond_wait(&state->cookies_cond, + &state->main_lock); + } else { + error_errno(_("could not create fsmonitor cookie '%s'"), + cookie->name); + + cookie->result = FCIR_ERROR; + } + + hashmap_remove(&state->cookies, &cookie->entry, NULL); + + result = cookie->result; + + free((char*)cookie->name); + free(cookie); + strbuf_release(&cookie_pathname); + + return result; +} + +/* + * Mark these cookies as _SEEN and wake up the corresponding client threads. + */ +static void with_lock__mark_cookies_seen(struct fsmonitor_daemon_state *state, + const struct string_list *cookie_names) +{ + /* assert current thread holding state->main_lock */ + + int k; + int nr_seen = 0; + + for (k = 0; k < cookie_names->nr; k++) { + struct fsmonitor_cookie_item key; + struct fsmonitor_cookie_item *cookie; + + key.name = cookie_names->items[k].string; + hashmap_entry_init(&key.entry, strhash(key.name)); + + cookie = hashmap_get_entry(&state->cookies, &key, entry, NULL); + if (cookie) { + trace_printf_key(&trace_fsmonitor, "cookie-seen: '%s'", + cookie->name); + cookie->result = FCIR_SEEN; + nr_seen++; + } + } + + if (nr_seen) + pthread_cond_broadcast(&state->cookies_cond); +} + +/* + * Set _ABORT on all pending cookies and wake up all client threads. + */ +static void with_lock__abort_all_cookies(struct fsmonitor_daemon_state *state) +{ + /* assert current thread holding state->main_lock */ + + struct hashmap_iter iter; + struct fsmonitor_cookie_item *cookie; + int nr_aborted = 0; + + hashmap_for_each_entry(&state->cookies, &iter, cookie, entry) { + trace_printf_key(&trace_fsmonitor, "cookie-abort: '%s'", + cookie->name); + cookie->result = FCIR_ABORT; + nr_aborted++; + } + + if (nr_aborted) + pthread_cond_broadcast(&state->cookies_cond); +} + /* * Requests to and from a FSMonitor Protocol V2 provider use an opaque * "token" as a virtual timestamp. Clients can request a summary of all @@ -391,6 +534,9 @@ static void fsmonitor_free_token_data(struct fsmonitor_token_data *token) * We should create a new token and start fresh (as if we just * booted up). * + * [2] Some of those lost events may have been for cookie files. We + * should assume the worst and abort them rather letting them starve. + * * If there are no concurrent threads readering the current token data * series, we can free it now. Otherwise, let the last reader free * it. @@ -412,6 +558,8 @@ static void with_lock__do_force_resync(struct fsmonitor_daemon_state *state) state->current_token_data = new_one; fsmonitor_free_token_data(free_me); + + with_lock__abort_all_cookies(state); } void fsmonitor_force_resync(struct fsmonitor_daemon_state *state) @@ -487,6 +635,8 @@ static int do_handle_client(struct fsmonitor_daemon_state *state, int hash_ret; int do_trivial = 0; int do_flush = 0; + int do_cookie = 0; + enum fsmonitor_cookie_item_result cookie_result; /* * We expect `command` to be of the form: @@ -547,6 +697,7 @@ static int do_handle_client(struct fsmonitor_daemon_state *state, * We have a V2 valid token: * "builtin::" */ + do_cookie = 1; } } @@ -555,6 +706,30 @@ static int do_handle_client(struct fsmonitor_daemon_state *state, if (!state->current_token_data) BUG("fsmonitor state does not have a current token"); + /* + * Write a cookie file inside the directory being watched in + * an effort to flush out existing filesystem events that we + * actually care about. Suspend this client thread until we + * see the filesystem events for this cookie file. + * + * Creating the cookie lets us guarantee that our FS listener + * thread has drained the kernel queue and we are caught up + * with the kernel. + * + * If we cannot create the cookie (or otherwise guarantee that + * we are caught up), we send a trivial response. We have to + * assume that there might be some very, very recent activity + * on the FS still in flight. + */ + if (do_cookie) { + cookie_result = with_lock__wait_for_cookie(state); + if (cookie_result != FCIR_SEEN) { + error(_("fsmonitor: cookie_result '%d' != SEEN"), + cookie_result); + do_trivial = 1; + } + } + if (do_flush) with_lock__do_force_resync(state); @@ -775,7 +950,9 @@ static int handle_client(void *data, return result; } -#define FSMONITOR_COOKIE_PREFIX ".fsmonitor-daemon-" +#define FSMONITOR_DIR "fsmonitor--daemon" +#define FSMONITOR_COOKIE_DIR "cookies" +#define FSMONITOR_COOKIE_PREFIX (FSMONITOR_DIR "/" FSMONITOR_COOKIE_DIR "/") enum fsmonitor_path_type fsmonitor_classify_path_workdir_relative( const char *rel) @@ -928,6 +1105,9 @@ void fsmonitor_publish(struct fsmonitor_daemon_state *state, } } + if (cookie_names->nr) + with_lock__mark_cookies_seen(state, cookie_names); + pthread_mutex_unlock(&state->main_lock); } @@ -1019,7 +1199,9 @@ static int fsmonitor_run_daemon(void) memset(&state, 0, sizeof(state)); + hashmap_init(&state.cookies, cookies_cmp, NULL, 0); pthread_mutex_init(&state.main_lock, NULL); + pthread_cond_init(&state.cookies_cond, NULL); state.error_code = 0; state.current_token_data = fsmonitor_new_token_data(); @@ -1044,6 +1226,44 @@ static int fsmonitor_run_daemon(void) state.nr_paths_watching = 2; } + /* + * We will write filesystem syncing cookie files into + * ///-. + * + * The extra layers of subdirectories here keep us from + * changing the mtime on ".git/" or ".git/foo/" when we create + * or delete cookie files. + * + * There have been problems with some IDEs that do a + * non-recursive watch of the ".git/" directory and run a + * series of commands any time something happens. + * + * For example, if we place our cookie files directly in + * ".git/" or ".git/foo/" then a `git status` (or similar + * command) from the IDE will cause a cookie file to be + * created in one of those dirs. This causes the mtime of + * those dirs to change. This triggers the IDE's watch + * notification. This triggers the IDE to run those commands + * again. And the process repeats and the machine never goes + * idle. + * + * Adding the extra layers of subdirectories prevents the + * mtime of ".git/" and ".git/foo" from changing when a + * cookie file is created. + */ + strbuf_init(&state.path_cookie_prefix, 0); + strbuf_addbuf(&state.path_cookie_prefix, &state.path_gitdir_watch); + + strbuf_addch(&state.path_cookie_prefix, '/'); + strbuf_addstr(&state.path_cookie_prefix, FSMONITOR_DIR); + mkdir(state.path_cookie_prefix.buf, 0777); + + strbuf_addch(&state.path_cookie_prefix, '/'); + strbuf_addstr(&state.path_cookie_prefix, FSMONITOR_COOKIE_DIR); + mkdir(state.path_cookie_prefix.buf, 0777); + + strbuf_addch(&state.path_cookie_prefix, '/'); + /* * Confirm that we can create platform-specific resources for the * filesystem listener before we bother starting all the threads. @@ -1056,6 +1276,7 @@ static int fsmonitor_run_daemon(void) err = fsmonitor_run_daemon_1(&state); done: + pthread_cond_destroy(&state.cookies_cond); pthread_mutex_destroy(&state.main_lock); fsm_listen__dtor(&state); @@ -1063,6 +1284,11 @@ done: strbuf_release(&state.path_worktree_watch); strbuf_release(&state.path_gitdir_watch); + strbuf_release(&state.path_cookie_prefix); + + /* + * NEEDSWORK: Consider "rm -rf /" + */ return err; } diff --git a/fsmonitor--daemon.h b/fsmonitor--daemon.h index 20a815d80f8..c16ef095688 100644 --- a/fsmonitor--daemon.h +++ b/fsmonitor--daemon.h @@ -45,6 +45,11 @@ struct fsmonitor_daemon_state { struct fsmonitor_token_data *current_token_data; + struct strbuf path_cookie_prefix; + pthread_cond_t cookies_cond; + int cookie_seq; + struct hashmap cookies; + int error_code; struct fsmonitor_daemon_backend_data *backend_data;