From bc41f93e90f6edcc9067f3bc1085bb6c85082c00 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Zbigniew=20J=C4=99drzejewski-Szmek?= Date: Sun, 3 Mar 2013 01:32:34 -0500 Subject: [PATCH] core/path: install inotify watches top-down instead of bottom-up When watches are installed from the bottom, it is always possible to race, and miss a file creation event. The race can be avoided if a watch is first established for a parent directory, and then for the file in the directory. If the file is created in the time between, the watch on the parent directory will fire. Some messages (mostly at debug level) are added to help diagnose pidfile issues. Should fix https://bugzilla.redhat.com/show_bug.cgi?id=917075. --- src/core/path.c | 78 ++++++++++++++++++++++++++++------------------ src/core/service.c | 16 ++++++++-- 2 files changed, 62 insertions(+), 32 deletions(-) diff --git a/src/core/path.c b/src/core/path.c index fc101280a..01a2b0810 100644 --- a/src/core/path.c +++ b/src/core/path.c @@ -53,8 +53,8 @@ int path_spec_watch(PathSpec *s, Unit *u) { }; bool exists = false; - char _cleanup_free_ *k = NULL; - char *slash; + char _cleanup_free_ *path = NULL; + char *slash, *oldslash = NULL; int r; assert(u); @@ -62,8 +62,8 @@ int path_spec_watch(PathSpec *s, Unit *u) { path_spec_unwatch(s, u); - k = strdup(s->path); - if (!k) + path = strdup(s->path); + if (!path) return -ENOMEM; s->inotify_fd = inotify_init1(IN_NONBLOCK|IN_CLOEXEC); @@ -76,43 +76,61 @@ int path_spec_watch(PathSpec *s, Unit *u) { if (r < 0) goto fail; - s->primary_wd = inotify_add_watch(s->inotify_fd, k, flags_table[s->type]); - if (s->primary_wd >= 0) - exists = true; - else if (errno != EACCES && errno != ENOENT) { - log_error("Failed to add watch on %s: %m", k); - r = -errno; - goto fail; - } + /* This assumes the path was passed through path_kill_slashes()! */ - do { + for(slash = strchr(path, '/'); ; slash = strchr(slash+1, '/')) { int flags; + char tmp; + + if (slash) { + tmp = slash[slash == path]; + slash[slash == path] = '\0'; + flags = IN_MOVE_SELF | IN_DELETE_SELF | IN_ATTRIB | IN_CREATE | IN_MOVED_TO; + } else { + flags = flags_table[s->type]; + } - /* This assumes the path was passed through path_kill_slashes()! */ - slash = strrchr(k, '/'); - if (!slash) - break; - - /* Trim the path at the last slash. Keep the slash if it's the root dir. */ - slash[slash == k] = 0; - - flags = IN_MOVE_SELF; - if (!exists) - flags |= IN_DELETE_SELF | IN_ATTRIB | IN_CREATE | IN_MOVED_TO; + r = inotify_add_watch(s->inotify_fd, path, flags); + if (r < 0) { + if (errno == EACCES || errno == ENOENT) + break; - if (inotify_add_watch(s->inotify_fd, k, flags) >= 0) - exists = true; - else if (errno != EACCES && errno != ENOENT) { - log_error("Failed to add watch on %s: %m", k); + log_warning("Failed to add watch on %s: %m", path); r = -errno; goto fail; + } else { + exists = true; + + /* Path exists, we don't need to watch parent + too closely. */ + if (oldslash) { + char tmp2 = oldslash[oldslash == path]; + oldslash[oldslash == path] = '\0'; + + inotify_add_watch(s->inotify_fd, path, IN_MOVE_SELF); + /* Error is ignored, the worst can happen is + we get spurious events. */ + + oldslash[oldslash == path] = tmp2; + } } - } while (slash != k); + + if (slash) { + slash[slash == path] = tmp; + oldslash = slash; + } else { + /* whole path has been iterated over */ + s->primary_wd = r; + break; + } + } + + assert(errno == EACCES || errno == ENOENT || streq(path, s->path)); if (!exists) { log_error("Failed to add watch on any of the components of %s: %m", s->path); - r = -errno; + r = -errno; /* either EACCESS or ENOENT */ goto fail; } diff --git a/src/core/service.c b/src/core/service.c index 3f8aabcf4..61b150cba 100644 --- a/src/core/service.c +++ b/src/core/service.c @@ -1400,8 +1400,13 @@ static int service_load_pid_file(Service *s, bool may_warn) { } r = parse_pid(k, &pid); - if (r < 0) + if (r < 0) { + if (may_warn) + log_info_unit(UNIT(s)->id, + "Failed to read PID from file %s: %s", + s->pid_file, strerror(-r)); return r; + } if (kill(pid, 0) < 0 && errno != EPERM) { if (may_warn) @@ -1429,9 +1434,13 @@ static int service_load_pid_file(Service *s, bool may_warn) { return r; r = unit_watch_pid(UNIT(s), pid); - if (r < 0) + if (r < 0) { /* FIXME: we need to do something here */ + log_warning_unit(UNIT(s)->id, + "Failed to watch PID %lu from service %s", + (unsigned long) pid, UNIT(s)->id); return r; + } return 0; } @@ -2824,6 +2833,9 @@ static int service_watch_pid_file(Service *s) { goto fail; /* the pidfile might have appeared just before we set the watch */ + log_debug_unit(UNIT(s)->id, + "Trying to read %s's PID file %s in case it changed", + UNIT(s)->id, s->pid_file_pathspec->path); service_retry_pid_file(s); return 0; -- 2.30.2