On Thu, Sep 14, 2023 at 04:51:30PM +0200, mwilck@xxxxxxxx wrote:
> From: Martin Wilck <mwilck@xxxxxxxx>
>
> Since "libmultipath: keep bindings in memory", we don't re-read the
> bindings file after every modification. Add a notification mechanism
> that makes multipathd aware of changes to the bindings file. Because
> multipathd itself will change the bindings file, it must compare
> timestamps in order to avoid reading the file repeatedly.
>
> Because select_alias() can be called from multiple thread contexts (uxlsnr,
> uevent handler), we need to add locking for the bindings file. The
> timestamp must also be protected by a lock, because it can't be read
> or written atomically.
>
> Note: The notification mechanism expects the bindings file to be
> atomically replaced by rename(2). Changes must be made in a temporary file and
> applied using rename(2), as in update_bindings_file(). The inotify
> mechanism deliberately does not listen to close-after-write events
> that would be generated by editing the bindings file directly. This
>
> Note also: new bindings will only be read from add_map_with_path(),
> i.e. either during reconfigure(), or when a new map is created during
> runtime. Existing maps will not be renamed if the binding file changes,
> unless the user runs "multipathd reconfigure". This is not a change
> wrt the previous code, but it should be mentioned anyway.
>
Reviewed-by: Benjamin Marzinski <bmarzins@xxxxxxxxxx>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
>
> libmultipath: protect global_bindings with a mutex
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
>
> libmultipath: check timestamp of bindings file before reading it
>
> Signed-off-by: Martin Wilck <mwilck@xxxxxxxx>
> ---
> libmultipath/alias.c | 252 +++++++++++++++++++++++++-----
> libmultipath/alias.h | 3 +-
> libmultipath/libmultipath.version | 5 +
> multipathd/uxlsnr.c | 36 ++++-
> tests/alias.c | 3 +
> 5 files changed, 254 insertions(+), 45 deletions(-)
>
> diff --git a/libmultipath/alias.c b/libmultipath/alias.c
> index 66e34e3..964b8a7 100644
> --- a/libmultipath/alias.c
> +++ b/libmultipath/alias.c
> @@ -10,6 +10,7 @@
> #include <stdio.h>
> #include <stdbool.h>
> #include <assert.h>
> +#include <sys/inotify.h>
>
> #include "debug.h"
> #include "util.h"
> @@ -22,6 +23,7 @@
> #include "config.h"
> #include "devmapper.h"
> #include "strbuf.h"
> +#include "time-util.h"
>
> /*
> * significant parts of this file were taken from iscsi-bindings.c of the
> @@ -50,6 +52,12 @@
> "# alias wwid\n" \
> "#\n"
>
> +/* uatomic access only */
> +static int bindings_file_changed = 1;
> +
> +static pthread_mutex_t timestamp_mutex = PTHREAD_MUTEX_INITIALIZER;
> +static struct timespec bindings_last_updated;
> +
> struct binding {
> char *alias;
> char *wwid;
> @@ -60,6 +68,9 @@ struct binding {
> * an abstract type.
> */
> typedef struct _vector Bindings;
> +
> +/* Protect global_bindings */
> +static pthread_mutex_t bindings_mutex = PTHREAD_MUTEX_INITIALIZER;
> static Bindings global_bindings = { .allocated = 0 };
>
> enum {
> @@ -78,6 +89,27 @@ static void _free_binding(struct binding *bdg)
> free(bdg);
> }
>
> +static void free_bindings(Bindings *bindings)
> +{
> + struct binding *bdg;
> + int i;
> +
> + vector_foreach_slot(bindings, bdg, i)
> + _free_binding(bdg);
> + vector_reset(bindings);
> +}
> +
> +static void set_global_bindings(Bindings *bindings)
> +{
> + Bindings old_bindings;
> +
> + pthread_mutex_lock(&bindings_mutex);
> + old_bindings = global_bindings;
> + global_bindings = *bindings;
> + pthread_mutex_unlock(&bindings_mutex);
> + free_bindings(&old_bindings);
> +}
> +
> static const struct binding *get_binding_for_alias(const Bindings *bindings,
> const char *alias)
> {
> @@ -199,7 +231,8 @@ static int delete_binding(Bindings *bindings, const char *wwid)
> return BINDING_DELETED;
> }
>
> -static int write_bindings_file(const Bindings *bindings, int fd)
> +static int write_bindings_file(const Bindings *bindings, int fd,
> + struct timespec *ts)
> {
> struct binding *bnd;
> STRBUF_ON_STACK(content);
> @@ -227,9 +260,56 @@ static int write_bindings_file(const Bindings *bindings, int fd)
> }
> len -= n;
> }
> + fsync(fd);
> + if (ts) {
> + struct stat st;
> +
> + if (fstat(fd, &st) == 0)
> + *ts = st.st_mtim;
> + else
> + clock_gettime(CLOCK_REALTIME_COARSE, ts);
> + }
> return 0;
> }
>
> +void handle_bindings_file_inotify(const struct inotify_event *event)
> +{
> + struct config *conf;
> + const char *base;
> + bool changed = false;
> + struct stat st;
> + struct timespec ts = { 0, 0 };
> + int ret;
> +
> + if (!(event->mask & IN_MOVED_TO))
> + return;
> +
> + conf = get_multipath_config();
> + base = strrchr(conf->bindings_file, '/');
> + changed = base && base > conf->bindings_file &&
> + !strcmp(base + 1, event->name);
> + ret = stat(conf->bindings_file, &st);
> + put_multipath_config(conf);
> +
> + if (!changed)
> + return;
> +
> + pthread_mutex_lock(×tamp_mutex);
> + if (ret == 0) {
> + ts = st.st_mtim;
> + changed = timespeccmp(&ts, &bindings_last_updated) > 0;
> + }
> + pthread_mutex_unlock(×tamp_mutex);
> +
> + if (changed) {
> + uatomic_xchg(&bindings_file_changed, 1);
> + condlog(3, "%s: bindings file must be re-read, new timestamp: %ld.%06ld",
> + __func__, (long)ts.tv_sec, (long)ts.tv_nsec / 1000);
> + } else
> + condlog(3, "%s: bindings file is up-to-date, timestamp: %ld.%06ld",
> + __func__, (long)ts.tv_sec, (long)ts.tv_nsec / 1000);
> +}
> +
> static int update_bindings_file(const Bindings *bindings,
> const char *bindings_file)
> {
> @@ -237,6 +317,7 @@ static int update_bindings_file(const Bindings *bindings,
> int fd = -1;
> char tempname[PATH_MAX];
> mode_t old_umask;
> + struct timespec ts;
>
> if (safe_sprintf(tempname, "%s.XXXXXX", bindings_file))
> return -1;
> @@ -248,7 +329,7 @@ static int update_bindings_file(const Bindings *bindings,
> }
> umask(old_umask);
> pthread_cleanup_push(cleanup_fd_ptr, &fd);
> - rc = write_bindings_file(bindings, fd);
> + rc = write_bindings_file(bindings, fd, &ts);
> pthread_cleanup_pop(1);
> if (rc == -1) {
> condlog(1, "failed to write new bindings file");
> @@ -257,8 +338,12 @@ static int update_bindings_file(const Bindings *bindings,
> }
> if ((rc = rename(tempname, bindings_file)) == -1)
> condlog(0, "%s: rename: %m", __func__);
> - else
> + else {
> + pthread_mutex_lock(×tamp_mutex);
> + bindings_last_updated = ts;
> + pthread_mutex_unlock(×tamp_mutex);
> condlog(1, "updated bindings file %s", bindings_file);
> + }
> return rc;
> }
>
> @@ -387,6 +472,7 @@ int get_free_id(const Bindings *bindings, const char *prefix, const char *map_ww
> return id;
> }
>
> +/* Called with binding_mutex held */
> static char *
> allocate_binding(const char *filename, const char *wwid, int id, const char *prefix)
> {
> @@ -423,6 +509,30 @@ allocate_binding(const char *filename, const char *wwid, int id, const char *pre
> return alias;
> }
>
> +enum {
> + BINDINGS_FILE_UP2DATE,
> + BINDINGS_FILE_READ,
> + BINDINGS_FILE_ERROR,
> + BINDINGS_FILE_BAD,
> +};
> +
> +static int _read_bindings_file(const struct config *conf, Bindings *bindings,
> + bool force);
> +
> +static void read_bindings_file(void)
> +{
> + struct config *conf;
> + Bindings bindings = {.allocated = 0, };
> + int rc;
> +
> + conf = get_multipath_config();
> + pthread_cleanup_push(put_multipath_config, conf);
> + rc = _read_bindings_file(conf, &bindings, false);
> + pthread_cleanup_pop(1);
> + if (rc == BINDINGS_FILE_READ)
> + set_global_bindings(&bindings);
> +}
> +
> /*
> * get_user_friendly_alias() action table
> *
> @@ -463,6 +573,11 @@ char *get_user_friendly_alias(const char *wwid, const char *file, const char *al
> bool new_binding = false;
> const struct binding *bdg;
>
> + read_bindings_file();
> +
> + pthread_mutex_lock(&bindings_mutex);
> + pthread_cleanup_push(cleanup_mutex, &bindings_mutex);
> +
> if (!*alias_old)
> goto new_alias;
>
> @@ -514,40 +629,40 @@ new_alias:
> alias, wwid);
>
> out:
> + /* unlock bindings_mutex */
> + pthread_cleanup_pop(1);
> return alias;
> }
>
> int get_user_friendly_wwid(const char *alias, char *buff)
> {
> const struct binding *bdg;
> + int rc = -1;
>
> if (!alias || *alias == '\0') {
> condlog(3, "Cannot find binding for empty alias");
> return -1;
> }
>
> + read_bindings_file();
> +
> + pthread_mutex_lock(&bindings_mutex);
> + pthread_cleanup_push(cleanup_mutex, &bindings_mutex);
> bdg = get_binding_for_alias(&global_bindings, alias);
> - if (!bdg) {
> + if (bdg) {
> + strlcpy(buff, bdg->wwid, WWID_SIZE);
> + rc = 0;
> + } else
> *buff = '\0';
> - return -1;
> - }
> - strlcpy(buff, bdg->wwid, WWID_SIZE);
> - return 0;
> -}
> -
> -static void free_bindings(Bindings *bindings)
> -{
> - struct binding *bdg;
> - int i;
> -
> - vector_foreach_slot(bindings, bdg, i)
> - _free_binding(bdg);
> - vector_reset(bindings);
> + pthread_cleanup_pop(1);
> + return rc;
> }
>
> void cleanup_bindings(void)
> {
> + pthread_mutex_lock(&bindings_mutex);
> free_bindings(&global_bindings);
> + pthread_mutex_unlock(&bindings_mutex);
> }
>
> enum {
> @@ -595,7 +710,20 @@ static int _check_bindings_file(const struct config *conf, FILE *file,
> char *line = NULL;
> size_t line_len = 0;
> ssize_t n;
> + char header[sizeof(BINDINGS_FILE_HEADER)];
>
> + header[sizeof(BINDINGS_FILE_HEADER) - 1] = '\0';
> + if (fread(header, sizeof(BINDINGS_FILE_HEADER) - 1, 1, file) < 1) {
> + condlog(2, "%s: failed to read header from %s", __func__,
> + conf->bindings_file);
> + fseek(file, 0, SEEK_SET);
> + rc = -1;
> + } else if (strcmp(header, BINDINGS_FILE_HEADER)) {
> + condlog(2, "%s: invalid header in %s", __func__,
> + conf->bindings_file);
> + fseek(file, 0, SEEK_SET);
> + rc = -1;
> + }
> pthread_cleanup_push(cleanup_free_ptr, &line);
> while ((n = getline(&line, &line_len, file)) >= 0) {
> char *alias, *wwid;
> @@ -643,6 +771,68 @@ static int mp_alias_compar(const void *p1, const void *p2)
> &((*(struct mpentry * const *)p2)->alias));
> }
>
> +static int _read_bindings_file(const struct config *conf, Bindings *bindings,
> + bool force)
> +{
> + int can_write;
> + int rc = 0, ret, fd;
> + FILE *file;
> + struct stat st;
> + int has_changed = uatomic_xchg(&bindings_file_changed, 0);
> +
> + if (!force) {
> + if (!has_changed) {
> + condlog(4, "%s: bindings are unchanged", __func__);
> + return BINDINGS_FILE_UP2DATE;
> + }
> + }
> +
> + fd = open_file(conf->bindings_file, &can_write, BINDINGS_FILE_HEADER);
> + if (fd == -1)
> + return BINDINGS_FILE_ERROR;
> +
> + file = fdopen(fd, "r");
> + if (file != NULL) {
> + condlog(3, "%s: reading %s", __func__, conf->bindings_file);
> +
> + pthread_cleanup_push(cleanup_fclose, file);
> + ret = _check_bindings_file(conf, file, bindings);
> + if (ret == 0) {
> + struct timespec ts;
> +
> + rc = BINDINGS_FILE_READ;
> + ret = fstat(fd, &st);
> + if (ret == 0)
> + ts = st.st_mtim;
> + else {
> + condlog(1, "%s: fstat failed (%m), using current time", __func__);
> + clock_gettime(CLOCK_REALTIME_COARSE, &ts);
> + }
> + pthread_mutex_lock(×tamp_mutex);
> + bindings_last_updated = ts;
> + pthread_mutex_unlock(×tamp_mutex);
> + } else if (ret == -1 && can_write && !conf->bindings_read_only) {
> + ret = update_bindings_file(bindings, conf->bindings_file);
> + if (ret == 0)
> + rc = BINDINGS_FILE_READ;
> + else
> + rc = BINDINGS_FILE_BAD;
> + } else {
> + condlog(0, "ERROR: bad settings in read-only bindings file %s",
> + conf->bindings_file);
> + rc = BINDINGS_FILE_BAD;
> + }
> + pthread_cleanup_pop(1);
> + } else {
> + condlog(1, "failed to fdopen %s: %m",
> + conf->bindings_file);
> + close(fd);
> + rc = BINDINGS_FILE_ERROR;
> + }
> +
> + return rc;
> +}
> +
> /*
> * check_alias_settings(): test for inconsistent alias configuration
> *
> @@ -661,8 +851,7 @@ static int mp_alias_compar(const void *p1, const void *p2)
> */
> int check_alias_settings(const struct config *conf)
> {
> - int can_write;
> - int rc = 0, i, fd;
> + int i, rc;
> Bindings bindings = {.allocated = 0, };
> vector mptable = NULL;
> struct mpentry *mpe;
> @@ -695,27 +884,12 @@ int check_alias_settings(const struct config *conf)
> pthread_cleanup_pop(1);
> pthread_cleanup_pop(1);
>
> - fd = open_file(conf->bindings_file, &can_write, BINDINGS_FILE_HEADER);
> - if (fd != -1) {
> - FILE *file = fdopen(fd, "r");
> + rc = _read_bindings_file(conf, &bindings, true);
>
> - if (file != NULL) {
> - pthread_cleanup_push(cleanup_fclose, file);
> - rc = _check_bindings_file(conf, file, &bindings);
> - pthread_cleanup_pop(1);
> - if (rc == -1 && can_write && !conf->bindings_read_only)
> - rc = update_bindings_file(&bindings, conf->bindings_file);
> - else if (rc == -1)
> - condlog(0, "ERROR: bad settings in read-only bindings file %s",
> - conf->bindings_file);
> - } else {
> - condlog(1, "failed to fdopen %s: %m",
> - conf->bindings_file);
> - close(fd);
> - }
> + if (rc == BINDINGS_FILE_READ) {
> + set_global_bindings(&bindings);
> + rc = 0;
> }
>
> - cleanup_bindings();
> - global_bindings = bindings;
> return rc;
> }
> diff --git a/libmultipath/alias.h b/libmultipath/alias.h
> index 5ef6720..ca8911f 100644
> --- a/libmultipath/alias.h
> +++ b/libmultipath/alias.h
> @@ -10,5 +10,6 @@ char *get_user_friendly_alias(const char *wwid, const char *file,
> struct config;
> int check_alias_settings(const struct config *);
> void cleanup_bindings(void);
> -
> +struct inotify_event;
> +void handle_bindings_file_inotify(const struct inotify_event *event);
> #endif /* _ALIAS_H */
> diff --git a/libmultipath/libmultipath.version b/libmultipath/libmultipath.version
> index ddd302f..57e50c1 100644
> --- a/libmultipath/libmultipath.version
> +++ b/libmultipath/libmultipath.version
> @@ -238,3 +238,8 @@ global:
> local:
> *;
> };
> +
> +LIBMULTIPATH_20.1.0 {
> +global:
> + handle_bindings_file_inotify;
> +};
> diff --git a/multipathd/uxlsnr.c b/multipathd/uxlsnr.c
> index 02e89fb..d1f8f23 100644
> --- a/multipathd/uxlsnr.c
> +++ b/multipathd/uxlsnr.c
> @@ -41,6 +41,7 @@
> #include "cli.h"
> #include "uxlsnr.h"
> #include "strbuf.h"
> +#include "alias.h"
>
> /* state of client connection */
> enum {
> @@ -190,6 +191,7 @@ void wakeup_cleanup(void *arg)
> struct watch_descriptors {
> int conf_wd;
> int dir_wd;
> + int mp_wd; /* /etc/multipath; for bindings file */
> };
>
> /* failing to set the watch descriptor is o.k. we just miss a warning
> @@ -200,6 +202,8 @@ static void reset_watch(int notify_fd, struct watch_descriptors *wds,
> struct config *conf;
> int dir_reset = 0;
> int conf_reset = 0;
> + int mp_reset = 0;
> + char *bindings_file __attribute__((cleanup(cleanup_charp))) = NULL;
>
> if (notify_fd == -1)
> return;
> @@ -214,7 +218,10 @@ static void reset_watch(int notify_fd, struct watch_descriptors *wds,
> conf_reset = 1;
> if (wds->dir_wd == -1)
> dir_reset = 1;
> + if (wds->mp_wd == -1)
> + mp_reset = 1;
> }
> + bindings_file = strdup(conf->bindings_file);
> put_multipath_config(conf);
>
> if (dir_reset) {
> @@ -235,7 +242,18 @@ static void reset_watch(int notify_fd, struct watch_descriptors *wds,
> if (wds->conf_wd == -1)
> condlog(3, "didn't set up notifications on /etc/multipath.conf: %m");
> }
> - return;
> + if (mp_reset && bindings_file) {
> + char *slash = strrchr(bindings_file, '/');
> +
> + if (slash && slash > bindings_file) {
> + *slash = '\0';
> + wds->mp_wd = inotify_add_watch(notify_fd, bindings_file,
> + IN_MOVED_TO|IN_ONLYDIR);
> + if (wds->mp_wd == -1)
> + condlog(3, "didn't set up notifications on %s: %m",
> + bindings_file);
> + }
> + }
> }
>
> static void handle_inotify(int fd, struct watch_descriptors *wds)
> @@ -256,12 +274,13 @@ static void handle_inotify(int fd, struct watch_descriptors *wds)
> inotify_rm_watch(fd, wds->conf_wd);
> if (wds->dir_wd != -1)
> inotify_rm_watch(fd, wds->dir_wd);
> - wds->conf_wd = wds->dir_wd = -1;
> + if (wds->mp_wd != -1)
> + inotify_rm_watch(fd, wds->mp_wd);
> + wds->conf_wd = wds->dir_wd = wds->mp_wd = -1;
> }
> break;
> }
>
> - got_notify = 1;
> for (ptr = buff; ptr < buff + len;
> ptr += sizeof(struct inotify_event) + event->len) {
> event = (const struct inotify_event *) ptr;
> @@ -273,7 +292,13 @@ static void handle_inotify(int fd, struct watch_descriptors *wds)
> wds->conf_wd = inotify_add_watch(notify_fd, DEFAULT_CONFIGFILE, IN_CLOSE_WRITE);
> else if (wds->dir_wd == event->wd)
> wds->dir_wd = -1;
> + else if (wds->mp_wd == event->wd)
> + wds->mp_wd = -1;
> }
> + if (wds->mp_wd != -1 && wds->mp_wd == event->wd)
> + handle_bindings_file_inotify(event);
> + else
> + got_notify = 1;
> }
> }
> if (got_notify)
> @@ -599,7 +624,7 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
> int max_pfds = MIN_POLLS + POLLFDS_BASE;
> /* conf->sequence_nr will be 1 when uxsock_listen is first called */
> unsigned int sequence_nr = 0;
> - struct watch_descriptors wds = { .conf_wd = -1, .dir_wd = -1 };
> + struct watch_descriptors wds = { .conf_wd = -1, .dir_wd = -1, .mp_wd = -1, };
> struct vectors *vecs = trigger_data;
>
> condlog(3, "uxsock: startup listener");
> @@ -666,7 +691,8 @@ void *uxsock_listen(long ux_sock, void *trigger_data)
>
> reset_watch(notify_fd, &wds, &sequence_nr);
> polls[POLLFD_NOTIFY].fd = notify_fd;
> - if (notify_fd == -1 || (wds.conf_wd == -1 && wds.dir_wd == -1))
> + if (notify_fd == -1 || (wds.conf_wd == -1 && wds.dir_wd == -1
> + && wds.mp_wd == -1))
> polls[POLLFD_NOTIFY].events = 0;
> else
> polls[POLLFD_NOTIFY].events = POLLIN;
> diff --git a/tests/alias.c b/tests/alias.c
> index 4d0adba..d41d396 100644
> --- a/tests/alias.c
> +++ b/tests/alias.c
> @@ -1954,6 +1954,9 @@ int main(void)
> int ret = 0;
> init_test_verbosity(3);
>
> + /* avoid open_file() call in _read_bindings_file */
> + bindings_file_changed = 0;
> +
> ret += test_format_devname();
> ret += test_scan_devname();
> ret += test_lookup_binding();
> --
> 2.42.0
--
dm-devel mailing list
dm-devel@xxxxxxxxxx
https://listman.redhat.com/mailman/listinfo/dm-devel
