libmount: (monitor) optimize inotify utab watch

Don't repeat no-op inotify_add_watch() calls. This happens when we
monitor the /run[/mount] directory before the utab.event file exists.
The old version just tries to create a watch and ignores ENOENT
errors. It seems better to remember the path of the last created watch
and not repeat it.

Signed-off-by: Karel Zak <kzak@redhat.com>

diff --git a/libmount/src/monitor_utab.c b/libmount/src/monitor_utab.c
index 1b5815b4d68cfd7ee10c41fdf567967e9371c2fb..f0e90c204792620d80bd2abd8a24389ded9f82ed 100644 (file)
--- a/libmount/src/monitor_utab.c
+++ b/libmount/src/monitor_utab.c
@@ -17,10 +17,31 @@
 #include "monitor.h"
 
 #include "fileutils.h"
+#include "strutils.h"
 
 #include <sys/inotify.h>
 #include <sys/epoll.h>
 
+/* private monitor data */
+struct monitor_entrydata {
+       char    *path;          /* monitored path (dir or final event file) */
+};
+
+static int userspace_free_data(struct monitor_entry *me)
+{
+       struct monitor_entrydata *data;
+
+       if (!me || !me->data)
+               return 0;
+
+       data = (struct monitor_entrydata *) me->data;
+
+       free(data->path);
+       free(me->data);
+       me->data = NULL;
+       return 0;
+}
+
 static int userspace_monitor_close_fd(
                        struct libmnt_monitor *mn __attribute__((__unused__)),
                        struct monitor_entry *me)
@@ -35,15 +56,37 @@ static int userspace_monitor_close_fd(
 
 static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
 {
+       struct monitor_entrydata *data = NULL;
        char *filename = NULL;
+       const char *p;
        int wd, rc = -EINVAL;
 
        assert(me);
        assert(me->path);
 
-       /*
-        * libmount uses utab.event file to monitor and control utab updates
+       if (fd)
+               *fd = -1;
+
+       data = (struct monitor_entrydata *) me->data;
+       if (!data) {
+               me->data = data = calloc(1, sizeof(*data));
+               if (!data) {
+                       rc = -ENOMEM;
+                       goto done;
+               }
+       }
+
+       /* The inotify buffer may contain obsolete events from when
+        * we have not yet monitored the final event file; don't
+        * call inotify_add_watch() if already monitoring the final file.
         */
+       if (data->path && (p = ul_startswith(data->path, me->path))
+           && strcmp(p, ".event") == 0) {
+               rc = 0;
+               goto done;
+       }
+
+       /* libmount uses utab.event file to monitor and control utab updates */
        if (asprintf(&filename, "%s.event", me->path) <= 0) {
                rc = -ENOMEM;
                goto done;
@@ -59,18 +102,29 @@ static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
                        *final = 0;     /* success */
                if (fd)
                        *fd = wd;
-               goto done;
+               goto remember;
        } else if (errno != ENOENT) {
                rc = -errno;
                goto done;
        }
 
+       data = (struct monitor_entrydata *) me->data;
+
        while (strchr(filename, '/')) {
+               /*
+                * Try watching the directory when we expect the final event file. If the
+                * directory does not exist, then try the parent directory, and so on. Remember
+                * the last created watch path to avoid unnecessary inotify_add_watch() calls.
+                */
                stripoff_last_component(filename);
                if (!*filename)
                        break;
 
                /* try directory where is the event file */
+               if (data->path && strcmp(data->path, filename) == 0) {
+                       rc = 0;
+                       break;  /* already exist */
+               }
                errno = 0;
                wd = inotify_add_watch(me->fd, filename, IN_CREATE|IN_ISDIR);
                if (wd >= 0) {
@@ -78,7 +132,7 @@ static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
                        rc = 0;
                        if (fd)
                                *fd = wd;
-                       break;
+                       goto remember;
                }
 
                if (errno != ENOENT) {
@@ -89,6 +143,10 @@ static int userspace_add_watch(struct monitor_entry *me, int *final, int *fd)
 done:
        free(filename);
        return rc;
+remember:
+       free(data->path);
+       data->path = filename;
+       return rc;
 }
 
 static int userspace_monitor_get_fd(struct libmnt_monitor *mn,
@@ -129,7 +187,7 @@ err:
 static int userspace_process_event(struct libmnt_monitor *mn,
                                        struct monitor_entry *me)
 {
-       char buf[sizeof(struct inotify_event) + NAME_MAX + 1];
+       char buf[16 * (sizeof(struct inotify_event) + NAME_MAX + 1)];
        int status = 1;         /* nothing by default */
 
        if (!me || me->fd < 0)
@@ -161,7 +219,7 @@ static int userspace_process_event(struct libmnt_monitor *mn,
                                /* add watch for the event file */
                                userspace_add_watch(me, &status, &fd);
 
-                               if (fd != e->wd) {
+                               if (fd >= 0 && fd != e->wd) {
                                        DBG(MONITOR, ul_debugobj(mn, " removing watch [fd=%d]", e->wd));
                                        inotify_rm_watch(me->fd, e->wd);
                                }
@@ -180,6 +238,7 @@ static int userspace_process_event(struct libmnt_monitor *mn,
 static const struct monitor_opers userspace_opers = {
        .op_get_fd              = userspace_monitor_get_fd,
        .op_close_fd            = userspace_monitor_close_fd,
+       .op_free_data           = userspace_free_data,
        .op_process_event       = userspace_process_event
 };