mdmon: already read sysfs files once after opening.

seq_file in the kernel will allocate a read buffer on
first read.  We want this to happen under the managemon thread,
not the 'monitor' thread, as the latter is not allow to allocate
memory (might deadlock).
So do a first read after opening.

Signed-off-by: NeilBrown <neilb@suse.de>

diff --git a/managemon.c b/managemon.c
index 1c9eccc4c49077095e489ffa4ec32f1089f0120f..9b14d1ec3d6a60c68507ef860e6e91f43c7f5d8e 100644 (file)
--- a/managemon.c
+++ b/managemon.c
@@ -402,6 +402,20 @@ static void manage_container(struct mdstat_ent *mdstat,
        }
 }
 
+static int sysfs_open2(char *devnum, char *name, char *attr)
+{
+       int fd = sysfs_open(devnum, name, attr);
+       if (fd >= 0) {
+               /* seq_file in the kernel allocates buffer space
+                * on the first read.  Do that now so 'monitor'
+                * never needs too.
+                */
+               char buf[200];
+               read(fd, buf, sizeof(buf));
+       }
+       return fd;
+}
+
 static int disk_init_and_add(struct mdinfo *disk, struct mdinfo *clone,
                             struct active_array *aa)
 {
@@ -409,10 +423,11 @@ static int disk_init_and_add(struct mdinfo *disk, struct mdinfo *clone,
                return -1;
 
        *disk = *clone;
-       disk->recovery_fd = sysfs_open(aa->info.sys_name, disk->sys_name, "recovery_start");
+       disk->recovery_fd = sysfs_open2(aa->info.sys_name, disk->sys_name,
+                                       "recovery_start");
        if (disk->recovery_fd < 0)
                return -1;
-       disk->state_fd = sysfs_open(aa->info.sys_name, disk->sys_name, "state");
+       disk->state_fd = sysfs_open2(aa->info.sys_name, disk->sys_name, "state");
        if (disk->state_fd < 0) {
                close(disk->recovery_fd);
                return -1;
@@ -692,11 +707,12 @@ static void manage_new(struct mdstat_ent *mdstat,
                }
        }
 
-       new->action_fd = sysfs_open(new->info.sys_name, NULL, "sync_action");
-       new->info.state_fd = sysfs_open(new->info.sys_name, NULL, "array_state");
-       new->resync_start_fd = sysfs_open(new->info.sys_name, NULL, "resync_start");
-       new->metadata_fd = sysfs_open(new->info.sys_name, NULL, "metadata_version");
-       new->sync_completed_fd = sysfs_open(new->info.sys_name, NULL, "sync_completed");
+       new->action_fd = sysfs_open2(new->info.sys_name, NULL, "sync_action");
+       new->info.state_fd = sysfs_open2(new->info.sys_name, NULL, "array_state");
+       new->resync_start_fd = sysfs_open2(new->info.sys_name, NULL, "resync_start");
+       new->metadata_fd = sysfs_open2(new->info.sys_name, NULL, "metadata_version");
+       new->sync_completed_fd = sysfs_open2(new->info.sys_name, NULL, "sync_completed");
+
        dprintf("%s: inst: %s action: %d state: %d\n", __func__, inst,
                new->action_fd, new->info.state_fd);