implement in-kernel gendisk events handling

Currently, media presence polling for removeable block devices is done
from userland.  There are several issues with this.

* Polling is done by periodically opening the device.  For SCSI
  devices, the command sequence generated by such action involves a
  few different commands including TEST_UNIT_READY.  This behavior,
  while perfectly legal, is different from Windows which only issues
  single command, GET_EVENT_STATUS_NOTIFICATION.  Unfortunately, some
  ATAPI devices lock up after being periodically queried such command
  sequences.

* There is no reliable and unintrusive way for a userland program to
  tell whether the target device is safe for media presence polling.
  For example, polling for media presence during an on-going burning
  session can make it fail.  The polling program can avoid this by
  opening the device with O_EXCL but then it risks making a valid
  exclusive user of the device fail w/ -EBUSY.

* Userland polling is unnecessarily heavy and in-kernel implementation
  is lighter and better coordinated (workqueue, timer slack).

This patch implements framework for in-kernel disk event handling,
which includes media presence polling.

* bdops->check_events() is added, which supercedes ->media_changed().
  It should check whether there's any pending event and return if so.
  Currently, two events are defined - DISK_EVENT_MEDIA_CHANGE and
  DISK_EVENT_EJECT_REQUEST.  ->check_events() is guaranteed not to be
  called parallelly.

* gendisk->events and ->async_events are added.  These should be
  initialized by block driver before passing the device to add_disk().
  The former contains the mask of all supported events and the latter
  the mask of all events which the device can report without polling.
  /sys/block/*/events[_async] export these to userland.

* Kernel parameter block.events_dfl_poll_msecs controls the system
  polling interval (default is 0 which means disable) and
  /sys/block/*/events_poll_msecs control polling intervals for
  individual devices (default is -1 meaning use system setting).  Note
  that if a device can report all supported events asynchronously and
  its polling interval isn't explicitly set, the device won't be
  polled regardless of the system polling interval.

* If a device is opened exclusively with write access, event checking
  is automatically disabled until all write exclusive accesses are
  released.

* There are event 'clearing' events.  For example, both of currently
  defined events are cleared after the device has been successfully
  opened.  This information is passed to ->check_events() callback
  using @clearing argument as a hint.

* Event checking is always performed from system_nrt_wq and timer
  slack is set to 25% for polling.

* Nothing changes for drivers which implement ->media_changed() but
  not ->check_events().  Going forward, all drivers will be converted
  to ->check_events() and ->media_change() will be dropped.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kay Sievers <kay.sievers@vrfy.org>
Cc: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

1 files changed, 429 insertions, 0 deletions

diff --git a/block/genhd.c b/block/genhd.c
index 2e5e4c0a1133..5465a824d489 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -18,6 +18,7 @@
 #include <linux/buffer_head.h>
 #include <linux/mutex.h>
 #include <linux/idr.h>
+#include <linux/log2.h>
 
 #include "blk.h"
 
@@ -35,6 +36,10 @@ static DEFINE_IDR(ext_devt_idr);
 
 static struct device_type disk_type;
 
+static void disk_add_events(struct gendisk *disk);
+static void disk_del_events(struct gendisk *disk);
+static void disk_release_events(struct gendisk *disk);
+
 /**
  * disk_get_part - get partition
  * @disk: disk to look partition from
@@ -609,6 +614,8 @@ void add_disk(struct gendisk *disk)
         retval = sysfs_create_link(&disk_to_dev(disk)->kobj, &bdi->dev->kobj,
                                    "bdi");
         WARN_ON(retval);
+
+        disk_add_events(disk);
 }
 EXPORT_SYMBOL(add_disk);
 
@@ -617,6 +624,8 @@ void del_gendisk(struct gendisk *disk)
         struct disk_part_iter piter;
         struct hd_struct *part;
 
+        disk_del_events(disk);
+
         /* invalidate stuff */
         disk_part_iter_init(&piter, disk,
                              DISK_PITER_INCL_EMPTY | DISK_PITER_REVERSE);
@@ -1089,6 +1098,7 @@ static void disk_release(struct device *dev)
 {
         struct gendisk *disk = dev_to_disk(dev);
 
+        disk_release_events(disk);
         kfree(disk->random);
         disk_replace_part_tbl(disk, NULL);
         free_part_stats(&disk->part0);
@@ -1350,3 +1360,422 @@ int invalidate_partition(struct gendisk *disk, int partno)
 }
 
 EXPORT_SYMBOL(invalidate_partition);
+
+/*
+ * Disk events - monitor disk events like media change and eject request.
+ */
+struct disk_events {
+        struct list_head        node;           /* all disk_event's */
+        struct gendisk          *disk;          /* the associated disk */
+        spinlock_t              lock;
+
+        int                     block;          /* event blocking depth */
+        unsigned int            pending;        /* events already sent out */
+        unsigned int            clearing;       /* events being cleared */
+
+        long                    poll_msecs;     /* interval, -1 for default */
+        struct delayed_work     dwork;
+};
+
+static const char *disk_events_strs[] = {
+        [ilog2(DISK_EVENT_MEDIA_CHANGE)]        = "media_change",
+        [ilog2(DISK_EVENT_EJECT_REQUEST)]       = "eject_request",
+};
+
+static char *disk_uevents[] = {
+        [ilog2(DISK_EVENT_MEDIA_CHANGE)]        = "DISK_MEDIA_CHANGE=1",
+        [ilog2(DISK_EVENT_EJECT_REQUEST)]       = "DISK_EJECT_REQUEST=1",
+};
+
+/* list of all disk_events */
+static DEFINE_MUTEX(disk_events_mutex);
+static LIST_HEAD(disk_events);
+
+/* disable in-kernel polling by default */
+static unsigned long disk_events_dfl_poll_msecs = 0;
+
+static unsigned long disk_events_poll_jiffies(struct gendisk *disk)
+{
+        struct disk_events *ev = disk->ev;
+        long intv_msecs = 0;
+
+        /*
+         * If device-specific poll interval is set, always use it.  If
+         * the default is being used, poll iff there are events which
+         * can't be monitored asynchronously.
+         */
+        if (ev->poll_msecs >= 0)
+                intv_msecs = ev->poll_msecs;
+        else if (disk->events & ~disk->async_events)
+                intv_msecs = disk_events_dfl_poll_msecs;
+
+        return msecs_to_jiffies(intv_msecs);
+}
+
+static void __disk_block_events(struct gendisk *disk, bool sync)
+{
+        struct disk_events *ev = disk->ev;
+        unsigned long flags;
+        bool cancel;
+
+        spin_lock_irqsave(&ev->lock, flags);
+        cancel = !ev->block++;
+        spin_unlock_irqrestore(&ev->lock, flags);
+
+        if (cancel) {
+                if (sync)
+                        cancel_delayed_work_sync(&disk->ev->dwork);
+                else
+                        cancel_delayed_work(&disk->ev->dwork);
+        }
+}
+
+static void __disk_unblock_events(struct gendisk *disk, bool check_now)
+{
+        struct disk_events *ev = disk->ev;
+        unsigned long intv;
+        unsigned long flags;
+
+        spin_lock_irqsave(&ev->lock, flags);
+
+        if (WARN_ON_ONCE(ev->block <= 0))
+                goto out_unlock;
+
+        if (--ev->block)
+                goto out_unlock;
+
+        /*
+         * Not exactly a latency critical operation, set poll timer
+         * slack to 25% and kick event check.
+         */
+        intv = disk_events_poll_jiffies(disk);
+        set_timer_slack(&ev->dwork.timer, intv / 4);
+        if (check_now)
+                queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
+        else if (intv)
+                queue_delayed_work(system_nrt_wq, &ev->dwork, intv);
+out_unlock:
+        spin_unlock_irqrestore(&ev->lock, flags);
+}
+
+/**
+ * disk_block_events - block and flush disk event checking
+ * @disk: disk to block events for
+ *
+ * On return from this function, it is guaranteed that event checking
+ * isn't in progress and won't happen until unblocked by
+ * disk_unblock_events().  Events blocking is counted and the actual
+ * unblocking happens after the matching number of unblocks are done.
+ *
+ * Note that this intentionally does not block event checking from
+ * disk_clear_events().
+ *
+ * CONTEXT:
+ * Might sleep.
+ */
+void disk_block_events(struct gendisk *disk)
+{
+        if (disk->ev)
+                __disk_block_events(disk, true);
+}
+
+/**
+ * disk_unblock_events - unblock disk event checking
+ * @disk: disk to unblock events for
+ *
+ * Undo disk_block_events().  When the block count reaches zero, it
+ * starts events polling if configured.
+ *
+ * CONTEXT:
+ * Don't care.  Safe to call from irq context.
+ */
+void disk_unblock_events(struct gendisk *disk)
+{
+        if (disk->ev)
+                __disk_unblock_events(disk, true);
+}
+
+/**
+ * disk_check_events - schedule immediate event checking
+ * @disk: disk to check events for
+ *
+ * Schedule immediate event checking on @disk if not blocked.
+ *
+ * CONTEXT:
+ * Don't care.  Safe to call from irq context.
+ */
+void disk_check_events(struct gendisk *disk)
+{
+        if (disk->ev) {
+                __disk_block_events(disk, false);
+                __disk_unblock_events(disk, true);
+        }
+}
+EXPORT_SYMBOL_GPL(disk_check_events);
+
+/**
+ * disk_clear_events - synchronously check, clear and return pending events
+ * @disk: disk to fetch and clear events from
+ * @mask: mask of events to be fetched and clearted
+ *
+ * Disk events are synchronously checked and pending events in @mask
+ * are cleared and returned.  This ignores the block count.
+ *
+ * CONTEXT:
+ * Might sleep.
+ */
+unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask)
+{
+        const struct block_device_operations *bdops = disk->fops;
+        struct disk_events *ev = disk->ev;
+        unsigned int pending;
+
+        if (!ev) {
+                /* for drivers still using the old ->media_changed method */
+                if ((mask & DISK_EVENT_MEDIA_CHANGE) &&
+                    bdops->media_changed && bdops->media_changed(disk))
+                        return DISK_EVENT_MEDIA_CHANGE;
+                return 0;
+        }
+
+        /* tell the workfn about the events being cleared */
+        spin_lock_irq(&ev->lock);
+        ev->clearing |= mask;
+        spin_unlock_irq(&ev->lock);
+
+        /* uncondtionally schedule event check and wait for it to finish */
+        __disk_block_events(disk, true);
+        queue_delayed_work(system_nrt_wq, &ev->dwork, 0);
+        flush_delayed_work(&ev->dwork);
+        __disk_unblock_events(disk, false);
+
+        /* then, fetch and clear pending events */
+        spin_lock_irq(&ev->lock);
+        WARN_ON_ONCE(ev->clearing & mask);      /* cleared by workfn */
+        pending = ev->pending & mask;
+        ev->pending &= ~mask;
+        spin_unlock_irq(&ev->lock);
+
+        return pending;
+}
+
+static void disk_events_workfn(struct work_struct *work)
+{
+        struct delayed_work *dwork = to_delayed_work(work);
+        struct disk_events *ev = container_of(dwork, struct disk_events, dwork);
+        struct gendisk *disk = ev->disk;
+        char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };
+        unsigned int clearing = ev->clearing;
+        unsigned int events;
+        unsigned long intv;
+        int nr_events = 0, i;
+
+        /* check events */
+        events = disk->fops->check_events(disk, clearing);
+
+        /* accumulate pending events and schedule next poll if necessary */
+        spin_lock_irq(&ev->lock);
+
+        events &= ~ev->pending;
+        ev->pending |= events;
+        ev->clearing &= ~clearing;
+
+        intv = disk_events_poll_jiffies(disk);
+        if (!ev->block && intv)
+                queue_delayed_work(system_nrt_wq, &ev->dwork, intv);
+
+        spin_unlock_irq(&ev->lock);
+
+        /* tell userland about new events */
+        for (i = 0; i < ARRAY_SIZE(disk_uevents); i++)
+                if (events & (1 << i))
+                        envp[nr_events++] = disk_uevents[i];
+
+        if (nr_events)
+                kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
+}
+
+/*
+ * A disk events enabled device has the following sysfs nodes under
+ * its /sys/block/X/ directory.
+ *
+ * events               : list of all supported events
+ * events_async         : list of events which can be detected w/o polling
+ * events_poll_msecs    : polling interval, 0: disable, -1: system default
+ */
+static ssize_t __disk_events_show(unsigned int events, char *buf)
+{
+        const char *delim = "";
+        ssize_t pos = 0;
+        int i;
+
+        for (i = 0; i < ARRAY_SIZE(disk_events_strs); i++)
+                if (events & (1 << i)) {
+                        pos += sprintf(buf + pos, "%s%s",
+                                       delim, disk_events_strs[i]);
+                        delim = " ";
+                }
+        if (pos)
+                pos += sprintf(buf + pos, "\n");
+        return pos;
+}
+
+static ssize_t disk_events_show(struct device *dev,
+                                struct device_attribute *attr, char *buf)
+{
+        struct gendisk *disk = dev_to_disk(dev);
+
+        return __disk_events_show(disk->events, buf);
+}
+
+static ssize_t disk_events_async_show(struct device *dev,
+                                      struct device_attribute *attr, char *buf)
+{
+        struct gendisk *disk = dev_to_disk(dev);
+
+        return __disk_events_show(disk->async_events, buf);
+}
+
+static ssize_t disk_events_poll_msecs_show(struct device *dev,
+                                           struct device_attribute *attr,
+                                           char *buf)
+{
+        struct gendisk *disk = dev_to_disk(dev);
+
+        return sprintf(buf, "%ld\n", disk->ev->poll_msecs);
+}
+
+static ssize_t disk_events_poll_msecs_store(struct device *dev,
+                                            struct device_attribute *attr,
+                                            const char *buf, size_t count)
+{
+        struct gendisk *disk = dev_to_disk(dev);
+        long intv;
+
+        if (!count || !sscanf(buf, "%ld", &intv))
+                return -EINVAL;
+
+        if (intv < 0 && intv != -1)
+                return -EINVAL;
+
+        __disk_block_events(disk, true);
+        disk->ev->poll_msecs = intv;
+        __disk_unblock_events(disk, true);
+
+        return count;
+}
+
+static const DEVICE_ATTR(events, S_IRUGO, disk_events_show, NULL);
+static const DEVICE_ATTR(events_async, S_IRUGO, disk_events_async_show, NULL);
+static const DEVICE_ATTR(events_poll_msecs, S_IRUGO|S_IWUSR,
+                         disk_events_poll_msecs_show,
+                         disk_events_poll_msecs_store);
+
+static const struct attribute *disk_events_attrs[] = {
+        &dev_attr_events.attr,
+        &dev_attr_events_async.attr,
+        &dev_attr_events_poll_msecs.attr,
+        NULL,
+};
+
+/*
+ * The default polling interval can be specified by the kernel
+ * parameter block.events_dfl_poll_msecs which defaults to 0
+ * (disable).  This can also be modified runtime by writing to
+ * /sys/module/block/events_dfl_poll_msecs.
+ */
+static int disk_events_set_dfl_poll_msecs(const char *val,
+                                          const struct kernel_param *kp)
+{
+        struct disk_events *ev;
+        int ret;
+
+        ret = param_set_ulong(val, kp);
+        if (ret < 0)
+                return ret;
+
+        mutex_lock(&disk_events_mutex);
+
+        list_for_each_entry(ev, &disk_events, node)
+                disk_check_events(ev->disk);
+
+        mutex_unlock(&disk_events_mutex);
+
+        return 0;
+}
+
+static const struct kernel_param_ops disk_events_dfl_poll_msecs_param_ops = {
+        .set    = disk_events_set_dfl_poll_msecs,
+        .get    = param_get_ulong,
+};
+
+#undef MODULE_PARAM_PREFIX
+#define MODULE_PARAM_PREFIX     "block."
+
+module_param_cb(events_dfl_poll_msecs, &disk_events_dfl_poll_msecs_param_ops,
+                &disk_events_dfl_poll_msecs, 0644);
+
+/*
+ * disk_{add|del|release}_events - initialize and destroy disk_events.
+ */
+static void disk_add_events(struct gendisk *disk)
+{
+        struct disk_events *ev;
+
+        if (!disk->fops->check_events || !(disk->events | disk->async_events))
+                return;
+
+        ev = kzalloc(sizeof(*ev), GFP_KERNEL);
+        if (!ev) {
+                pr_warn("%s: failed to initialize events\n", disk->disk_name);
+                return;
+        }
+
+        if (sysfs_create_files(&disk_to_dev(disk)->kobj,
+                               disk_events_attrs) < 0) {
+                pr_warn("%s: failed to create sysfs files for events\n",
+                        disk->disk_name);
+                kfree(ev);
+                return;
+        }
+
+        disk->ev = ev;
+
+        INIT_LIST_HEAD(&ev->node);
+        ev->disk = disk;
+        spin_lock_init(&ev->lock);
+        ev->block = 1;
+        ev->poll_msecs = -1;
+        INIT_DELAYED_WORK(&ev->dwork, disk_events_workfn);
+
+        mutex_lock(&disk_events_mutex);
+        list_add_tail(&ev->node, &disk_events);
+        mutex_unlock(&disk_events_mutex);
+
+        /*
+         * Block count is initialized to 1 and the following initial
+         * unblock kicks it into action.
+         */
+        __disk_unblock_events(disk, true);
+}
+
+static void disk_del_events(struct gendisk *disk)
+{
+        if (!disk->ev)
+                return;
+
+        __disk_block_events(disk, true);
+
+        mutex_lock(&disk_events_mutex);
+        list_del_init(&disk->ev->node);
+        mutex_unlock(&disk_events_mutex);
+
+        sysfs_remove_files(&disk_to_dev(disk)->kobj, disk_events_attrs);
+}
+
+static void disk_release_events(struct gendisk *disk)
+{
+        /* the block count should be 1 from disk_del_events() */
+        WARN_ON_ONCE(disk->ev && disk->ev->block != 1);
+        kfree(disk->ev);
+}