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@xxxxxxxxxx>
Cc: Kay Sievers <kay.sievers@xxxxxxxx>
Cc: Jan Kara <jack@xxxxxxx>
---
block/genhd.c | 429 ++++++++++++++++++++++++++++++++++++++++++++++++
fs/block_dev.c | 41 ++++-
include/linux/blkdev.h | 3 +
include/linux/fs.h | 1 +
include/linux/genhd.h | 18 ++-
5 files changed, 484 insertions(+), 8 deletions(-)
diff --git a/block/genhd.c b/block/genhd.c
index 2e5e4c0..5465a82 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);
+}
diff --git a/fs/block_dev.c b/fs/block_dev.c
index c1c1b8c..6017389 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -948,10 +948,11 @@ int check_disk_change(struct block_device *bdev)
{
struct gendisk *disk = bdev->bd_disk;
const struct block_device_operations *bdops = disk->fops;
+ unsigned int events;
- if (!bdops->media_changed)
- return 0;
- if (!bdops->media_changed(bdev->bd_disk))
+ events = disk_clear_events(disk, DISK_EVENT_MEDIA_CHANGE |
+ DISK_EVENT_EJECT_REQUEST);
+ if (!(events & DISK_EVENT_MEDIA_CHANGE))
return 0;
flush_disk(bdev);
@@ -1158,9 +1159,10 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
if (whole) {
/* finish claiming */
+ mutex_lock(&bdev->bd_mutex);
spin_lock(&bdev_lock);
- if (res == 0) {
+ if (!res) {
BUG_ON(!bd_may_claim(bdev, whole, holder));
/*
* Note that for a whole device bd_holders
@@ -1180,6 +1182,20 @@ int blkdev_get(struct block_device *bdev, fmode_t mode, void *holder)
wake_up_bit(&whole->bd_claiming, 0);
spin_unlock(&bdev_lock);
+
+ /*
+ * Block event polling for write claims. Any write
+ * holder makes the write_holder state stick until all
+ * are released. This is good enough and tracking
+ * individual writeable reference is too fragile given
+ * the way @mode is used in blkdev_get/put().
+ */
+ if (!res && (mode & FMODE_WRITE) && !bdev->bd_write_holder) {
+ bdev->bd_write_holder = true;
+ disk_block_events(bdev->bd_disk);
+ }
+
+ mutex_unlock(&bdev->bd_mutex);
bdput(whole);
}
@@ -1353,12 +1369,23 @@ int blkdev_put(struct block_device *bdev, fmode_t mode)
spin_unlock(&bdev_lock);
- /* if this was the last claim, holder link should go too */
- if (bdev_free)
+ /*
+ * If this was the last claim, remove holder link and
+ * unblock evpoll if it was a write holder.
+ */
+ if (bdev_free) {
bd_unlink_disk_holder(bdev);
+ if (bdev->bd_write_holder) {
+ disk_unblock_events(bdev->bd_disk);
+ bdev->bd_write_holder = false;
+ } else
+ disk_check_events(bdev->bd_disk);
+ }
mutex_unlock(&bdev->bd_mutex);
- }
+ } else
+ disk_check_events(bdev->bd_disk);
+
return __blkdev_put(bdev, mode, 0);
}
EXPORT_SYMBOL(blkdev_put);
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 83031bc..05667e6 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1251,6 +1251,9 @@ struct block_device_operations {
int (*compat_ioctl) (struct block_device *, fmode_t, unsigned, unsigned long);
int (*direct_access) (struct block_device *, sector_t,
void **, unsigned long *);
+ unsigned int (*check_events) (struct gendisk *disk,
+ unsigned int clearing);
+ /* ->media_changed() is DEPRECATED, use ->check_events() instead */
int (*media_changed) (struct gendisk *);
void (*unlock_native_capacity) (struct gendisk *);
int (*revalidate_disk) (struct gendisk *);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index f485015..997d22e 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -662,6 +662,7 @@ struct block_device {
void * bd_claiming;
void * bd_holder;
int bd_holders;
+ bool bd_write_holder;
#ifdef CONFIG_SYSFS
struct gendisk * bd_holder_disk; /* for sysfs slave linkng */
#endif
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 56e17ed..13893aa 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -127,6 +127,11 @@ struct hd_struct {
#define GENHD_FL_EXT_DEVT 64 /* allow extended devt */
#define GENHD_FL_NATIVE_CAPACITY 128
+enum {
+ DISK_EVENT_MEDIA_CHANGE = 1 << 0, /* media changed */
+ DISK_EVENT_EJECT_REQUEST = 1 << 1, /* eject requested */
+};
+
#define BLK_SCSI_MAX_CMDS (256)
#define BLK_SCSI_CMD_PER_LONG (BLK_SCSI_MAX_CMDS / (sizeof(long) * 8))
@@ -143,6 +148,8 @@ struct disk_part_tbl {
struct hd_struct __rcu *part[];
};
+struct disk_events;
+
struct gendisk {
/* major, first_minor and minors are input parameters only,
* don't use directly. Use disk_devt() and disk_max_parts().
@@ -154,6 +161,10 @@ struct gendisk {
char disk_name[DISK_NAME_LEN]; /* name of major driver */
char *(*devnode)(struct gendisk *gd, mode_t *mode);
+
+ unsigned int events; /* supported events */
+ unsigned int async_events; /* async events, subset of all */
+
/* Array of pointers to partitions indexed by partno.
* Protected with matching bdev lock but stat and other
* non-critical accesses use RCU. Always access through
@@ -171,8 +182,8 @@ struct gendisk {
struct kobject *slave_dir;
struct timer_rand_state *random;
-
atomic_t sync_io; /* RAID */
+ struct disk_events *ev;
#ifdef CONFIG_BLK_DEV_INTEGRITY
struct blk_integrity *integrity;
#endif
@@ -405,6 +416,11 @@ static inline int get_disk_ro(struct gendisk *disk)
return disk->part0.policy;
}
+extern void disk_block_events(struct gendisk *disk);
+extern void disk_unblock_events(struct gendisk *disk);
+extern void disk_check_events(struct gendisk *disk);
+extern unsigned int disk_clear_events(struct gendisk *disk, unsigned int mask);
+
/* drivers/char/random.c */
extern void add_disk_randomness(struct gendisk *disk);
extern void rand_initialize_disk(struct gendisk *disk);
--
1.7.1
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