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>
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 @@
{
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 @@
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 @@
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 @@
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);
