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>

3 files changed, 21 insertions, 1 deletions

diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 83031bcf8366..05667e6989f1 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 f48501563917..997d22efdef0 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 56e17ed24816..13893aa2ac9d 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);