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Subject[PATCH 07/11] block: Add block layer notifications [ver #7]
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Date
Add a block layer notification mechanism whereby notifications about
block-layer events such as I/O errors, can be reported to a monitoring
process asynchronously.

Firstly, an event queue needs to be created:

fd = open("/dev/event_queue", O_RDWR);
ioctl(fd, IOC_WATCH_QUEUE_SET_SIZE, page_size << n);

then a notification can be set up to report block notifications via that
queue:

struct watch_notification_filter filter = {
.nr_filters = 1,
.filters = {
[0] = {
.type = WATCH_TYPE_BLOCK_NOTIFY,
.subtype_filter[0] = UINT_MAX;
},
},
};
ioctl(fd, IOC_WATCH_QUEUE_SET_FILTER, &filter);
watch_devices(fd, 12);

After that, records will be placed into the queue when, for example, errors
occur on a block device. Records are of the following format:

struct block_notification {
struct watch_notification watch;
__u64 dev;
__u64 sector;
} *n;

Where:

n->watch.type will be WATCH_TYPE_BLOCK_NOTIFY

n->watch.subtype will be the type of notification, such as
NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM.

n->watch.info & WATCH_INFO_LENGTH will indicate the length of the
record.

n->watch.info & WATCH_INFO_ID will be the second argument to
watch_devices(), shifted.

n->dev will be the device numbers munged together.

n->sector will indicate the affected sector (if appropriate for the
event).

Note that it is permissible for event records to be of variable length -
or, at least, the length may be dependent on the subtype.

Signed-off-by: David Howells <dhowells@redhat.com>
---

Documentation/watch_queue.rst | 4 +++-
block/Kconfig | 9 +++++++++
block/blk-core.c | 29 +++++++++++++++++++++++++++++
include/linux/blkdev.h | 15 +++++++++++++++
include/uapi/linux/watch_queue.h | 30 +++++++++++++++++++++++++++++-
5 files changed, 85 insertions(+), 2 deletions(-)

diff --git a/Documentation/watch_queue.rst b/Documentation/watch_queue.rst
index 393905b904c8..5cc9c6924727 100644
--- a/Documentation/watch_queue.rst
+++ b/Documentation/watch_queue.rst
@@ -7,7 +7,9 @@ receive notifications from the kernel. This can be used in conjunction with::

* Key/keyring notifications

- * General device event notifications
+ * General device event notifications, including::
+
+ * Block layer event notifications


The notifications buffers can be enabled by:
diff --git a/block/Kconfig b/block/Kconfig
index 8b5f8e560eb4..cc93e4ca29a7 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -164,6 +164,15 @@ config BLK_SED_OPAL
Enabling this option enables users to setup/unlock/lock
Locking ranges for SED devices using the Opal protocol.

+config BLK_NOTIFICATIONS
+ bool "Block layer event notifications"
+ depends on DEVICE_NOTIFICATIONS
+ help
+ This option provides support for getting block layer event
+ notifications. This makes use of the /dev/watch_queue misc device to
+ handle the notification buffer and provides the device_notify() system
+ call to enable/disable watches.
+
menu "Partition Types"

source "block/partitions/Kconfig"
diff --git a/block/blk-core.c b/block/blk-core.c
index d0cc6e14d2f0..8ab1e07aa311 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -181,6 +181,22 @@ static const struct {
[BLK_STS_IOERR] = { -EIO, "I/O" },
};

+#ifdef CONFIG_BLK_NOTIFICATIONS
+static const
+enum block_notification_type blk_notifications[ARRAY_SIZE(blk_errors)] = {
+ [BLK_STS_TIMEOUT] = NOTIFY_BLOCK_ERROR_TIMEOUT,
+ [BLK_STS_NOSPC] = NOTIFY_BLOCK_ERROR_NO_SPACE,
+ [BLK_STS_TRANSPORT] = NOTIFY_BLOCK_ERROR_RECOVERABLE_TRANSPORT,
+ [BLK_STS_TARGET] = NOTIFY_BLOCK_ERROR_CRITICAL_TARGET,
+ [BLK_STS_NEXUS] = NOTIFY_BLOCK_ERROR_CRITICAL_NEXUS,
+ [BLK_STS_MEDIUM] = NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM,
+ [BLK_STS_PROTECTION] = NOTIFY_BLOCK_ERROR_PROTECTION,
+ [BLK_STS_RESOURCE] = NOTIFY_BLOCK_ERROR_KERNEL_RESOURCE,
+ [BLK_STS_DEV_RESOURCE] = NOTIFY_BLOCK_ERROR_DEVICE_RESOURCE,
+ [BLK_STS_IOERR] = NOTIFY_BLOCK_ERROR_IO,
+};
+#endif
+
blk_status_t errno_to_blk_status(int errno)
{
int i;
@@ -221,6 +237,19 @@ static void print_req_error(struct request *req, blk_status_t status,
req->cmd_flags & ~REQ_OP_MASK,
req->nr_phys_segments,
IOPRIO_PRIO_CLASS(req->ioprio));
+
+#ifdef CONFIG_BLK_NOTIFICATIONS
+ if (blk_notifications[idx]) {
+ struct block_notification n = {
+ .watch.type = WATCH_TYPE_BLOCK_NOTIFY,
+ .watch.subtype = blk_notifications[idx],
+ .watch.info = watch_sizeof(n),
+ .dev = req->rq_disk ? disk_devt(req->rq_disk) : 0,
+ .sector = blk_rq_pos(req),
+ };
+ post_block_notification(&n);
+ }
+#endif
}

static void req_bio_endio(struct request *rq, struct bio *bio,
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1ef375dafb1c..5d856f670a8f 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -27,6 +27,7 @@
#include <linux/percpu-refcount.h>
#include <linux/scatterlist.h>
#include <linux/blkzoned.h>
+#include <linux/watch_queue.h>

struct module;
struct scsi_ioctl_command;
@@ -1742,6 +1743,20 @@ static inline bool blk_req_can_dispatch_to_zone(struct request *rq)
}
#endif /* CONFIG_BLK_DEV_ZONED */

+#ifdef CONFIG_BLK_NOTIFICATIONS
+static inline void post_block_notification(struct block_notification *n)
+{
+ u64 id = 0; /* Might want to allow dev# here. */
+
+ post_device_notification(&n->watch, id);
+}
+#else
+static inline void post_block_notification(struct block_notification *n)
+{
+}
+#endif
+
+
#else /* CONFIG_BLOCK */

struct block_device;
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 654d4ba8b909..9a6c059af09d 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -11,7 +11,8 @@
enum watch_notification_type {
WATCH_TYPE_META = 0, /* Special record */
WATCH_TYPE_KEY_NOTIFY = 1, /* Key change event notification */
- WATCH_TYPE___NR = 2
+ WATCH_TYPE_BLOCK_NOTIFY = 2, /* Block layer event notification */
+ WATCH_TYPE___NR = 3
};

enum watch_meta_notification_subtype {
@@ -124,4 +125,31 @@ struct key_notification {
__u32 aux; /* Per-type auxiliary data */
};

+/*
+ * Type of block layer notification.
+ */
+enum block_notification_type {
+ NOTIFY_BLOCK_ERROR_TIMEOUT = 1, /* Timeout error */
+ NOTIFY_BLOCK_ERROR_NO_SPACE = 2, /* Critical space allocation error */
+ NOTIFY_BLOCK_ERROR_RECOVERABLE_TRANSPORT = 3, /* Recoverable transport error */
+ NOTIFY_BLOCK_ERROR_CRITICAL_TARGET = 4, /* Critical target error */
+ NOTIFY_BLOCK_ERROR_CRITICAL_NEXUS = 5, /* Critical nexus error */
+ NOTIFY_BLOCK_ERROR_CRITICAL_MEDIUM = 6, /* Critical medium error */
+ NOTIFY_BLOCK_ERROR_PROTECTION = 7, /* Protection error */
+ NOTIFY_BLOCK_ERROR_KERNEL_RESOURCE = 8, /* Kernel resource error */
+ NOTIFY_BLOCK_ERROR_DEVICE_RESOURCE = 9, /* Device resource error */
+ NOTIFY_BLOCK_ERROR_IO = 10, /* Other I/O error */
+};
+
+/*
+ * Block layer notification record.
+ * - watch.type = WATCH_TYPE_BLOCK_NOTIFY
+ * - watch.subtype = enum block_notification_type
+ */
+struct block_notification {
+ struct watch_notification watch; /* WATCH_TYPE_BLOCK_NOTIFY */
+ __u64 dev; /* Device number */
+ __u64 sector; /* Affected sector */
+};
+
#endif /* _UAPI_LINUX_WATCH_QUEUE_H */
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