[PATCH 6/7] block: Add block layer notifications

David Howells
2019-05-28T16:02:48Z

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);
block_notify(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
block_notify(), 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>
---

arch/x86/entry/syscalls/syscall_32.tbl | 1
arch/x86/entry/syscalls/syscall_64.tbl | 1
block/Kconfig | 9 +++
block/Makefile | 1
block/blk-core.c | 28 +++++++++++
block/blk-notify.c | 83 ++++++++++++++++++++++++++++++++
include/linux/blkdev.h | 10 ++++
include/linux/syscalls.h | 1
include/uapi/linux/watch_queue.h | 28 +++++++++++
9 files changed, 162 insertions(+)
create mode 100644 block/blk-notify.c

diff --git a/arch/x86/entry/syscalls/syscall_32.tbl b/arch/x86/entry/syscalls/syscall_32.tbl
index 429416ce60e1..22793f77c5f1 100644
--- a/arch/x86/entry/syscalls/syscall_32.tbl
+++ b/arch/x86/entry/syscalls/syscall_32.tbl
@@ -441,3 +441,4 @@
434 i386 fsinfo sys_fsinfo __ia32_sys_fsinfo
435 i386 mount_notify sys_mount_notify __ia32_sys_mount_notify
436 i386 sb_notify sys_sb_notify __ia32_sys_sb_notify
+437 i386 block_notify sys_block_notify __ia32_sys_block_notify
diff --git a/arch/x86/entry/syscalls/syscall_64.tbl b/arch/x86/entry/syscalls/syscall_64.tbl
index 4ae146e472db..3f0b82272a9f 100644
--- a/arch/x86/entry/syscalls/syscall_64.tbl
+++ b/arch/x86/entry/syscalls/syscall_64.tbl
@@ -358,6 +358,7 @@
434 common fsinfo __x64_sys_fsinfo
435 common mount_notify __x64_sys_mount_notify
436 common sb_notify __x64_sys_sb_notify
+437 common block_notify __x64_sys_block_notify

#
# x32-specific system call numbers start at 512 to avoid cache impact
diff --git a/block/Kconfig b/block/Kconfig
index 1b220101a9cb..3b0a0ddb83ef 100644
--- a/block/Kconfig
+++ b/block/Kconfig
@@ -163,6 +163,15 @@ 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"
+ select WATCH_QUEUE
+ 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 block_notify() system
+ call to enable/disable watches.
+
menu "Partition Types"

source "block/partitions/Kconfig"
diff --git a/block/Makefile b/block/Makefile
index eee1b4ceecf9..2dca6273f8f3 100644
--- a/block/Makefile
+++ b/block/Makefile
@@ -35,3 +35,4 @@ obj-$(CONFIG_BLK_DEBUG_FS) += blk-mq-debugfs.o
obj-$(CONFIG_BLK_DEBUG_FS_ZONED)+= blk-mq-debugfs-zoned.o
obj-$(CONFIG_BLK_SED_OPAL) += sed-opal.o
obj-$(CONFIG_BLK_PM) += blk-pm.o
+obj-$(CONFIG_BLK_NOTIFICATIONS) += blk-notify.o
diff --git a/block/blk-core.c b/block/blk-core.c
index 419d600e6637..8325e33f0bcc 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -144,6 +144,21 @@ static const struct {
[BLK_STS_IOERR] = { -EIO, "I/O" },
};

+#ifdef CONFIG_BLK_NOTIFICATIONS
+static const enum block_notification_type blk_notifications[] = {
+ [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;
@@ -179,6 +194,19 @@ static void print_req_error(struct request *req, blk_status_t status)
req->rq_disk ? req->rq_disk->disk_name : "?",
(unsigned long long)blk_rq_pos(req),
req->cmd_flags);
+
+#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 = 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/block/blk-notify.c b/block/blk-notify.c
new file mode 100644
index 000000000000..b310aaf37e7c
--- /dev/null
+++ b/block/blk-notify.c
@@ -0,0 +1,83 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Block layer event notifications.
+ *
+ * Copyright (C) 2019 Red Hat, Inc. All Rights Reserved.
+ * Written by David Howells (dhowells@redhat.com)
+ */
+
+#include <linux/blkdev.h>
+#include <linux/watch_queue.h>
+#include <linux/syscalls.h>
+#include <linux/init_task.h>
+
+/*
+ * Global queue for watching for block layer events.
+ */
+static struct watch_list blk_watchers = {
+ .watchers = HLIST_HEAD_INIT,
+ .lock = __SPIN_LOCK_UNLOCKED(&blk_watchers.lock),
+};
+
+static DEFINE_SPINLOCK(blk_watchers_lock);
+
+/*
+ * Post superblock notifications.
+ *
+ * Note that there's only a global queue to which all events are posted. Might
+ * want to provide per-dev queues also.
+ */
+void post_block_notification(struct block_notification *n)
+{
+ u64 id = 0; /* Might want to allow dev# here. */
+
+ post_watch_notification(&blk_watchers, &n->watch, &init_cred, id);
+}
+
+/**
+ * sys_block_notify - Watch for superblock events.
+ * @watch_fd: The watch queue to send notifications to.
+ * @watch_id: The watch ID to be placed in the notification (-1 to remove watch)
+ */
+SYSCALL_DEFINE2(block_notify, int, watch_fd, int, watch_id)
+{
+ struct watch_queue *wqueue;
+ struct watch_list *wlist = &blk_watchers;
+ struct watch *watch;
+ long ret = -ENOMEM;
+ u64 id = 0; /* Might want to allow dev# here. */
+
+ if (watch_id < -1 || watch_id > 0xff)
+ return -EINVAL;
+
+ wqueue = get_watch_queue(watch_fd);
+ if (IS_ERR(wqueue)) {
+ ret = PTR_ERR(wqueue);
+ goto err;
+ }
+
+ if (watch_id >= 0) {
+ watch = kzalloc(sizeof(*watch), GFP_KERNEL);
+ if (!watch)
+ goto err_wqueue;
+
+ init_watch(watch, wqueue);
+ watch->id = id;
+ watch->info_id = (u32)watch_id << WATCH_INFO_ID__SHIFT;
+
+ spin_lock(&blk_watchers_lock);
+ ret = add_watch_to_object(watch, wlist);
+ spin_unlock(&blk_watchers_lock);
+ if (ret < 0)
+ kfree(watch);
+ } else {
+ spin_lock(&blk_watchers_lock);
+ ret = remove_watch_from_object(wlist, wqueue, id, false);
+ spin_unlock(&blk_watchers_lock);
+ }
+
+err_wqueue:
+ put_watch_queue(wqueue);
+err:
+ return ret;
+}
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 1aafeb923e7b..c28f8647a76d 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -43,6 +43,7 @@ struct pr_ops;
struct rq_qos;
struct blk_queue_stats;
struct blk_stat_callback;
+struct block_notification;

#define BLKDEV_MIN_RQ 4
#define BLKDEV_MAX_RQ 128 /* Default maximum */
@@ -1744,6 +1745,15 @@ static inline bool blk_req_can_dispatch_to_zone(struct request *rq)
}
#endif /* CONFIG_BLK_DEV_ZONED */

+#ifdef CONFIG_BLK_NOTIFICATIONS
+extern void post_block_notification(struct block_notification *n);
+#else
+static inline void post_block_notification(struct block_notification *n)
+{
+}
+#endif
+
+
#else /* CONFIG_BLOCK */

struct block_device;
diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 204a6dbcc34a..77a9d84f1fbd 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -1005,6 +1005,7 @@ asmlinkage long sys_mount_notify(int dfd, const char __user *path,
unsigned int at_flags, int watch_fd, int watch_id);
asmlinkage long sys_sb_notify(int dfd, const char __user *path,
unsigned int at_flags, int watch_fd, int watch_id);
+asmlinkage long sys_block_notify(int watch_fd, int watch_id);

/*
* Architecture-specific system calls
diff --git a/include/uapi/linux/watch_queue.h b/include/uapi/linux/watch_queue.h
index 3b5770889bba..fad276ffa2d0 100644
--- a/include/uapi/linux/watch_queue.h
+++ b/include/uapi/linux/watch_queue.h
@@ -44,6 +44,7 @@ struct watch_notification {
#define WATCH_INFO_FLAG_6 0x00400000
#define WATCH_INFO_FLAG_7 0x00800000
#define WATCH_INFO_ID 0xff000000 /* ID of watchpoint */
+#define WATCH_INFO_ID__SHIFT 24
};

#define WATCH_LENGTH_SHIFT 3
@@ -154,4 +155,31 @@ struct superblock_error_notification {
__u32 error_cookie;
};

+/*
+ * 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 notification record.
+ * - watch.type = WATCH_TYPE_BLOCK_NOTIFY
+ * - watch.subtype = enum block_notification_type
+ */
+struct block_notification {
+ struct watch_notification watch; /* WATCH_TYPE_SB_NOTIFY */
+ __u64 dev; /* Device number */
+ __u64 sector; /* Affected sector */
+};
+
#endif /* _UAPI_LINUX_WATCH_QUEUE_H */