linux-kernel - Re: [PATCH v4 5/5] loop: raise media

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Date:   Mon, 12 Jul 2021 07:54:44 +0100
From:   Christoph Hellwig <hch@...radead.org>
To:     Matteo Croce <mcroce@...ux.microsoft.com>
Cc:     linux-block@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>, linux-kernel@...r.kernel.org,
        Lennart Poettering <lennart@...ttering.net>,
        Luca Boccassi <bluca@...ian.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Damien Le Moal <damien.lemoal@....com>,
        Tejun Heo <tj@...nel.org>,
        Javier Gonz??lez <javier@...igon.com>,
        Niklas Cassel <niklas.cassel@....com>,
        Johannes Thumshirn <johannes.thumshirn@....com>,
        Hannes Reinecke <hare@...e.de>,
        Matthew Wilcox <willy@...radead.org>,
        Christoph Hellwig <hch@...radead.org>,
        JeffleXu <jefflexu@...ux.alibaba.com>
Subject: Re: [PATCH v4 5/5] loop: raise media_change event

So when I said plug into the disk events I did not mean that you need
to use all the polling stuff - we can just do the parts required
which are the uevents and invalidation with a new little helper
like this (needs the actual prototype and kerneldoc of course):

diff --git a/block/disk-events.c b/block/disk-events.c
index a75931ff5da4..0023ab1559b6 100644
--- a/block/disk-events.c
+++ b/block/disk-events.c
@@ -163,15 +163,31 @@ void disk_flush_events(struct gendisk *disk, unsigned int mask)
 	spin_unlock_irq(&ev->lock);
 }
 
+/*
+ * Tell userland about new events.  Only the events listed in @disk->events are
+ * reported, and only if DISK_EVENT_FLAG_UEVENT is set.  Otherwise, events are
+ * processed internally but never get reported to userland.
+ */
+static void disk_event_uevent(struct gendisk *disk, unsigned int events)
+{
+	char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };
+	int nr_events = 0, i;
+
+	for (i = 0; i < ARRAY_SIZE(disk_uevents); i++)
+		if (events & disk->events & (1 << i))
+			envp[nr_events++] = disk_uevents[i];
+
+	if (nr_events)
+		kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
+}
+
 static void disk_check_events(struct disk_events *ev,
 			      unsigned int *clearing_ptr)
 {
 	struct gendisk *disk = ev->disk;
-	char *envp[ARRAY_SIZE(disk_uevents) + 1] = { };
 	unsigned int clearing = *clearing_ptr;
 	unsigned int events;
 	unsigned long intv;
-	int nr_events = 0, i;
 
 	/* check events */
 	events = disk->fops->check_events(disk, clearing);
@@ -190,19 +206,8 @@ static void disk_check_events(struct disk_events *ev,
 
 	spin_unlock_irq(&ev->lock);
 
-	/*
-	 * Tell userland about new events.  Only the events listed in
-	 * @disk->events are reported, and only if DISK_EVENT_FLAG_UEVENT
-	 * is set. Otherwise, events are processed internally but never
-	 * get reported to userland.
-	 */
-	for (i = 0; i < ARRAY_SIZE(disk_uevents); i++)
-		if ((events & disk->events & (1 << i)) &&
-		    (disk->event_flags & DISK_EVENT_FLAG_UEVENT))
-			envp[nr_events++] = disk_uevents[i];
-
-	if (nr_events)
-		kobject_uevent_env(&disk_to_dev(disk)->kobj, KOBJ_CHANGE, envp);
+	if (disk->event_flags & DISK_EVENT_FLAG_UEVENT)
+		disk_event_uevent(disk, events);
 }
 
 /**
@@ -281,6 +286,21 @@ bool bdev_check_media_change(struct block_device *bdev)
 }
 EXPORT_SYMBOL(bdev_check_media_change);
 
+bool disk_force_media_change(struct gendisk *disk, unsigned int events)
+{
+	disk_event_uevent(disk, events);
+
+	if (!(events & DISK_EVENT_MEDIA_CHANGE))
+		return false;
+
+	if (__invalidate_device(disk->part0, true))
+		pr_warn("VFS: busy inodes on changed media %s\n",
+			disk->disk_name);
+	set_bit(GD_NEED_PART_SCAN, &disk->state);
+	return true;
+}
+EXPORT_SYMBOL_GPL(disk_force_media_change);
+
 /*
  * Separate this part out so that a different pointer for clearing_ptr can be
  * passed in for disk_clear_events.