From: Qu Wenruo <quwenruo@cn.fujitsu.com>
To: <dsterba@suse.cz>, <linux-btrfs@vger.kernel.org>,
Karel Zak <kzak@redhat.com>
Subject: Re: [PATCH RFC] btrfs: Add ctime/mtime update for btrfs device add/remove.
Date: Wed, 4 Jun 2014 13:51:39 +0800 [thread overview]
Message-ID: <538EB3EB.2080309@cn.fujitsu.com> (raw)
In-Reply-To: <20140529124308.GA29992@twin.jikos.cz>
-------- Original Message --------
Subject: Re: [PATCH RFC] btrfs: Add ctime/mtime update for btrfs device
add/remove.
From: David Sterba <dsterba@suse.cz>
To: Qu Wenruo <quwenruo@cn.fujitsu.com>
Date: 2014年05月29日 20:43
> On Wed, Apr 16, 2014 at 05:02:32PM +0800, Qu Wenruo wrote:
>> @@ -1704,10 +1720,14 @@ int btrfs_rm_device(struct btrfs_root *root, char *device_path)
>>
>> ret = 0;
>>
>> - /* Notify udev that device has changed */
>> - if (bdev)
>> + if (bdev) {
>> + /* Notify udev that device has changed */
>> btrfs_kobject_uevent(bdev, KOBJ_CHANGE);
>>
>> + /* Update ctime/mtime for device path for libblkid */
>> + update_dev_time(device_path);
> The change on the device comes after the uevent notification, is it
> possible that the event is delivered and processed before the device
> times are updated? I would say so.
If I understand the udev thing right, uevent notification is sent to
udevd and udevd process the notification.
For btrfs_rm_device(), it will send KOBJ_CHANGE uevent to udevd, and
udevd will *update* the ctime/mtime in /dev.
But the problems is, there is a time lag between uevent sending and
udevd updating the ctime/mtime,
which makes the ctime/mtime updating later than next 'btrfs dev scan'
commands.
Since the ctime/mtime is not changed, libblkid used by 'btrfs dev scan'
will still consider the removed disk as btrfs,
causing the bug I reported.
IMO the best method to deal the bug is to wait udevd processing the
uevent, but unfortunately, we can't even guarantee
that there is a udevd processing the uevent(like some embedded system
without udevd).
So I use update_dev_time() as a workaround, which provide a completely
synchronize method to update device file ctime/mtime.
And even the uevent is processed before the update_dev_time(), it makes
no harm except a new ctime/mtime.
Thanks,
Qu
>
>> + }
>> +
>> error_brelse:
>> brelse(bh);
>> if (bdev)
next prev parent reply other threads:[~2014-06-04 5:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-04-16 9:02 [PATCH RFC] btrfs: Add ctime/mtime update for btrfs device add/remove Qu Wenruo
2014-05-29 12:43 ` David Sterba
2014-05-30 1:27 ` Qu Wenruo
2014-06-04 5:51 ` Qu Wenruo [this message]
2014-05-30 7:51 ` Anand Jain
2014-05-30 7:53 ` Anand Jain
2014-05-30 8:43 ` Qu Wenruo
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