From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Sergei Shtepa <sergei.shtepa@veeam.com>
Cc: Damien Le Moal <Damien.LeMoal@wdc.com>,
Hannes Reinecke <hare@suse.de>,
"axboe@kernel.dk" <axboe@kernel.dk>,
"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
"hch@infradead.org" <hch@infradead.org>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"rjw@rjwysocki.net" <rjw@rjwysocki.net>,
"len.brown@intel.com" <len.brown@intel.com>,
"pavel@ucw.cz" <pavel@ucw.cz>,
"akpm@linux-foundation.org" <akpm@linux-foundation.org>,
Johannes Thumshirn <Johannes.Thumshirn@wdc.com>,
"ming.lei@redhat.com" <ming.lei@redhat.com>,
"jack@suse.cz" <jack@suse.cz>, "tj@kernel.org" <tj@kernel.org>,
"gustavo@embeddedor.com" <gustavo@embeddedor.com>,
"bvanassche@acm.org" <bvanassche@acm.org>,
"osandov@fb.com" <osandov@fb.com>,
"koct9i@gmail.com" <koct9i@gmail.com>,
"steve@sk2.org" <steve@sk2.org>,
"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"linux-pm@vger.kernel.org" <linux-pm@vger.kernel.org>,
"linux-mm@kvack.org" <linux-mm@kvack.org>
Subject: Re: [PATCH 0/2] block layer filter and block device snapshot module
Date: Thu, 22 Oct 2020 08:14:18 -0700 [thread overview]
Message-ID: <20201022151418.GR9832@magnolia> (raw)
In-Reply-To: <20201022135213.GB21466@veeam.com>
On Thu, Oct 22, 2020 at 04:52:13PM +0300, Sergei Shtepa wrote:
> The 10/22/2020 13:28, Damien Le Moal wrote:
> > On 2020/10/22 18:43, Sergei Shtepa wrote:
> > >
> > > Maybe, but the problem is that I can't imagine how to implement
> > > dm-intercept yet.
> > > How to use dm to implement interception without changing the stack
> > > of block devices. We'll have to make a hook somewhere, isn`t it?
> >
> > Once your dm-intercept target driver is inserted with "dmsetup" or any user land
> > tool you implement using libdevicemapper, the "hooks" will naturally be in place
> > since the dm infrastructure already does that: all submitted BIOs will be passed
> > to dm-intercept through the "map" operation defined in the target_type
> > descriptor. It is then that driver job to execute the BIOs as it sees fit.
> >
> > Look at simple device mappers like dm-linear or dm-flakey for hints of how
> > things work (driver/md/dm-linear.c). More complex dm drivers like dm-crypt,
> > dm-writecache or dm-thin can give you hints about more features of device mapper.
> > Functions such as __map_bio() in drivers/md/dm.c are the core of DM and show
> > what happens to BIOs depending on the the return value of the map operation.
> > dm_submit_bio() and __split_and_process_bio() is the entry points for BIO
> > processing in DM.
> >
>
> Is there something I don't understand? Please correct me.
>
> Let me remind that by the condition of the problem, we can't change
> the configuration of the block device stack.
>
> Let's imagine this configuration: /root mount point on ext filesystem
> on /dev/sda1.
> +---------------+
> | |
> | /root |
> | |
> +---------------+
> | |
> | EXT FS |
> | |
> +---------------+
> | |
> | block layer |
> | |
> | sda queue |
> | |
> +---------------+
> | |
> | scsi driver |
> | |
> +---------------+
>
> We need to add change block tracking (CBT) and snapshot functionality for
> incremental backup.
>
> With the DM we need to change the block device stack. Add device /dev/sda1
> to LVM Volume group, create logical volume, change /etc/fstab and reboot.
>
> The new scheme will look like this:
> +---------------+
> | |
> | /root |
> | |
> +---------------+
> | |
> | EXT FS |
> | |
> +---------------+
> | |
> | LV-root |
> | |
> +------------------+
> | |
> | dm-cbt & dm-snap |
> | |
> +------------------+
> | |
> | sda queue |
> | |
> +---------------+
> | |
> | scsi driver |
> | |
> +---------------+
>
> But I cannot change block device stack. And so I propose a scheme with
> interception.
> +---------------+
> | |
> | /root |
> | |
> +---------------+
> | |
> | EXT FS |
> | |
> +---------------+ +-----------------+
> | | | | |
> | | blk-filter |-> | cbt & snapshot |
> | | |<- | |
> | +------------+ +-----------------+
> | |
> | sda blk queue |
> | |
> +---------------+
> | |
> | scsi driver |
> | |
> +---------------+
>
> Perhaps I can make "cbt & snapshot" inside the DM, but without interception
> in any case, it will not work. Isn't that right?
Stupid question: Why don't you change the block layer to make it
possible to insert device mapper devices after the blockdev has been set
up?
--D
>
> --
> Sergei Shtepa
> Veeam Software developer.
next prev parent reply other threads:[~2020-10-22 15:15 UTC|newest]
Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-10-21 9:04 [PATCH 0/2] block layer filter and block device snapshot module Sergei Shtepa
2020-10-21 9:04 ` [PATCH 1/2] Block layer filter - second version Sergei Shtepa
2020-10-21 9:14 ` Johannes Thumshirn
2020-10-21 10:01 ` Sergei Shtepa
2020-10-21 9:21 ` Damien Le Moal
2020-10-21 10:27 ` Sergei Shtepa
2020-10-21 11:44 ` Matthew Wilcox
2020-10-21 12:55 ` Sergei Shtepa
2020-10-21 13:07 ` Matthew Wilcox
2020-10-21 14:35 ` Sergei Shtepa
2020-10-21 15:09 ` Randy Dunlap
2020-10-24 14:53 ` Greg KH
[not found] ` <1603271049-20681-3-git-send-email-sergei.shtepa@veeam.com>
2020-10-21 9:08 ` [PATCH 2/2] blk-snap - snapshots and change-tracking for block devices Pavel Machek
2020-10-21 9:37 ` Sergei Shtepa
[not found] ` <BL0PR04MB65142D9F391FE8777F096EF5E71C0@BL0PR04MB6514.namprd04.prod.outlook.com>
2020-10-21 11:15 ` Sergei Shtepa
2020-10-21 15:11 ` Randy Dunlap
2020-10-21 13:31 ` [PATCH 0/2] block layer filter and block device snapshot module Hannes Reinecke
2020-10-21 14:10 ` Sergei Shtepa
2020-10-22 5:58 ` Hannes Reinecke
2020-10-22 9:44 ` Sergei Shtepa
2020-10-22 10:28 ` Damien Le Moal
2020-10-22 13:52 ` Sergei Shtepa
2020-10-22 15:14 ` Darrick J. Wong [this message]
2020-10-22 17:54 ` Mike Snitzer
2020-10-23 9:13 ` hch
2020-10-23 10:31 ` Hannes Reinecke
2020-10-23 11:04 ` Sergei Shtepa
2020-10-23 11:12 ` [dm-devel] " hch
2020-10-22 18:35 ` Mike Snitzer
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