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List: linux-bcache
Subject: Re: [PATCH 3/3] bcache: support overlay bcache
From: mingzhe <mingzhe.zou () easystack ! cn>
Date: 2023-02-02 5:48:47
Message-ID: 994cd286-1929-60e2-8be9-71efd825ae84 () easystack ! cn
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在 2023/2/2 02:13, Eric Wheeler 写道:
> On Wed, 1 Feb 2023, mingzhe.zou@easystack.cn wrote:
> > From: Dongsheng Yang <dongsheng.yang@easystack.cn>
> >
> > If we want to build a bcache device with backing device of a bcache flash device,
> > we will fail with creating a duplicated sysfs filename.
> >
> > E.g:
> > (1) we create bcache0 with vdc, then there is "/sys/block/bcache0/bcache" as a \
> > link to "/sys/block/vdc/bcache" $ readlink /sys/block/bcache0/bcache
> > ../../../pci0000:00/0000:00:0b.0/virtio4/block/vdc/bcache
> >
> > (2) if we continue to create bcache1 with bcache0:
> > $ make-bcache -B /dev/bcache0
> >
> > We will fail to register bdev with "sysfs: cannot create duplicate
> > filename '/devices/virtual/block/bcache0/bcache'"
> >
> > How this commit solving this problem?
> > E.g:
> > we have vdf as cache disk, vdc as backing disk.
> >
> > $ make-bcache -C /dev/vdf -B /dev/vdc --wipe-bcache
> > $ echo 100G > /sys/block/vdf/bcache_cache/set/flash_vol_create
> > $ lsblk
> > NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
> > vdf 252:80 0 50G 0 disk
> > ├─bcache0 251:0 0 100G 0 disk
> > └─bcache1 251:128 0 100G 0 disk
> > vdc 252:32 0 100G 0 disk
> > └─bcache0 251:0 0 100G 0 disk
> >
> > (a) rename sysfs file to more meaningful name:
> > (a.2) bcahce_cache -> sysfs filename under cache disk \
> > (/sys/block/vdf/bcache_cache) (a.1) bcache_fdev -> flash bcache device \
> > (/sys/block/bcache1/bcache_fdev) (a.4) bcache_bdev -> sysfs filename for backing \
> > disk (/sys/block/vdc/bcache_bdev) (a.3) bcache_cdev -> link to \
> > /sys/block/vdc/bcache_bdev (/sys/block/bcache0/bcache_cdev)
>
> Good idea.
>
> > (b) create ->bcache lagacy link file for backward compatability
> > $ ll /sys/block/vdc/bcache
> > lrwxrwxrwx 1 root root 0 Oct 26 11:21 /sys/block/vdc/bcache -> bcache_bdev
> > $ ll /sys/block/bcache0/bcache
> > lrwxrwxrwx 1 root root 0 Oct 26 11:21 /sys/block/bcache0/bcache -> \
> > ../../../pci0000:00/0000:00:0b.0/virtio4/block/vdc/bcache_bdev $ ll \
> > /sys/block/bcache1/bcache lrwxrwxrwx 1 root root 0 Oct 26 11:19 \
> > /sys/block/bcache1/bcache -> bcache_fdev $ ll /sys/block/vdf/bcache
> > lrwxrwxrwx 1 root root 0 Oct 26 11:17 /sys/block/vdf/bcache -> bcache_cache
> >
> > These link are created with sysfs_create_link_nowarn(), that means, we dont
> > care about the failure when creating if these links are already created.
> > Because these lagacy sysfile are only for backwards compatability in no-overlay \
> > usecase of bcache, in the no-overlay use, bcache will never create duplicated \
> > link.
>
> awesome.
>
> > In overlay usecase after this commit, please dont use bcache link any more, \
> > instead use bcache_cdev, bcache_fdev, bcache_bdev or bcache_cache.
> >
> > Then we can create a cached_dev with bcache1 (flash dev) as backing dev.
> > $ make-bcache -B /dev/bcache1
> > $ lsblk
> > NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
> > vdf 252:80 0 50G 0 disk
> > ├─bcache0 251:0 0 100G 0 disk
> > └─bcache1 251:128 0 100G 0 disk
> > └─bcache2 251:256 0 100G 0 disk
> >
> > As a result there is a cached device bcache2 with backing device of a flash \
> > device bcache1.
> > ----------------------------
> > > bcache2 (cached_dev) |
> > > ------------------------ |
> > > > sdb (cache_dev) | |
> > > ------------------------ |
> > > ------------------------ |
> > > > bcache1 (flash_dev)| |
> > > ------------------------ |
> > ----------------------------
>
> Does this allow an arbitrary depth of bcache stacking?
>
> -Eric
>
More than 2 layers we did not test, but should be allowed.
mingzhe
> >
> > Signed-off-by: Dongsheng Yang <dongsheng.yang@easystack.cn>
> > Signed-off-by: mingzhe <mingzhe.zou@easystack.cn>
> > ---
> > drivers/md/bcache/super.c | 40 +++++++++++++++++++++++++++++++++++----
> > 1 file changed, 36 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> > index ba3909bb6bea..0ca8c05831c9 100644
> > --- a/drivers/md/bcache/super.c
> > +++ b/drivers/md/bcache/super.c
> > @@ -1087,12 +1087,19 @@ int bch_cached_dev_run(struct cached_dev *dc)
> >
> > if (sysfs_create_link(&d->kobj, &disk_to_dev(d->disk)->kobj, "dev") ||
> > sysfs_create_link(&disk_to_dev(d->disk)->kobj,
> > - &d->kobj, "bcache")) {
> > + &d->kobj, "bcache_cdev")) {
> > pr_err("Couldn't create bcache dev <-> disk sysfs symlinks\n");
> > ret = -ENOMEM;
> > goto out;
> > }
> >
> > + ret = sysfs_create_link_nowarn(&disk_to_dev(d->disk)->kobj,
> > + &d->kobj, "bcache");
> > + if (ret && ret != -EEXIST) {
> > + pr_err("Couldn't create lagacy disk sysfs ->bcache symlinks\n");
> > + goto out;
> > + }
> > +
> > dc->status_update_thread = kthread_run(cached_dev_status_update,
> > dc, "bcache_status_update");
> > if (IS_ERR(dc->status_update_thread)) {
> > @@ -1461,8 +1468,17 @@ static int register_bdev(struct cache_sb *sb, struct \
> > cache_sb_disk *sb_disk, goto err;
> >
> > err = "error creating kobject";
> > - if (kobject_add(&dc->disk.kobj, bdev_kobj(bdev), "bcache"))
> > + if (kobject_add(&dc->disk.kobj, bdev_kobj(bdev), "bcache_bdev"))
> > goto err;
> > +
> > + err = "error creating lagacy sysfs link";
> > + ret = sysfs_create_link_nowarn(&part_to_dev(bdev->bd_part)->kobj,
> > + &dc->disk.kobj, "bcache");
> > + if (ret && ret != -EEXIST) {
> > + pr_err("Couldn't create lagacy disk sysfs ->bcache");
> > + goto err;
> > + }
> > +
> > if (bch_cache_accounting_add_kobjs(&dc->accounting, &dc->disk.kobj))
> > goto err;
> >
> > @@ -1524,6 +1540,7 @@ static void flash_dev_flush(struct closure *cl)
> >
> > static int flash_dev_run(struct cache_set *c, struct uuid_entry *u)
> > {
> > + int ret;
> > int err = -ENOMEM;
> > struct bcache_device *d = kzalloc(sizeof(struct bcache_device),
> > GFP_KERNEL);
> > @@ -1546,10 +1563,17 @@ static int flash_dev_run(struct cache_set *c, struct \
> > uuid_entry *u) if (err)
> > goto err;
> >
> > - err = kobject_add(&d->kobj, &disk_to_dev(d->disk)->kobj, "bcache");
> > + err = kobject_add(&d->kobj, &disk_to_dev(d->disk)->kobj, "bcache_fdev");
> > if (err)
> > goto err;
> >
> > + ret = sysfs_create_link_nowarn(&disk_to_dev(d->disk)->kobj,
> > + &d->kobj, "bcache");
> > + if (ret && ret != -EEXIST) {
> > + pr_err("Couldn't create lagacy flash dev ->bcache");
> > + goto err;
> > + }
> > +
> > bcache_device_link(d, c, "volume");
> >
> > if (bch_has_feature_obso_large_bucket(&c->cache->sb)) {
> > @@ -2370,12 +2394,20 @@ static int register_cache(struct cache_sb *sb, struct \
> > cache_sb_disk *sb_disk, goto err;
> > }
> >
> > - if (kobject_add(&ca->kobj, bdev_kobj(bdev), "bcache")) {
> > + if (kobject_add(&ca->kobj, bdev_kobj(bdev), "bcache_cache")) {
> > err = "error calling kobject_add";
> > ret = -ENOMEM;
> > goto out;
> > }
> >
> > + ret = sysfs_create_link_nowarn(&part_to_dev(bdev->bd_part)->kobj,
> > + &ca->kobj, "bcache");
> > + if (ret && ret != -EEXIST) {
> > + pr_err("Couldn't create lagacy disk sysfs ->cache symlinks\n");
> > + goto out;
> > + } else
> > + ret = 0;
> > +
> > mutex_lock(&bch_register_lock);
> > err = register_cache_set(ca);
> > mutex_unlock(&bch_register_lock);
> > --
> > 2.17.1
> >
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