* [PATCH] btrfs: Document some invariants of seed code
@ 2020-08-12 14:04 Nikolay Borisov
2020-08-24 16:53 ` David Sterba
2020-08-26 9:13 ` Anand Jain
0 siblings, 2 replies; 3+ messages in thread
From: Nikolay Borisov @ 2020-08-12 14:04 UTC (permalink / raw)
To: linux-btrfs; +Cc: Nikolay Borisov
Without good understanding of how seed devices works it's hard to grok
some of what the code in open_seed_devices or btrfs_prepare_sprout does.
Add comments hopefully reducing some of the cognitive load.
Signed-off-by: Nikolay Borisov <nborisov@suse.com>
---
fs/btrfs/volumes.c | 15 +++++++++++++++
1 file changed, 15 insertions(+)
diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 631cb03b3513..f7ee7837e6bc 100644
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -2361,10 +2361,20 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
if (!fs_devices->seeding)
return -EINVAL;
+ /*
+ * Private copy of the seed devices, anchored at
+ * fs_info->fs_devices->seed_list
+ */
seed_devices = alloc_fs_devices(NULL, NULL);
if (IS_ERR(seed_devices))
return PTR_ERR(seed_devices);
+ /*
+ * It's necessary to retain a copy of the original seed fs_devices in
+ * fs_uuids so that filesystems which have been seeded can be
+ * successfully reference the seed device from open_seed_devices. This
+ * also supports multiple fs seed.
+ */
old_devices = clone_fs_devices(fs_devices);
if (IS_ERR(old_devices)) {
kfree(seed_devices);
@@ -6713,6 +6723,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
lockdep_assert_held(&uuid_mutex);
ASSERT(fsid);
+ /* This will match only for multi-device seed fs */
list_for_each_entry(fs_devices, &fs_info->fs_devices->seed_list, seed_list)
if (!memcmp(fs_devices->fsid, fsid, BTRFS_FSID_SIZE))
return fs_devices;
@@ -6732,6 +6743,10 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
return fs_devices;
}
+ /*
+ * Upon first call for a seed fs fsid just create a private copy of the
+ * respective fs_devices and anchor it at fs_info->fs_devices->seed_list
+ */
fs_devices = clone_fs_devices(fs_devices);
if (IS_ERR(fs_devices))
return fs_devices;
--
2.17.1
^ permalink raw reply related [flat|nested] 3+ messages in thread
* Re: [PATCH] btrfs: Document some invariants of seed code
2020-08-12 14:04 [PATCH] btrfs: Document some invariants of seed code Nikolay Borisov
@ 2020-08-24 16:53 ` David Sterba
2020-08-26 9:13 ` Anand Jain
1 sibling, 0 replies; 3+ messages in thread
From: David Sterba @ 2020-08-24 16:53 UTC (permalink / raw)
To: Nikolay Borisov; +Cc: linux-btrfs
On Wed, Aug 12, 2020 at 05:04:36PM +0300, Nikolay Borisov wrote:
> Without good understanding of how seed devices works it's hard to grok
> some of what the code in open_seed_devices or btrfs_prepare_sprout does.
>
> Add comments hopefully reducing some of the cognitive load.
>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
I'll add this patch to the seed list api patchset.
^ permalink raw reply [flat|nested] 3+ messages in thread
* Re: [PATCH] btrfs: Document some invariants of seed code
2020-08-12 14:04 [PATCH] btrfs: Document some invariants of seed code Nikolay Borisov
2020-08-24 16:53 ` David Sterba
@ 2020-08-26 9:13 ` Anand Jain
1 sibling, 0 replies; 3+ messages in thread
From: Anand Jain @ 2020-08-26 9:13 UTC (permalink / raw)
To: Nikolay Borisov, linux-btrfs
On 12/8/20 10:04 pm, Nikolay Borisov wrote:
> Without good understanding of how seed devices works it's hard to grok
> some of what the code in open_seed_devices or btrfs_prepare_sprout does.
>
> Add comments hopefully reducing some of the cognitive load.
>
> Signed-off-by: Nikolay Borisov <nborisov@suse.com>
> ---
> fs/btrfs/volumes.c | 15 +++++++++++++++
> 1 file changed, 15 insertions(+)
>
> diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
> index 631cb03b3513..f7ee7837e6bc 100644
> --- a/fs/btrfs/volumes.c
> +++ b/fs/btrfs/volumes.c
> @@ -2361,10 +2361,20 @@ static int btrfs_prepare_sprout(struct btrfs_fs_info *fs_info)
> if (!fs_devices->seeding)
> return -EINVAL;
>
> + /*
> + * Private copy of the seed devices, anchored at
> + * fs_info->fs_devices->seed_list
> + */
> seed_devices = alloc_fs_devices(NULL, NULL);
> if (IS_ERR(seed_devices))
> return PTR_ERR(seed_devices);
>
> + /*
> + * It's necessary to retain a copy of the original seed fs_devices in
> + * fs_uuids so that filesystems which have been seeded can be
> + * successfully reference the seed device from open_seed_devices. This
> + * also supports multiple fs seed.
> + */
>
> old_devices = clone_fs_devices(fs_devices);
> if (IS_ERR(old_devices)) {
> kfree(seed_devices);
> @@ -6713,6 +6723,7 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
> lockdep_assert_held(&uuid_mutex);
> ASSERT(fsid);
>
> + /* This will match only for multi-device seed fs */
> list_for_each_entry(fs_devices, &fs_info->fs_devices->seed_list, seed_list)
> if (!memcmp(fs_devices->fsid, fsid, BTRFS_FSID_SIZE))
> return fs_devices;
> @@ -6732,6 +6743,10 @@ static struct btrfs_fs_devices *open_seed_devices(struct btrfs_fs_info *fs_info,
> return fs_devices;
> }
>
> + /*
> + * Upon first call for a seed fs fsid just create a private copy of the
> + * respective fs_devices and anchor it at fs_info->fs_devices->seed_list
> + */
> fs_devices = clone_fs_devices(fs_devices);
> if (IS_ERR(fs_devices))
> return fs_devices;
>
Looks good. Thanks
Reviewed-by: Anand Jain <anand.jain@oracle.com>
^ permalink raw reply [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-08-26 9:13 UTC | newest]
Thread overview: 3+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2020-08-12 14:04 [PATCH] btrfs: Document some invariants of seed code Nikolay Borisov
2020-08-24 16:53 ` David Sterba
2020-08-26 9:13 ` Anand Jain
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).