From: Nikolay Borisov <nborisov@suse.com>
To: linux-btrfs@vger.kernel.org
Cc: Nikolay Borisov <nborisov@suse.com>
Subject: [PATCH] btrfs: Document some invariants of seed code
Date: Wed, 12 Aug 2020 17:04:36 +0300 [thread overview]
Message-ID: <20200812140436.11749-1-nborisov@suse.com> (raw)
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
next reply other threads:[~2020-08-12 14:04 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-08-12 14:04 Nikolay Borisov [this message]
2020-08-24 16:53 ` [PATCH] btrfs: Document some invariants of seed code David Sterba
2020-08-26 9:13 ` Anand Jain
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