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roots: simplify BeesRoots::transid_max_nocache

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BeesRoots::transid_max_nocache calls btrfs_get_root_transid() which
retrieves the transid of the root of the given Fd.  Since the FS_TREE
(subvol 5) is the root of the subvol hierarchy, it will always have
the highest transid on the filesystem, and we do not need to look at
any others.

Also fix a bug where we pass BTRFS_FS_TREE_OBJECTID instead of the
file descriptor root_fd() to btrfs_get_root_transid().  If BEESHOME
is somewhere on the same btrfs filesystem, and there are no leaked FDs
at bees startup, then BTRFS_FS_TREE_OBJECTID (5) usually has the same
integer value as a valid file descriptor of some object on the filesystem
that has a regularly increasing transid value.  If Fd 5 happens to be a
file in BEESHOME then bees itself drives the transid increments.  This,
combined with the search of all subvol roots, hides the bug (unless Fd
5 gets closed somehow).

Signed-off-by: Zygo Blaxell <bees@furryterror.org>
This commit is contained in:
Zygo Blaxell 2018-10-30 01:34:52 -04:00
parent 1a51bb53bf
commit bf6ae80eee
1 changed files with 1 additions and 31 deletions
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32
src/bees-roots.cc
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@ -202,38 +202,8 @@ BeesRoots::transid_max_nocache()
BEESNOTE("Calculating transid_max (" << rv << " as of root " << root << ")");
BEESTRACE("Calculating transid_max...");
rv = btrfs_get_root_transid(root);
rv = btrfs_get_root_transid(m_ctx->root_fd());
// XXX: Do we need any of this? Or is
// m_transid_re.update(btrfs_get_root_transid(BTRFS_FS_TREE_OBJECTID)) good enough?
BtrfsIoctlSearchKey sk;
sk.tree_id = BTRFS_ROOT_TREE_OBJECTID;
sk.min_type = sk.max_type = BTRFS_ROOT_BACKREF_KEY;
sk.min_objectid = root;
while (true) {
sk.nr_items = 1024;
sk.do_ioctl(m_ctx->root_fd());
if (sk.m_result.empty()) {
break;
}
for (auto i : sk.m_result) {
sk.next_min(i);
if (i.type == BTRFS_ROOT_BACKREF_KEY) {
if (i.transid > rv) {
BEESLOGDEBUG("transid_max root " << i.objectid << " parent " << i.offset << " transid " << i.transid);
BEESCOUNT(transid_max_miss);
}
root = i.objectid;
}
if (i.transid > rv) {
rv = i.transid;
}
}
}
m_transid_re.update(rv);
return rv;
}