roots: rework open_root_nocache to use btrfs-tree

This gets rid of one open-coded btrfs tree search.

Also reduce the log noise level for subvol open failures, and remove
some ancient references to `BEESLOG`.

Signed-off-by: Zygo Blaxell <bees@furryterror.org>

diff --git a/src/bees-roots.cc b/src/bees-roots.cc
index 618e3e16f1a53abbee7b833562aeff7723752483..008f7ae02168c6a2c16bbd682f18b9ec2cb1d631 100644 (file)
--- a/src/bees-roots.cc
+++ b/src/bees-roots.cc
@@ -1797,90 +1797,72 @@ BeesRoots::open_root_nocache(uint64_t rootid)
        }
 
        // Find backrefs for this rootid and follow up to root
-       BtrfsIoctlSearchKey sk;
-       sk.tree_id = BTRFS_ROOT_TREE_OBJECTID;
-       sk.min_objectid = sk.max_objectid = rootid;
-       sk.min_type = sk.max_type = BTRFS_ROOT_BACKREF_KEY;
+       BtrfsRootFetcher brf(m_ctx->root_fd());
+       const auto bti = brf.root_backref(rootid);
+       if (!bti) {
+               BEESLOGDEBUG("No path for rootid " << rootid);
+               BEESCOUNT(root_notfound);
+               return Fd();
+       }
 
-       BEESTRACE("sk " << sk);
-       while (sk.min_objectid <= rootid) {
-               sk.do_ioctl(m_ctx->root_fd());
+       // Get dirid (path from parent subvol's root to this subvol) and basename (in that dirid)
+       const auto dirid = bti.root_ref_dirid();
+       const auto name = bti.root_ref_name();
+       const auto parent_rootid = bti.offset();
+       BEESTRACE("parent_rootid " << parent_rootid << " dirid " << dirid << " name " << name);
 
-               if (sk.m_result.empty()) {
-                       break;
-               }
+       // Try to open the parent recursively
+       BEESCOUNT(root_parent_open_try);
+       Fd parent_fd = open_root(parent_rootid);
+       if (!parent_fd) {
+               BEESLOGTRACE("no parent_fd");
+               BEESCOUNT(root_parent_open_fail);
+               return Fd();
+       }
+       BEESCOUNT(root_parent_open_ok);
 
-               for (auto i : sk.m_result) {
-                       sk.next_min(i, BTRFS_ROOT_BACKREF_KEY);
-                       if (i.type == BTRFS_ROOT_BACKREF_KEY && i.objectid == rootid) {
-                               const auto dirid = btrfs_get_member(&btrfs_root_ref::dirid, i.m_data);
-                               const auto name_len = btrfs_get_member(&btrfs_root_ref::name_len, i.m_data);
-                               const auto name_start = sizeof(struct btrfs_root_ref);
-                               const auto name_end = name_len + name_start;
-                               THROW_CHECK2(runtime_error, i.m_data.size(), name_end, i.m_data.size() >= name_end);
-                               const string name(i.m_data.data() + name_start, i.m_data.data() + name_end);
-
-                               const auto parent_rootid = i.offset;
-                               // BEESLOG("parent_rootid " << parent_rootid << " dirid " << dirid << " name " << name);
-                               BEESTRACE("parent_rootid " << parent_rootid << " dirid " << dirid << " name " << name);
-                               BEESCOUNT(root_parent_open_try);
-                               Fd parent_fd = open_root(parent_rootid);
-                               if (!parent_fd) {
-                                       BEESLOGTRACE("no parent_fd");
-                                       BEESCOUNT(root_parent_open_fail);
-                                       continue;
-                               }
-                               BEESCOUNT(root_parent_open_ok);
-
-                               if (dirid != BTRFS_FIRST_FREE_OBJECTID) {
-                                       BEESTRACE("dirid " << dirid << " root " << rootid << " INO_PATH");
-                                       BtrfsIoctlInoPathArgs ino(dirid);
-                                       if (!ino.do_ioctl_nothrow(parent_fd)) {
-                                               BEESLOGINFO("dirid " << dirid << " inode path lookup failed in parent_fd " << name_fd(parent_fd) << ": " << strerror(errno));
-                                               BEESCOUNT(root_parent_path_fail);
-                                               continue;
-                                       }
-                                       if (ino.m_paths.empty()) {
-                                               BEESLOGINFO("dirid " << dirid << " inode has no paths in parent_fd " << name_fd(parent_fd));
-                                               BEESCOUNT(root_parent_path_empty);
-                                               continue;
-                                       }
-                                       // Theoretically there is only one, so don't bother looping.
-                                       BEESTRACE("dirid " << dirid << " path " << ino.m_paths.at(0));
-                                       parent_fd = bees_openat(parent_fd, ino.m_paths.at(0).c_str(), FLAGS_OPEN_DIR);
-                                       if (!parent_fd) {
-                                               BEESLOGTRACE("no parent_fd from dirid");
-                                               BEESCOUNT(root_parent_path_open_fail);
-                                               continue;
-                                       }
-                               }
-                               // BEESLOG("openat(" << name_fd(parent_fd) << ", " << name << ")");
-                               BEESTRACE("openat(" << name_fd(parent_fd) << ", " << name << ")");
-                               Fd rv = bees_openat(parent_fd, name.c_str(), FLAGS_OPEN_DIR);
-                               if (!rv) {
-                                       BEESLOGTRACE("open failed for name " << name << ": " << strerror(errno));
-                                       BEESCOUNT(root_open_fail);
-                                       continue;
-                               }
-                               BEESCOUNT(root_found);
-
-                               // Verify correct root ID
-                               // Throw exceptions here because these are very rare events
-                               // and unlike the file open case, we don't have alternatives to try
-                               auto new_root_id = btrfs_get_root_id(rv);
-                               THROW_CHECK2(runtime_error, new_root_id, rootid, new_root_id == rootid);
-                               Stat st(rv);
-                               THROW_CHECK1(runtime_error, st.st_ino, st.st_ino == BTRFS_FIRST_FREE_OBJECTID);
-                               // BEESLOGDEBUG("open_root_nocache " << rootid << ": " << name_fd(rv));
-
-                               BEESCOUNT(root_ok);
-                               return rv;
-                       }
+       if (dirid != BTRFS_FIRST_FREE_OBJECTID) {
+               BEESTRACE("dirid " << dirid << " root " << rootid << " INO_PATH");
+               BtrfsIoctlInoPathArgs ino(dirid);
+               if (!ino.do_ioctl_nothrow(parent_fd)) {
+                       BEESLOGDEBUG("dirid " << dirid << " inode path lookup failed in parent_fd " << name_fd(parent_fd) << ": " << strerror(errno));
+                       BEESCOUNT(root_parent_path_fail);
+                       return Fd();
+               }
+               if (ino.m_paths.empty()) {
+                       BEESLOGDEBUG("dirid " << dirid << " inode has no paths in parent_fd " << name_fd(parent_fd));
+                       BEESCOUNT(root_parent_path_empty);
+                       return Fd();
+               }
+               // Theoretically there is only one, so don't bother looping.
+               BEESTRACE("dirid " << dirid << " path " << ino.m_paths.at(0));
+               parent_fd = bees_openat(parent_fd, ino.m_paths.at(0).c_str(), FLAGS_OPEN_DIR);
+               if (!parent_fd) {
+                       BEESLOGTRACE("no parent_fd from dirid");
+                       BEESCOUNT(root_parent_path_open_fail);
+                       return Fd();
                }
        }
-       BEESLOGDEBUG("No path for rootid " << rootid);
-       BEESCOUNT(root_notfound);
-       return Fd();
+       BEESTRACE("openat(" << name_fd(parent_fd) << ", " << name << ")");
+       Fd rv = bees_openat(parent_fd, name.c_str(), FLAGS_OPEN_DIR);
+       if (!rv) {
+               BEESLOGTRACE("open failed for name " << name << ": " << strerror(errno));
+               BEESCOUNT(root_open_fail);
+               return rv;
+       }
+       BEESCOUNT(root_found);
+
+       // Verify correct root ID
+       // Throw exceptions here because these are very rare events
+       // and unlike the file open case, we don't have alternatives to try
+       const auto new_root_id = btrfs_get_root_id(rv);
+       THROW_CHECK2(runtime_error, new_root_id, rootid, new_root_id == rootid);
+       Stat st(rv);
+       THROW_CHECK1(runtime_error, st.st_ino, st.st_ino == BTRFS_FIRST_FREE_OBJECTID);
+       // BEESLOGDEBUG("open_root_nocache " << rootid << ": " << name_fd(rv));
+
+       BEESCOUNT(root_ok);
+       return rv;
 }
 
 Fd