roots: filter out NODATASUM files before attempting to scan them

Add a cheap check for `FS_NOCOW_FL` when we first encounter
each extent.  In the raw btrfs inode flags, the offending flag is
`BTRFS_INODE_NODATASUM`, because the restriction that prevents reflink
between datacow and "nodatacow" files is that a single inode is allowed
to have csums or not have csums, but must apply that choice to _all_
of its extents.

This extra check is cheaper than opening a file for each individual
reference to the extent, and then discovering that the file is
`FS_NOCOW_FL`, and then closing the file, over and over again.  It will
also avoid emitting a lot of noisy log messages.

Fixes: https://github.com/Zygo/bees/issues/313
Signed-off-by: Zygo Blaxell <bees@furryterror.org>

diff --git a/src/bees-roots.cc b/src/bees-roots.cc
index 8d85721d5127936e2401d927bf3a19fa8f70c4e8..9b8ce68946481f073f055bab1154cb2c6eeb1986 100644 (file)
--- a/src/bees-roots.cc
+++ b/src/bees-roots.cc
@@ -183,26 +183,41 @@ BeesScanModeSubvol::crawl_one_inode(const shared_ptr<BeesCrawl>& this_crawl)
        }
        const auto subvol = this_range.fid().root();
        const auto inode = this_range.fid().ino();
-       ostringstream oss;
-       oss << "crawl_" << subvol << "_" << inode;
-       const auto task_title = oss.str();
-       const auto bfc = make_shared<BeesFileCrawl>((BeesFileCrawl) {
-               .m_ctx = m_ctx,
-               .m_crawl = this_crawl,
-               .m_roots = m_roots,
-               .m_hold = this_crawl->hold_state(this_state),
-               .m_state = this_state,
-               .m_offset = this_range.begin(),
+       bool run_the_task = false;
+       catch_all([&]() {
+               BtrfsInodeFetcher inode_btf(m_ctx->root_fd());
+               const auto inode_item = inode_btf.stat(subvol, inode);
+               if (!!inode_item) {
+                       const auto flags = inode_item.inode_flags();
+                       if (0 != (flags & BTRFS_INODE_NODATASUM)) {
+                               BEESLOGDEBUG("unsupported inode flags for ref at root " << subvol << " ino " << inode << ": " << btrfs_inode_flags_ntoa(flags));
+                       } else {
+                               run_the_task = true;
+                       }
+               }
        });
-       BEESNOTE("Starting task " << this_range);
-       Task(task_title, [bfc]() {
-               BEESNOTE("crawl_one_inode " << bfc->m_hold->get());
-               if (bfc->scan_one_ref()) {
-                       // Append the current task to itself to make
-                       // sure we keep a worker processing this file
-                       Task::current_task().append(Task::current_task());
-               }
-       }).run();
+       if (run_the_task) {
+               ostringstream oss;
+               oss << "crawl_" << subvol << "_" << inode;
+               const auto task_title = oss.str();
+               const auto bfc = make_shared<BeesFileCrawl>((BeesFileCrawl) {
+                       .m_ctx = m_ctx,
+                       .m_crawl = this_crawl,
+                       .m_roots = m_roots,
+                       .m_hold = this_crawl->hold_state(this_state),
+                       .m_state = this_state,
+                       .m_offset = this_range.begin(),
+               });
+               BEESNOTE("Starting task " << this_range);
+               Task(task_title, [bfc]() {
+                       BEESNOTE("crawl_one_inode " << bfc->m_hold->get());
+                       if (bfc->scan_one_ref()) {
+                               // Append the current task to itself to make
+                               // sure we keep a worker processing this file
+                               Task::current_task().append(Task::current_task());
+                       }
+               }).run();
+       }
        auto next_state = this_state;
        // Skip to EOF.  Will repeat up to 16 times if there happens to be an extent at 16EB,
        // which would be a neat trick given that off64_t is signed.
@@ -780,10 +795,27 @@ BeesScanModeExtent::SizeTier::create_extent_map(const uint64_t bytenr, const Pro
        }
 
        BtrfsExtentDataFetcher bedf(m_ctx->root_fd());
+       BtrfsInodeFetcher inode_btf(m_ctx->root_fd());
 
        const auto refs_list = make_shared<list<ExtentRef>>();
+       bool found_nocow = false;
+       bool check_nocow = true;
        for (const auto &i : log_ino.m_iors) {
                catch_all([&](){
+                       if (check_nocow) {
+                               BEESTRACE("checking inode flags for extent " << to_hex(bytenr) << " ref at root " << i.m_root << " ino " << i.m_inum);
+                               BEESNOTE("checking inode flags for extent " << to_hex(bytenr) << " ref at root " << i.m_root << " ino " << i.m_inum);
+                               const auto inode_item = inode_btf.stat(i.m_root, i.m_inum);
+                               if (!!inode_item) {
+                                       const auto flags = inode_item.inode_flags();
+                                       check_nocow = false;
+                                       if (0 != (flags & BTRFS_INODE_NODATASUM)) {
+                                               BEESLOGDEBUG("unsupported inode flags for extent " << to_hex(bytenr) << " ref at root " << i.m_root << " ino " << i.m_inum << ": " << btrfs_inode_flags_ntoa(flags));
+                                               found_nocow = true;
+                                               return; // from the catch_all
+                                       }
+                               }
+                       }
                        BEESTRACE("mapping extent " << to_hex(bytenr) << " ref at root " << i.m_root << " ino " << i.m_inum << " offset " << to_hex(i.m_offset));
                        BEESNOTE("mapping extent " << to_hex(bytenr) << " ref at root " << i.m_root << " ino " << i.m_inum << " offset " << to_hex(i.m_offset));
 
@@ -808,6 +840,11 @@ BeesScanModeExtent::SizeTier::create_extent_map(const uint64_t bytenr, const Pro
                        refs_list->push_back(extref);
                        BEESCOUNT(extent_ref_ok);
                });
+               // Completely abandon the extent if it is nodatasum
+               if (found_nocow) {
+                       BEESCOUNT(extent_nodatasum);
+                       return;
+               }
        }
        BEESCOUNT(extent_mapped);