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roots: filter out NODATASUM files before attempting to scan them

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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>
This commit is contained in:
Zygo Blaxell
2025-07-09 01:33:31 -04:00
parent e9e6870de8
commit 27b5b4e113
1 changed files with 56 additions and 19 deletions
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75
src/bees-roots.cc
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@@ -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(),
});
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());
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;
}
}
}).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);