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copy: don't avoid copy-offload upon SEEK_HOLE indicating non-sparse

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* src/copy-file-data.c (infer_scantype): Fall back to a plain copy
if SEEK_HOLE indicates non-sparse, as zero copy avoids copy offload.
This was seen with transparently compressed files on OpenZFS.
* tests/cp/sparse-perf.sh: Add a test case even though it might
only trigger on compressed file systems that don't support reflink.
* NEWS: Mention the bug fix.
Addresses https://github.com/coreutils/coreutils/issues/122
This commit is contained in:
Pádraig Brady
2025-10-30 13:02:48 +00:00
parent 231cc20195
commit 64b8fdb5b4
3 changed files with 27 additions and 2 deletions
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8
NEWS
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@@ -18,6 +18,10 @@ GNU coreutils NEWS -*- outline -*-
Also non standard SHA2 tags with a bad length resulted in undefined behavior.
[bug introduced in coreutils-9.8]
'cp' restores performance with transparently compressed files, which
regressed due to the avoidance of copy offload, seen with OpenZFS at least.
[bug introduced in coreutils-9.8]
'numfmt' no longer reads out-of-bounds memory with trailing blanks in input.
[bug introduced with numfmt in coreutils-8.21]
@@ -42,6 +46,10 @@ GNU coreutils NEWS -*- outline -*-
** Changes in behavior
'cp' with default options may again, like with versions before v9.8,
miss opportunities to create holes with file systems like squashfs,
that support SEEK_HOLE only trivially.
'sort --compress-program' will continue without compressing temporary files
if the specified program cannot be executed. Also malformed shell scripts
without a "shebang line" will no longer be executed.

11
src/copy-file-data.c
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@@ -481,12 +481,19 @@ infer_scantype (int fd, struct stat const *sb, off_t pos,
if (scan_inference->hole_start < sb->st_size)
return LSEEK_SCANTYPE;
/* Though the file likely has holes, SEEK_DATA and SEEK_HOLE
/* Though the file may have holes, SEEK_DATA and SEEK_HOLE
didn't find any. This can happen with file systems like
circa-2025 squashfs that support SEEK_HOLE only trivially.
Fall back on ZERO_SCANTYPE. */
This can also happen due to transparent file compression,
which can also indicate fewer than the usual number of blocks. */
if (lseek (fd, pos, SEEK_SET) < 0)
return ERROR_SCANTYPE;
/* we prefer to return PLAIN_SCANTYPE here so that copy offload
continues to be used. Falling through to ZERO_SCANTYPE would be
less performant in the compressed file case. */
return PLAIN_SCANTYPE;
}
}
else if (pos < scan_inference->ext_start || errno == ENXIO)

10
tests/cp/sparse-perf.sh
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@@ -35,6 +35,16 @@ cmp $other_partition_sparse k2 || fail=1
grep ': avoided' cp.out && { cat cp.out; fail=1; }
# Create a large-non-sparse-but-compressible file
# Ensure we don't avoid copy offload which we saw with
# transparent compression on OpenZFS at least
# (as that triggers our sparse heuristic).
mls='might-look-sparse'
yes | head -n1M > "$mls" || framework_failure_
cp --debug "$mls" "$mls.cp" >cp.out || fail=1
cmp "$mls" "$mls.cp" || fail=1
grep ': avoided' cp.out && { cat cp.out; fail=1; }
# Create a large-but-sparse file on the current partition.
# We disable relinking below, thus verifying SEEK_HOLE support