On Thu, Jul 10, 2025 at 06:03:43PM +0100, fdmanana@xxxxxxxxxx wrote: > From: Filipe Manana <fdmanana@xxxxxxxx> > > Test that overwriting a file with mmap when the filesystem has no more > space available for data allocation works. The motivation here is to check > that NOCOW mode of a COW filesystem (such as btrfs) works as expected. > > This currently fails with btrfs but it's fixed by a kernel patch that has > the subject: > > btrfs: fix -ENOSPC mmap write failure on NOCOW files/extents > > Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx> > --- > > V2: Use _try_scratch_mkfs_sized; > Use _get_file_block_size instead of _get_block_size; > Add a more detailed comment about why dd is used to fill the fs. Thanks Filipe, it's going to be merged into patches-in-queue branch, and will be push in next fstests release (this weekend hopefully) Reviewed-by: Zorro Lang <zlang@xxxxxxxxxx> > > tests/generic/211 | 63 +++++++++++++++++++++++++++++++++++++++++++ > tests/generic/211.out | 6 +++++ > 2 files changed, 69 insertions(+) > create mode 100755 tests/generic/211 > create mode 100644 tests/generic/211.out > > diff --git a/tests/generic/211 b/tests/generic/211 > new file mode 100755 > index 00000000..e87d1e01 > --- /dev/null > +++ b/tests/generic/211 > @@ -0,0 +1,63 @@ > +#! /bin/bash > +# SPDX-License-Identifier: GPL-2.0 > +# Copyright (c) 2025 SUSE Linux Products GmbH. All Rights Reserved. > +# > +# FS QA Test 211 > +# > +# Test that overwriting a file with mmap when the filesystem has no more space > +# available for data allocation works. The motivation here is to check that > +# NOCOW mode of a COW filesystem (such as btrfs) works as expected. > +# > +. ./common/preamble > +_begin_fstest auto quick rw mmap > + > +. ./common/filter > + > +_require_scratch > + > +[ "$FSTYP" = "btrfs" ] && _fixed_by_kernel_commit xxxxxxxxxxxx \ > + "btrfs: fix -ENOSPC mmap write failure on NOCOW files/extents" > + > +# Use a 512M fs so that it's fast to fill it with data but not too small such > +# that on btrfs it results in a fs with mixed block groups - we want to have > +# dedicated block groups for data and metadata, so that after filling all the > +# data block groups we can do a NOCOW write with mmap (if we have enough free > +# metadata space available). > +fs_size=$(_small_fs_size_mb 512) > +_try_scratch_mkfs_sized $((fs_size * 1024 * 1024)) >>$seqres.full 2>&1 || \ > + _fail "mkfs failed" > +_scratch_mount > + > +touch $SCRATCH_MNT/foobar > + > +# Set the file to NOCOW mode on btrfs, which must be done while the file is > +# empty, otherwise it fails. > +if [ $FSTYP == "btrfs" ]; then > + _require_chattr C > + $CHATTR_PROG +C $SCRATCH_MNT/foobar > +fi > + > +# Add initial data to the file we will later overwrite with mmap. > +$XFS_IO_PROG -c "pwrite -S 0xab 0 1M" $SCRATCH_MNT/foobar | _filter_xfs_io > + > +# Now fill all the remaining space with data. We use dd because we want to fill > +# only data space in btrfs - creating files with __populate_fill_fs() would also > +# fill metadata space. We want to exhaust data space on btrfs but still have > +# metadata space available, as metadata is always COWed on btrfs, so that the > +# mmap writes below succeed (metadata space available but no more data space > +# available). > +blksz=$(_get_file_block_size $SCRATCH_MNT) > +dd if=/dev/zero of=$SCRATCH_MNT/filler bs=$blksz >>$seqres.full 2>&1 > + > +# Overwrite the file with a mmap write. Should succeed. > +$XFS_IO_PROG -c "mmap -w 0 1M" \ > + -c "mwrite -S 0xcd 0 1M" \ > + -c "munmap" \ > + $SCRATCH_MNT/foobar > + > +# Cycle mount and dump the file's content. We expect to see the new data. > +_scratch_cycle_mount > +_hexdump $SCRATCH_MNT/foobar > + > +# success, all done > +_exit 0 > diff --git a/tests/generic/211.out b/tests/generic/211.out > new file mode 100644 > index 00000000..71cdf0f8 > --- /dev/null > +++ b/tests/generic/211.out > @@ -0,0 +1,6 @@ > +QA output created by 211 > +wrote 1048576/1048576 bytes at offset 0 > +XXX Bytes, X ops; XX:XX:XX.X (XXX YYY/sec and XXX ops/sec) > +000000 cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd cd >................< > +* > +100000 > -- > 2.47.2 > >
