On Wed, Feb 22, 2023 at 7:40 PM Boris Burkov <boris@xxxxxx> wrote:
>
> btrfs recently had a bug where a direct io partial write resulted in a
> hole in the file. Add a new generic test which creates a 2MiB file,
> mmaps it, touches the first byte, then does an O_DIRECT write of the
> mmapped buffer into a new file. This should result in the mapped pages
> being a mix of in and out of page cache and thus a partial write, for
> filesystems using iomap and IOMAP_DIO_PARTIAL.
>
> Signed-off-by: Boris Burkov <boris@xxxxxx>
> ---
> .gitignore | 1 +
> src/Makefile | 2 +-
> src/dio-buf-fault.c | 83 +++++++++++++++++++++++++++++++++++++++++++
> tests/generic/708 | 48 +++++++++++++++++++++++++
> tests/generic/708.out | 2 ++
> 5 files changed, 135 insertions(+), 1 deletion(-)
> create mode 100644 src/dio-buf-fault.c
> create mode 100755 tests/generic/708
> create mode 100644 tests/generic/708.out
>
> diff --git a/.gitignore b/.gitignore
> index cfff8f85..644290f0 100644
> --- a/.gitignore
> +++ b/.gitignore
> @@ -72,6 +72,7 @@ tags
> /src/deduperace
> /src/detached_mounts_propagation
> /src/devzero
> +/src/dio-buf-fault
> /src/dio-interleaved
> /src/dio-invalidate-cache
> /src/dirhash_collide
> diff --git a/src/Makefile b/src/Makefile
> index a574f7bd..24cd4747 100644
> --- a/src/Makefile
> +++ b/src/Makefile
> @@ -19,7 +19,7 @@ TARGETS = dirstress fill fill2 getpagesize holes lstat64 \
> t_ofd_locks t_mmap_collision mmap-write-concurrent \
> t_get_file_time t_create_short_dirs t_create_long_dirs t_enospc \
> t_mmap_writev_overlap checkpoint_journal mmap-rw-fault allocstale \
> - t_mmap_cow_memory_failure fake-dump-rootino
> + t_mmap_cow_memory_failure fake-dump-rootino dio-buf-fault
>
> LINUX_TARGETS = xfsctl bstat t_mtab getdevicesize preallo_rw_pattern_reader \
> preallo_rw_pattern_writer ftrunc trunc fs_perms testx looptest \
> diff --git a/src/dio-buf-fault.c b/src/dio-buf-fault.c
> new file mode 100644
> index 00000000..36ff6710
> --- /dev/null
> +++ b/src/dio-buf-fault.c
> @@ -0,0 +1,83 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Copyright (c) 2023 Meta Platforms, Inc. All Rights Reserved.
> + */
> +
> +#ifndef _GNU_SOURCE
> +#define _GNU_SOURCE /* to get definition of O_DIRECT flag. */
> +#endif
> +
> +#include <sys/mman.h>
> +#include <sys/types.h>
> +#include <sys/stat.h>
> +#include <err.h>
> +#include <errno.h>
> +#include <fcntl.h>
> +#include <stdio.h>
> +#include <unistd.h>
> +
> +/*
> + * mmap a source file, then do a direct write of that mmapped region to a
> + * destination file.
> + */
> +
> +int prep_mmap_buffer(char *src_filename, int *fd, void **addr)
> +{
> + struct stat st;
> + int ret;
> +
> + *fd = open(src_filename, O_RDWR, 0666);
> + if (*fd == -1)
> + err(1, "failed to open %s", src_filename);
> +
> + ret = fstat(*fd, &st);
> + if (ret)
> + err(1, "failed to stat %d", *fd);
> +
> + *addr = mmap(NULL, st.st_size, PROT_READ, MAP_PRIVATE, *fd, 0);
> + if (*addr == MAP_FAILED)
> + err(1, "failed to mmap %d", *fd);
> +
> + return st.st_size;
> +}
> +
> +int do_dio(char *dst_filename, void *buf, size_t sz)
> +{
> + int fd;
> + ssize_t ret;
> +
> + fd = open(dst_filename, O_CREAT | O_TRUNC | O_WRONLY | O_DIRECT, 0666);
> + if (fd == -1)
> + err(1, "failed to open %s", dst_filename);
> + while (sz) {
> + ret = write(fd, buf, sz);
> + if (ret < 0) {
> + if (errno == -EINTR)
> + continue;
> + else
> + err(1, "failed to write %lu bytes to %d", sz, fd);
> + } else if (ret == 0) {
> + break;
> + }
> + buf += ret;
> + sz -= ret;
> + }
> + return sz;
> +}
> +
> +int main(int argc, char *argv[]) {
> + size_t sz;
> + int fd;
> + void *buf = NULL;
> + char c;
> +
> + if (argc != 3)
> + errx(1, "no in and out file name arguments given");
> + sz = prep_mmap_buffer(argv[1], &fd, &buf);
Minor thing: fd is not used by this function at all, can be moved to
prep_mmap_buffer().
> +
> + /* touch the first page of the mapping to bring it into cache */
> + c = ((char *)buf)[0];
> + printf("%u\n", c);
> +
> + do_dio(argv[2], buf, sz);
> +}
> diff --git a/tests/generic/708 b/tests/generic/708
> new file mode 100755
> index 00000000..ff2e162b
> --- /dev/null
> +++ b/tests/generic/708
> @@ -0,0 +1,48 @@
> +#! /bin/bash
> +# SPDX-License-Identifier: GPL-2.0
> +# Copyright (c) 2023 Meta Platforms, Inc. All Rights Reserved.
> +#
> +# FS QA Test 708
> +#
> +# Test iomap direct_io partial writes.
> +#
> +# Create a reasonably large file, then run a program which mmaps it,
> +# touches the first page, then dio writes it to a second file. This
> +# can result in a page fault reading from the mmapped dio write buffer and
> +# thus the iompap direct_io partial write codepath.
> +#
> +. ./common/preamble
> +_begin_fstest quick auto
> +_fixed_by_kernel_commit XXXX 'btrfs: fix dio continue after short write due to buffer page fault'
It would be odd if the test fails on another fs and then fstests
suggests that commit as a potential fix.
So just do the following as we do in other generic tests:
[ $FSTYP == "btrfs" ] && \
_fixed_by_kernel_commit ....
> +
> +# Override the default cleanup function.
> +_cleanup()
> +{
> + cd /
> + rm -r -f $tmp.*
> + rm -f $TEST_DIR/dio-buf-fault.*
> +}
> +
> +# Import common functions.
> +. ./common/filter
> +
> +# real QA test starts here
> +
> +# Modify as appropriate.
> +_supported_fs generic
> +_require_test
> +_require_odirect
> +_require_test_program dio-buf-fault
> +src=$TEST_DIR/dio-buf-fault.src
> +dst=$TEST_DIR/dio-buf-fault.dst
> +
> +echo "Silence is golden"
> +
> +$XFS_IO_PROG -fc "pwrite -q 0 $((2 * 1024 * 1024))" $src
This is fine for the purpose of detecting that we don't leave a hole
in the file as long as xfs_io decides to write bytes with a value
different than 0x00.
It happens to be that the default is 0xcd - it's not obvious and maybe
one day it changes to 0x00 - making it explicit by passing -S 0xcd,
or whatever value, makes it more clear IMO.
> +sync
Is the sync needed? Why? There should be a comment if it's needed.
Otherwise it looks fine to me. Thanks.
> +$here/src/dio-buf-fault $src $dst >> $seqres.full || _fail "failed doing the dio copy"
> +diff $src $dst
> +
> +# success, all done
> +status=$?
> +exit
> diff --git a/tests/generic/708.out b/tests/generic/708.out
> new file mode 100644
> index 00000000..33c478ad
> --- /dev/null
> +++ b/tests/generic/708.out
> @@ -0,0 +1,2 @@
> +QA output created by 708
> +Silence is golden
> --
> 2.39.1
>
