Re: [PATCH 2/2] btrfs: add ioctl for directly writing compressed data

Nikolay Borisov
2019-09-05T10:34:01Z

On 4.09.19 г. 22:13 ч., Omar Sandoval wrote:
> From: Omar Sandoval <osandov@fb.com>
>
> This adds an API for writing compressed data directly to the filesystem.
> The use case that I have in mind is send/receive: currently, when
> sending data from one compressed filesystem to another, the sending side
> decompresses the data and the receiving side recompresses it before
> writing it out. This is wasteful and can be avoided if we can just send
> and write compressed extents. The send part will be implemented in a
> separate series, as this ioctl can stand alone.
>
> The interface is essentially pwrite(2) with some extra information:
>
> - The input buffer contains the compressed data.
> - Both the compressed and decompressed sizes of the data are given.
> - The compression type (zlib, lzo, or zstd) is given.
>
> The interface is general enough that it can be extended to encrypted or
> otherwise encoded extents in the future. A more detailed description,
> including restrictions and edge cases, is included in
> include/uapi/linux/btrfs.h.
>
> The implementation is similar to direct I/O: we have to flush any
> ordered extents, invalidate the page cache, and do the io
> tree/delalloc/extent map/ordered extent dance. From there, we can reuse
> the compression code with a minor modification to distinguish the new
> ioctl from writeback.
>
> Signed-off-by: Omar Sandoval <osandov@fb.com>

Should we choose to continue with this interface (based on Dave's
feedback) I'd rather see the following things changed:

> ---
> fs/btrfs/compression.c | 6 +-
> fs/btrfs/compression.h | 14 +--
> fs/btrfs/ctree.h | 6 ++
> fs/btrfs/file.c | 13 ++-
> fs/btrfs/inode.c | 192 ++++++++++++++++++++++++++++++++++++-
> fs/btrfs/ioctl.c | 95 ++++++++++++++++++
> include/uapi/linux/btrfs.h | 69 +++++++++++++
> 7 files changed, 380 insertions(+), 15 deletions(-)
>
> diff --git a/fs/btrfs/compression.c b/fs/btrfs/compression.c
> index b05b361e2062..6632dd8d2e4d 100644
> --- a/fs/btrfs/compression.c
> +++ b/fs/btrfs/compression.c
> @@ -276,7 +276,8 @@ static void end_compressed_bio_write(struct bio *bio)
> bio->bi_status == BLK_STS_OK);
> cb->compressed_pages[0]->mapping = NULL;
>
> - end_compressed_writeback(inode, cb);
> + if (cb->writeback)
> + end_compressed_writeback(inode, cb);
> /* note, our inode could be gone now */
>
> /*
> @@ -311,7 +312,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
> unsigned long compressed_len,
> struct page **compressed_pages,
> unsigned long nr_pages,
> - unsigned int write_flags)
> + unsigned int write_flags, bool writeback)
> {
> struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> struct bio *bio = NULL;
> @@ -336,6 +337,7 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
> cb->mirror_num = 0;
> cb->compressed_pages = compressed_pages;
> cb->compressed_len = compressed_len;
> + cb->writeback = writeback;
> cb->orig_bio = NULL;
> cb->nr_pages = nr_pages;
>
> diff --git a/fs/btrfs/compression.h b/fs/btrfs/compression.h
> index 4cb8be9ff88b..5b48eb730362 100644
> --- a/fs/btrfs/compression.h
> +++ b/fs/btrfs/compression.h
> @@ -6,6 +6,7 @@
> #ifndef BTRFS_COMPRESSION_H
> #define BTRFS_COMPRESSION_H
>
> +#include <linux/btrfs.h>
> #include <linux/sizes.h>
>
> /*
> @@ -47,6 +48,9 @@ struct compressed_bio {
> /* the compression algorithm for this bio */
> int compress_type;
>
> + /* Whether this is a write for writeback. */
> + bool writeback;
> +
> /* number of compressed pages in the array */
> unsigned long nr_pages;
>
> @@ -93,20 +97,12 @@ blk_status_t btrfs_submit_compressed_write(struct inode *inode, u64 start,
> unsigned long compressed_len,
> struct page **compressed_pages,
> unsigned long nr_pages,
> - unsigned int write_flags);
> + unsigned int write_flags, bool writeback);
> blk_status_t btrfs_submit_compressed_read(struct inode *inode, struct bio *bio,
> int mirror_num, unsigned long bio_flags);
>
> unsigned int btrfs_compress_str2level(unsigned int type, const char *str);
>
> -enum btrfs_compression_type {
> - BTRFS_COMPRESS_NONE = 0,
> - BTRFS_COMPRESS_ZLIB = 1,
> - BTRFS_COMPRESS_LZO = 2,
> - BTRFS_COMPRESS_ZSTD = 3,
> - BTRFS_COMPRESS_TYPES = 3,
> -};
> -
> struct workspace_manager {
> const struct btrfs_compress_op *ops;
> struct list_head idle_ws;
> diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> index 19d669d12ca1..9fae9b3f1f62 100644
> --- a/fs/btrfs/ctree.h
> +++ b/fs/btrfs/ctree.h
> @@ -2905,6 +2905,10 @@ int btrfs_run_delalloc_range(struct inode *inode, struct page *locked_page,
> int btrfs_writepage_cow_fixup(struct page *page, u64 start, u64 end);
> void btrfs_writepage_endio_finish_ordered(struct page *page, u64 start,
> u64 end, int uptodate);
> +
> +ssize_t btrfs_raw_write(struct kiocb *iocb, struct iov_iter *from,
> + struct btrfs_ioctl_raw_pwrite_args *raw);
> +
> extern const struct dentry_operations btrfs_dentry_operations;
>
> /* ioctl.c */
> @@ -2928,6 +2932,8 @@ int btrfs_add_inode_defrag(struct btrfs_trans_handle *trans,
> struct btrfs_inode *inode);
> int btrfs_run_defrag_inodes(struct btrfs_fs_info *fs_info);
> void btrfs_cleanup_defrag_inodes(struct btrfs_fs_info *fs_info);
> +ssize_t btrfs_do_write_iter(struct kiocb *iocb, struct iov_iter *from,
> + struct btrfs_ioctl_raw_pwrite_args *args);
> int btrfs_sync_file(struct file *file, loff_t start, loff_t end, int datasync);
> void btrfs_drop_extent_cache(struct btrfs_inode *inode, u64 start, u64 end,
> int skip_pinned);
> diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> index 8fe4eb7e5045..ed23aa65b2d5 100644
> --- a/fs/btrfs/file.c
> +++ b/fs/btrfs/file.c
> @@ -1872,8 +1872,8 @@ static void update_time_for_write(struct inode *inode)
> inode_inc_iversion(inode);
> }
>
> -static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> - struct iov_iter *from)
> +ssize_t btrfs_do_write_iter(struct kiocb *iocb, struct iov_iter *from,
> + struct btrfs_ioctl_raw_pwrite_args *raw)
> {
> struct file *file = iocb->ki_filp;
> struct inode *inode = file_inode(file);
> @@ -1965,7 +1965,9 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> if (sync)
> atomic_inc(&BTRFS_I(inode)->sync_writers);
>
> - if (iocb->ki_flags & IOCB_DIRECT) {
> + if (raw) {
> + num_written = btrfs_raw_write(iocb, from, raw);
> + } else if (iocb->ki_flags & IOCB_DIRECT) {
> num_written = __btrfs_direct_write(iocb, from);
> } else {
> num_written = btrfs_buffered_write(iocb, from);
> @@ -1996,6 +1998,11 @@ static ssize_t btrfs_file_write_iter(struct kiocb *iocb,
> return num_written ? num_written : err;
> }
>
> +static ssize_t btrfs_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
> +{
> + return btrfs_do_write_iter(iocb, from, NULL);
> +}
> +
> int btrfs_release_file(struct inode *inode, struct file *filp)
> {
> struct btrfs_file_private *private = filp->private_data;
> diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> index a0546401bc0a..c8eaa1e5bf06 100644
> --- a/fs/btrfs/inode.c
> +++ b/fs/btrfs/inode.c
> @@ -865,7 +865,7 @@ static noinline void submit_compressed_extents(struct async_chunk *async_chunk)
> ins.objectid,
> ins.offset, async_extent->pages,
> async_extent->nr_pages,
> - async_chunk->write_flags)) {
> + async_chunk->write_flags, true)) {
> struct page *p = async_extent->pages[0];
> const u64 start = async_extent->start;
> const u64 end = start + async_extent->ram_size - 1;
> @@ -10590,6 +10590,196 @@ void btrfs_set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end)
> }
> }
>
> +/* Currently, this only supports raw writes of compressed data. */
> +ssize_t btrfs_raw_write(struct kiocb *iocb, struct iov_iter *from,
> + struct btrfs_ioctl_raw_pwrite_args *raw)
> +{
> + struct file *file = iocb->ki_filp;
> + struct inode *inode = file_inode(file);
> + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> + struct btrfs_root *root = BTRFS_I(inode)->root;
> + struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
> + struct extent_changeset *data_reserved = NULL;
> + struct extent_state *cached_state = NULL;
> + unsigned long nr_pages, i;
> + struct page **pages;
> + u64 disk_num_bytes, num_bytes;
> + u64 start, end;
> + struct btrfs_key ins;
> + struct extent_map *em;
> + ssize_t ret;
> +
> + if (iov_iter_count(from) != raw->num_bytes) {
> + /*
> + * The write got truncated by generic_write_checks(). We can't
> + * do a partial raw write.
> + */
> + return -EFBIG;
> + }
> +
> + /* This should be handled higher up. */
> + ASSERT(raw->num_bytes != 0);

This is already checked, indirectly via rw_verify_area, there's :

if (unlikely((ssize_t) count < 0))
return retval;

So you can remove this assert.

> +
> + /* The extent size must be sane. */
> + if (raw->num_bytes > BTRFS_MAX_UNCOMPRESSED ||
> + raw->disk_num_bytes > BTRFS_MAX_COMPRESSED ||
> + raw->disk_num_bytes == 0)
> + return -EINVAL;
> +
> + /*
> + * The compressed data on disk must be sector-aligned. For convenience,
> + * we extend the compressed data with zeroes if it isn't.
> + */
> + disk_num_bytes = ALIGN(raw->disk_num_bytes, fs_info->sectorsize);
> + /*
> + * The extent in the file must also be sector-aligned. However, we allow
> + * a write which ends at or extends i_size to have an unaligned length;
> + * we round up the extent size and set i_size to the given length.
> + */
> + start = iocb->ki_pos;
> + if ((start & (fs_info->sectorsize - 1)))

if (!IS_ALIGNED(start, fs_info->sectorsize))

> + return -EINVAL;
> + if (start + raw->num_bytes >= inode->i_size) {
> + num_bytes = ALIGN(raw->num_bytes, fs_info->sectorsize);
> + } else {
> + num_bytes = raw->num_bytes;
> + if ((num_bytes & (fs_info->sectorsize - 1)))

ditto

> + return -EINVAL;
> + }
> + end = start + num_bytes - 1;
> +
> + /*
> + * It's valid for compressed data to be larger than or the same size as
> + * the decompressed data. However, for buffered I/O, we never write out
> + * a compressed extent unless it's smaller than the decompressed data,
> + * so for now, let's not allow creating such extents with the ioctl,
> + * either.
> + */
> + if (disk_num_bytes >= num_bytes)
> + return -EINVAL;
> +
> + nr_pages = DIV_ROUND_UP(disk_num_bytes, PAGE_SIZE);
> + pages = kcalloc(nr_pages, sizeof(struct page *),
> + GFP_USER | __GFP_NOWARN);
> + if (!pages)
> + return -ENOMEM;
> + for (i = 0; i < nr_pages; i++) {
> + unsigned long offset = i << PAGE_SHIFT, n;
> + char *kaddr;
> +
> + pages[i] = alloc_page(GFP_USER | __GFP_NOWARN);
> + if (!pages[i]) {
> + ret = -ENOMEM;
> + goto out_pages;
> + }
> + kaddr = kmap(pages[i]);
> + if (offset < raw->disk_num_bytes) {
> + n = min_t(unsigned long, PAGE_SIZE,
> + raw->disk_num_bytes - offset);
> + if (copy_from_user(kaddr, raw->buf + offset, n)) {
> + kunmap(pages[i]);
> + ret = -EFAULT;
> + goto out_pages;
> + }
> + } else {
> + n = 0;
> + }
> + if (n < PAGE_SIZE)
> + memset(kaddr + n, 0, PAGE_SIZE - n);
> + kunmap(pages[i]);
> + }
> +
> + for (;;) {
> + struct btrfs_ordered_extent *ordered;
> +
> + lock_extent_bits(io_tree, start, end, &cached_state);
> + ordered = btrfs_lookup_ordered_range(BTRFS_I(inode), start,
> + end - start + 1);
> + if (!ordered &&
> + !filemap_range_has_page(inode->i_mapping, start, end))
> + break;
> + if (ordered)
> + btrfs_put_ordered_extent(ordered);
> + unlock_extent_cached(&BTRFS_I(inode)->io_tree, start, end,
> + &cached_state);
> + cond_resched();
> + ret = btrfs_wait_ordered_range(inode, start, end);
> + if (ret)
> + goto out_pages;
> + ret = invalidate_inode_pages2_range(inode->i_mapping,
> + start >> PAGE_SHIFT,
> + end >> PAGE_SHIFT);
> + if (ret)
> + goto out_pages;
> + }

Won't btrfs_lock_and_flush_ordered_range suffice here? Perhaps call that
function + invalidate_inode_pages2_range ?

> +
> + ret = btrfs_delalloc_reserve_space(inode, &data_reserved, start,
> + num_bytes);
> + if (ret)
> + goto out_unlock;
> +
> + ret = btrfs_reserve_extent(root, num_bytes, disk_num_bytes,
> + disk_num_bytes, 0, 0, &ins, 1, 1);
> + if (ret)
> + goto out_delalloc_release;
> +
> + em = create_io_em(inode, start, num_bytes, start, ins.objectid,
> + ins.offset, ins.offset, num_bytes, raw->compression,
> + BTRFS_ORDERED_COMPRESSED);
> + if (IS_ERR(em)) {
> + ret = PTR_ERR(em);
> + goto out_free_reserve;
> + }
> + free_extent_map(em);
> +
> + ret = btrfs_add_ordered_extent_compress(inode, start, ins.objectid,
> + num_bytes, ins.offset,
> + BTRFS_ORDERED_COMPRESSED,
> + raw->compression);
> + if (ret) {
> + btrfs_drop_extent_cache(BTRFS_I(inode), start, end, 0);
> + goto out_free_reserve;
> + }
> + btrfs_dec_block_group_reservations(fs_info, ins.objectid);
> +
> + if (start + raw->num_bytes > inode->i_size)
> + i_size_write(inode, start + raw->num_bytes);
> +
> + unlock_extent_cached(io_tree, start, end, &cached_state);
> +
> + btrfs_delalloc_release_extents(BTRFS_I(inode), num_bytes, false);
> +
> + if (btrfs_submit_compressed_write(inode, start, num_bytes, ins.objectid,
> + ins.offset, pages, nr_pages, 0,
> + false)) {
> + struct page *page = pages[0];
> +
> + page->mapping = inode->i_mapping;
> + btrfs_writepage_endio_finish_ordered(page, start, end, 0);
> + page->mapping = NULL;
> + ret = -EIO;
> + goto out_pages;
> + }
> + iocb->ki_pos += raw->num_bytes;
> + return raw->num_bytes;
> +
> +out_free_reserve:
> + btrfs_dec_block_group_reservations(fs_info, ins.objectid);
> + btrfs_free_reserved_extent(fs_info, ins.objectid, ins.offset, 1);
> +out_delalloc_release:
> + btrfs_delalloc_release_space(inode, data_reserved, start, num_bytes,
> + true);
> +out_unlock:
> + unlock_extent_cached(io_tree, start, end, &cached_state);
> +out_pages:
> + for (i = 0; i < nr_pages; i++) {
> + if (pages[i])
> + put_page(pages[i]);
> + }
> + kfree(pages);
> + return ret;
> +}
> +
> #ifdef CONFIG_SWAP
> /*
> * Add an entry indicating a block group or device which is pinned by a

<snip>