On Thu, Dec 03, 2020 at 09:32:37AM -0500, Josef Bacik wrote:
> On 11/18/20 2:18 PM, Omar Sandoval wrote:
> > From: Omar Sandoval <osandov@xxxxxx>
> >
> > There are 4 main cases:
> >
> > 1. Inline extents: we copy the data straight out of the extent buffer.
> > 2. Hole/preallocated extents: we fill in zeroes.
> > 3. Regular, uncompressed extents: we read the sectors we need directly
> > from disk.
> > 4. Regular, compressed extents: we read the entire compressed extent
> > from disk and indicate what subset of the decompressed extent is in
> > the file.
> >
> > This initial implementation simplifies a few things that can be improved
> > in the future:
> >
> > - We hold the inode lock during the operation.
> > - Cases 1, 3, and 4 allocate temporary memory to read into before
> > copying out to userspace.
> > - We don't do read repair, because it turns out that read repair is
> > currently broken for compressed data.
> >
> > Signed-off-by: Omar Sandoval <osandov@xxxxxx>
> > ---
> > fs/btrfs/ctree.h | 2 +
> > fs/btrfs/file.c | 5 +
> > fs/btrfs/inode.c | 496 +++++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 503 insertions(+)
> >
> > diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
> > index 6ab2ab002bf6..ce78424f1d98 100644
> > --- a/fs/btrfs/ctree.h
> > +++ b/fs/btrfs/ctree.h
> > @@ -3133,6 +3133,8 @@ int btrfs_run_delalloc_range(struct btrfs_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_encoded_read(struct kiocb *iocb, struct iov_iter *iter);
> > +
> > extern const struct dentry_operations btrfs_dentry_operations;
> > extern const struct iomap_ops btrfs_dio_iomap_ops;
> > extern const struct iomap_dio_ops btrfs_dio_ops;
> > diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
> > index 224295f8f1e1..193477565200 100644
> > --- a/fs/btrfs/file.c
> > +++ b/fs/btrfs/file.c
> > @@ -3629,6 +3629,11 @@ static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
> > {
> > ssize_t ret = 0;
> > + if (iocb->ki_flags & IOCB_ENCODED) {
> > + if (iocb->ki_flags & IOCB_NOWAIT)
> > + return -EOPNOTSUPP;
> > + return btrfs_encoded_read(iocb, to);
> > + }
> > if (iocb->ki_flags & IOCB_DIRECT) {
> > ret = btrfs_direct_read(iocb, to);
> > if (ret < 0 || !iov_iter_count(to) ||
> > diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
> > index 1ff903f5c5a4..b0e800897b3b 100644
> > --- a/fs/btrfs/inode.c
> > +++ b/fs/btrfs/inode.c
> > @@ -9936,6 +9936,502 @@ void btrfs_set_range_writeback(struct extent_io_tree *tree, u64 start, u64 end)
> > }
> > }
> > +static int encoded_iov_compression_from_btrfs(unsigned int compress_type)
> > +{
> > + switch (compress_type) {
> > + case BTRFS_COMPRESS_NONE:
> > + return ENCODED_IOV_COMPRESSION_NONE;
> > + case BTRFS_COMPRESS_ZLIB:
> > + return ENCODED_IOV_COMPRESSION_BTRFS_ZLIB;
> > + case BTRFS_COMPRESS_LZO:
> > + /*
> > + * The LZO format depends on the page size. 64k is the maximum
> > + * sectorsize (and thus page size) that we support.
> > + */
> > + if (PAGE_SIZE < SZ_4K || PAGE_SIZE > SZ_64K)
> > + return -EINVAL;
> > + return ENCODED_IOV_COMPRESSION_BTRFS_LZO_4K + (PAGE_SHIFT - 12);
> > + case BTRFS_COMPRESS_ZSTD:
> > + return ENCODED_IOV_COMPRESSION_BTRFS_ZSTD;
> > + default:
> > + return -EUCLEAN;
> > + }
> > +}
> > +
> > +static ssize_t btrfs_encoded_read_inline(struct kiocb *iocb,
> > + struct iov_iter *iter, u64 start,
> > + u64 lockend,
> > + struct extent_state **cached_state,
> > + u64 extent_start, size_t count,
> > + struct encoded_iov *encoded,
> > + bool *unlocked)
> > +{
> > + struct inode *inode = file_inode(iocb->ki_filp);
> > + struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
> > + struct btrfs_path *path;
> > + struct extent_buffer *leaf;
> > + struct btrfs_file_extent_item *item;
> > + u64 ram_bytes;
> > + unsigned long ptr;
> > + void *tmp;
> > + ssize_t ret;
> > +
> > + path = btrfs_alloc_path();
> > + if (!path) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> > + ret = btrfs_lookup_file_extent(NULL, BTRFS_I(inode)->root, path,
> > + btrfs_ino(BTRFS_I(inode)), extent_start,
> > + 0);
> > + if (ret) {
> > + if (ret > 0) {
> > + /* The extent item disappeared? */
> > + ret = -EIO;
> > + }
> > + goto out;
> > + }
> > + leaf = path->nodes[0];
> > + item = btrfs_item_ptr(leaf, path->slots[0],
> > + struct btrfs_file_extent_item);
> > +
> > + ram_bytes = btrfs_file_extent_ram_bytes(leaf, item);
> > + ptr = btrfs_file_extent_inline_start(item);
> > +
> > + encoded->len = (min_t(u64, extent_start + ram_bytes, inode->i_size) -
> > + iocb->ki_pos);
> > + ret = encoded_iov_compression_from_btrfs(
> > + btrfs_file_extent_compression(leaf, item));
> > + if (ret < 0)
> > + goto out;
> > + encoded->compression = ret;
> > + if (encoded->compression) {
> > + size_t inline_size;
> > +
> > + inline_size = btrfs_file_extent_inline_item_len(leaf,
> > + btrfs_item_nr(path->slots[0]));
> > + if (inline_size > count) {
> > + ret = -ENOBUFS;
> > + goto out;
> > + }
> > + count = inline_size;
> > + encoded->unencoded_len = ram_bytes;
> > + encoded->unencoded_offset = iocb->ki_pos - extent_start;
> > + } else {
> > + encoded->len = encoded->unencoded_len = count =
> > + min_t(u64, count, encoded->len);
> > + ptr += iocb->ki_pos - extent_start;
> > + }
> > +
> > + tmp = kmalloc(count, GFP_NOFS);
> > + if (!tmp) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> > + read_extent_buffer(leaf, tmp, ptr, count);
> > + btrfs_release_path(path);
> > + unlock_extent_cached(io_tree, start, lockend, cached_state);
> > + inode_unlock_shared(inode);
> > + *unlocked = true;
> > +
> > + ret = copy_encoded_iov_to_iter(encoded, iter);
> > + if (ret)
> > + goto out_free;
> > + ret = copy_to_iter(tmp, count, iter);
> > + if (ret != count)
> > + ret = -EFAULT;
> > +out_free:
> > + kfree(tmp);
> > +out:
> > + btrfs_free_path(path);
> > + return ret;
> > +}
> > +
> > +struct btrfs_encoded_read_private {
> > + struct inode *inode;
> > + wait_queue_head_t wait;
> > + atomic_t pending;
> > + blk_status_t status;
> > + bool skip_csum;
> > +};
> > +
> > +static blk_status_t submit_encoded_read_bio(struct inode *inode,
> > + struct bio *bio, int mirror_num,
> > + unsigned long bio_flags)
> > +{
> > + struct btrfs_encoded_read_private *priv = bio->bi_private;
> > + struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
> > + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > + blk_status_t ret;
> > +
> > + if (!priv->skip_csum) {
> > + ret = btrfs_lookup_bio_sums(inode, bio, io_bio->logical, NULL);
> > + if (ret)
> > + return ret;
> > + }
> > +
> > + ret = btrfs_bio_wq_end_io(fs_info, bio, BTRFS_WQ_ENDIO_DATA);
> > + if (ret) {
> > + btrfs_io_bio_free_csum(io_bio);
> > + return ret;
> > + }
> > +
> > + atomic_inc(&priv->pending);
> > + ret = btrfs_map_bio(fs_info, bio, mirror_num);
> > + if (ret) {
> > + atomic_dec(&priv->pending);
> > + btrfs_io_bio_free_csum(io_bio);
> > + }
> > + return ret;
> > +}
> > +
> > +static blk_status_t btrfs_encoded_read_check_bio(struct btrfs_io_bio *io_bio)
> > +{
> > + const bool uptodate = io_bio->bio.bi_status == BLK_STS_OK;
> > + struct btrfs_encoded_read_private *priv = io_bio->bio.bi_private;
> > + struct inode *inode = priv->inode;
> > + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > + u32 sectorsize = fs_info->sectorsize;
> > + struct bio_vec *bvec;
> > + struct bvec_iter_all iter_all;
> > + u64 start = io_bio->logical;
> > + int icsum = 0;
> > +
> > + if (priv->skip_csum || !uptodate)
> > + return io_bio->bio.bi_status;
> > +
> > + bio_for_each_segment_all(bvec, &io_bio->bio, iter_all) {
> > + unsigned int i, nr_sectors, pgoff;
> > +
> > + nr_sectors = BTRFS_BYTES_TO_BLKS(fs_info, bvec->bv_len);
> > + pgoff = bvec->bv_offset;
> > + for (i = 0; i < nr_sectors; i++) {
> > + ASSERT(pgoff < PAGE_SIZE);
> > + if (check_data_csum(inode, io_bio, icsum, bvec->bv_page,
> > + pgoff, start))
> > + return BLK_STS_IOERR;
> > + start += sectorsize;
> > + icsum++;
> > + pgoff += sectorsize;
> > + }
> > + }
> > + return BLK_STS_OK;
> > +}
> > +
> > +static void btrfs_encoded_read_endio(struct bio *bio)
> > +{
> > + struct btrfs_encoded_read_private *priv = bio->bi_private;
> > + struct btrfs_io_bio *io_bio = btrfs_io_bio(bio);
> > + blk_status_t status;
> > +
> > + status = btrfs_encoded_read_check_bio(io_bio);
> > + if (status) {
> > + /*
> > + * The memory barrier implied by the atomic_dec_return() here
> > + * pairs with the memory barrier implied by the
> > + * atomic_dec_return() or io_wait_event() in
> > + * btrfs_encoded_read_regular_fill_pages() to ensure that this
> > + * write is observed before the load of status in
> > + * btrfs_encoded_read_regular_fill_pages().
> > + */
> > + WRITE_ONCE(priv->status, status);
> > + }
> > + if (!atomic_dec_return(&priv->pending))
> > + wake_up(&priv->wait);
> > + btrfs_io_bio_free_csum(io_bio);
> > + bio_put(bio);
> > +}
> > +
> > +static int btrfs_encoded_read_regular_fill_pages(struct inode *inode, u64 offset,
> > + u64 disk_io_size, struct page **pages)
> > +{
> > + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > + struct btrfs_encoded_read_private priv = {
> > + .inode = inode,
> > + .pending = ATOMIC_INIT(1),
> > + .skip_csum = BTRFS_I(inode)->flags & BTRFS_INODE_NODATASUM,
> > + };
> > + unsigned long i = 0;
> > + u64 cur = 0;
> > + int ret;
> > +
> > + init_waitqueue_head(&priv.wait);
> > + /*
> > + * Submit bios for the extent, splitting due to bio or stripe limits as
> > + * necessary.
> > + */
> > + while (cur < disk_io_size) {
> > + struct btrfs_io_geometry geom;
> > + struct bio *bio = NULL;
> > + u64 remaining;
> > +
> > + ret = btrfs_get_io_geometry(fs_info, BTRFS_MAP_READ,
> > + offset + cur, disk_io_size - cur,
> > + &geom);
> > + if (ret) {
> > + WRITE_ONCE(priv.status, errno_to_blk_status(ret));
> > + break;
> > + }
> > + remaining = min(geom.len, disk_io_size - cur);
> > + while (bio || remaining) {
> > + size_t bytes = min_t(u64, remaining, PAGE_SIZE);
> > +
> > + if (!bio) {
> > + bio = btrfs_bio_alloc(offset + cur);
> > + bio->bi_end_io = btrfs_encoded_read_endio;
> > + bio->bi_private = &priv;
> > + bio->bi_opf = REQ_OP_READ;
> > + }
> > +
> > + if (!bytes ||
> > + bio_add_page(bio, pages[i], bytes, 0) < bytes) {
> > + blk_status_t status;
> > +
> > + status = submit_encoded_read_bio(inode, bio, 0,
> > + 0);
> > + if (status) {
> > + WRITE_ONCE(priv.status, status);
> > + bio_put(bio);
> > + goto out;
> > + }
> > + bio = NULL;
> > + continue;
> > + }
> > +
> > + i++;
> > + cur += bytes;
> > + remaining -= bytes;
> > + }
> > + }
> > +
> > +out:
> > + if (atomic_dec_return(&priv.pending))
> > + io_wait_event(priv.wait, !atomic_read(&priv.pending));
> > + /* See btrfs_encoded_read_endio() for ordering. */
> > + return blk_status_to_errno(READ_ONCE(priv.status));
> > +}
> > +
> > +static ssize_t btrfs_encoded_read_regular(struct kiocb *iocb,
> > + struct iov_iter *iter,
> > + u64 start, u64 lockend,
> > + struct extent_state **cached_state,
> > + u64 offset, u64 disk_io_size,
> > + size_t count,
> > + const struct encoded_iov *encoded,
> > + bool *unlocked)
> > +{
> > + struct inode *inode = file_inode(iocb->ki_filp);
> > + struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
> > + struct page **pages;
> > + unsigned long nr_pages, i;
> > + u64 cur;
> > + size_t page_offset;
> > + ssize_t ret;
> > +
> > + nr_pages = DIV_ROUND_UP(disk_io_size, PAGE_SIZE);
> > + pages = kcalloc(nr_pages, sizeof(struct page *), GFP_NOFS);
> > + if (!pages)
> > + return -ENOMEM;
> > + for (i = 0; i < nr_pages; i++) {
> > + pages[i] = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
> > + if (!pages[i]) {
> > + ret = -ENOMEM;
> > + goto out;
> > + }
> > + }
> > +
> > + ret = btrfs_encoded_read_regular_fill_pages(inode, offset, disk_io_size,
> > + pages);
> > + if (ret)
> > + goto out;
> > +
> > + unlock_extent_cached(io_tree, start, lockend, cached_state);
> > + inode_unlock_shared(inode);
> > + *unlocked = true;
> > +
> > + ret = copy_encoded_iov_to_iter(encoded, iter);
> > + if (ret)
> > + goto out;
> > + if (encoded->compression) {
> > + i = 0;
> > + page_offset = 0;
> > + } else {
> > + i = (iocb->ki_pos - start) >> PAGE_SHIFT;
> > + page_offset = (iocb->ki_pos - start) & (PAGE_SIZE - 1);
> > + }
> > + cur = 0;
> > + while (cur < count) {
> > + size_t bytes = min_t(size_t, count - cur,
> > + PAGE_SIZE - page_offset);
> > +
> > + if (copy_page_to_iter(pages[i], page_offset, bytes,
> > + iter) != bytes) {
> > + ret = -EFAULT;
> > + goto out;
> > + }
> > + i++;
> > + cur += bytes;
> > + page_offset = 0;
> > + }
> > + ret = count;
> > +out:
> > + for (i = 0; i < nr_pages; i++) {
> > + if (pages[i])
> > + __free_page(pages[i]);
> > + }
> > + kfree(pages);
> > + return ret;
> > +}
> > +
> > +ssize_t btrfs_encoded_read(struct kiocb *iocb, struct iov_iter *iter)
> > +{
> > + struct inode *inode = file_inode(iocb->ki_filp);
> > + struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
> > + struct extent_io_tree *io_tree = &BTRFS_I(inode)->io_tree;
> > + ssize_t ret;
> > + size_t count;
> > + u64 start, lockend, offset, disk_io_size;
> > + struct extent_state *cached_state = NULL;
> > + struct extent_map *em;
> > + struct encoded_iov encoded = {};
> > + bool unlocked = false;
> > +
> > + ret = generic_encoded_read_checks(iocb, iter);
> > + if (ret < 0)
> > + return ret;
> > + if (ret == 0)
> > + return copy_encoded_iov_to_iter(&encoded, iter);
> > + count = ret;
> > +
> > + file_accessed(iocb->ki_filp);
> > +
> > + inode_lock_shared(inode);
> > +
> > + if (iocb->ki_pos >= inode->i_size) {
> > + inode_unlock_shared(inode);
> > + return copy_encoded_iov_to_iter(&encoded, iter);
> > + }
> > + start = ALIGN_DOWN(iocb->ki_pos, fs_info->sectorsize);
> > + /*
> > + * We don't know how long the extent containing iocb->ki_pos is, but if
> > + * it's compressed we know that it won't be longer than this.
> > + */
> > + lockend = start + BTRFS_MAX_UNCOMPRESSED - 1;
> > +
> > + for (;;) {
> > + struct btrfs_ordered_extent *ordered;
> > +
> > + ret = btrfs_wait_ordered_range(inode, start,
> > + lockend - start + 1);
> > + if (ret)
> > + goto out_unlock_inode;
> > + lock_extent_bits(io_tree, start, lockend, &cached_state);
> > + ordered = btrfs_lookup_ordered_range(BTRFS_I(inode), start,
> > + lockend - start + 1);
> > + if (!ordered)
> > + break;
> > + btrfs_put_ordered_extent(ordered);
> > + unlock_extent_cached(io_tree, start, lockend, &cached_state);
> > + cond_resched();
> > + }
>
> This can be replaced with btrfs_lock_and_flush_ordered_range(). Then you can add
Sorry, finally getting back to this after the break. Please correct me
if I'm wrong, but I don't think btrfs_lock_and_flush_ordered_range() is
strong enough here.
An encoded read needs to make sure that any buffered writes are on disk
(since it's basically direct I/O). btrfs_lock_and_flush_ordered_range()
bails immediately if there aren't any ordered extents. As far as I can
tell, ordered extents aren't created until writepage, so if I do some
buffered writes and call btrfs_lock_and_flush_ordered_range() before
writepage creates the ordered extents, it won't flush the buffered
writes like I need it to. This loop with btrfs_wait_ordered_range()
does.
