Re: [PATCH v21 16/30] ceph: Provide a splice-read stub

Xiubo Li
2023-05-22T02:13:08Z

On 5/20/23 08:00, David Howells wrote:
> Provide a splice_read stub for Ceph. This does the inode shutdown check
> before proceeding and jumps to copy_splice_read() if the file has inline
> data or is a synchronous file.
>
> We try and get FILE_RD and either FILE_CACHE and/or FILE_LAZYIO caps and
> hold them across filemap_splice_read(). If we fail to get FILE_CACHE or
> FILE_LAZYIO capabilities, we use copy_splice_read() instead.
>
> Signed-off-by: David Howells <dhowells@redhat.com>
> cc: Christoph Hellwig <hch@lst.de>
> cc: Al Viro <viro@zeniv.linux.org.uk>
> cc: Jens Axboe <axboe@kernel.dk>
> cc: Xiubo Li <xiubli@redhat.com>
> cc: Ilya Dryomov <idryomov@gmail.com>
> cc: Jeff Layton <jlayton@kernel.org>
> cc: ceph-devel@vger.kernel.org
> cc: linux-fsdevel@vger.kernel.org
> cc: linux-block@vger.kernel.org
> cc: linux-mm@kvack.org
> ---
>
> Notes:
> ver #21)
> - Need to drop the caps ref.
> - O_DIRECT is handled by the caller.
>
> fs/ceph/file.c | 65 +++++++++++++++++++++++++++++++++++++++++++++++++-
> 1 file changed, 64 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ceph/file.c b/fs/ceph/file.c
> index f4d8bf7dec88..4285f6cb5d3b 100644
> --- a/fs/ceph/file.c
> +++ b/fs/ceph/file.c
> @@ -1745,6 +1745,69 @@ static ssize_t ceph_read_iter(struct kiocb *iocb, struct iov_iter *to)
> return ret;
> }
>
> +/*
> + * Wrap filemap_splice_read with checks for cap bits on the inode.
> + * Atomically grab references, so that those bits are not released
> + * back to the MDS mid-read.
> + */
> +static ssize_t ceph_splice_read(struct file *in, loff_t *ppos,
> + struct pipe_inode_info *pipe,
> + size_t len, unsigned int flags)
> +{
> + struct ceph_file_info *fi = in->private_data;
> + struct inode *inode = file_inode(in);
> + struct ceph_inode_info *ci = ceph_inode(inode);
> + ssize_t ret;
> + int want = 0, got = 0;
> + CEPH_DEFINE_RW_CONTEXT(rw_ctx, 0);
> +
> + dout("splice_read %p %llx.%llx %llu~%zu trying to get caps on %p\n",
> + inode, ceph_vinop(inode), *ppos, len, inode);
> +
> + if (ceph_inode_is_shutdown(inode))
> + return -ESTALE;
> +
> + if (ceph_has_inline_data(ci) ||
> + (fi->flags & CEPH_F_SYNC))
> + return copy_splice_read(in, ppos, pipe, len, flags);
> +
> + ceph_start_io_read(inode);
> +
> + want = CEPH_CAP_FILE_CACHE;
> + if (fi->fmode & CEPH_FILE_MODE_LAZY)
> + want |= CEPH_CAP_FILE_LAZYIO;
> +
> + ret = ceph_get_caps(in, CEPH_CAP_FILE_RD, want, -1, &got);
> + if (ret < 0)
> + goto out_end;
> +
> + if ((got & (CEPH_CAP_FILE_CACHE | CEPH_CAP_FILE_LAZYIO)) == 0) {
> + dout("splice_read/sync %p %llx.%llx %llu~%zu got cap refs on %s\n",
> + inode, ceph_vinop(inode), *ppos, len,
> + ceph_cap_string(got));
> +
> + ceph_put_cap_refs(ci, got);
> + ceph_end_io_read(inode);
> + return copy_splice_read(in, ppos, pipe, len, flags);
> + }
> +
> + dout("splice_read %p %llx.%llx %llu~%zu got cap refs on %s\n",
> + inode, ceph_vinop(inode), *ppos, len, ceph_cap_string(got));
> +
> + rw_ctx.caps = got;
> + ceph_add_rw_context(fi, &rw_ctx);
> + ret = filemap_splice_read(in, ppos, pipe, len, flags);
> + ceph_del_rw_context(fi, &rw_ctx);
> +
> + dout("splice_read %p %llx.%llx dropping cap refs on %s = %zd\n",
> + inode, ceph_vinop(inode), ceph_cap_string(got), ret);
> +
> + ceph_put_cap_refs(ci, got);
> +out_end:
> + ceph_end_io_read(inode);
> + return ret;
> +}
> +
> /*
> * Take cap references to avoid releasing caps to MDS mid-write.
> *
> @@ -2593,7 +2656,7 @@ const struct file_operations ceph_file_fops = {
> .lock = ceph_lock,
> .setlease = simple_nosetlease,
> .flock = ceph_flock,
> - .splice_read = generic_file_splice_read,
> + .splice_read = ceph_splice_read,
> .splice_write = iter_file_splice_write,
> .unlocked_ioctl = ceph_ioctl,
> .compat_ioctl = compat_ptr_ioctl,
>
LGTM.

Reviewed-by: Xiubo Li <xiubli@redhat.com>

Thanks

- Xiubo