Re: [PATCH v21 22/30] ocfs2: Provide a splice-read stub

Joseph Qi
2023-05-22T02:49:41Z

On 5/20/23 8:00 AM, David Howells wrote:
> Provide a splice_read stub for ocfs2. This emits trace lines and does an
> atime lock/update before calling filemap_splice_read(). Splicing from
> direct I/O is handled by the caller.
>
> A couple of new tracepoints are added for this purpose.
>
> 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: Mark Fasheh <mark@fasheh.com>
> cc: Joel Becker <jlbec@evilplan.org>
> cc: Joseph Qi <joseph.qi@linux.alibaba.com>
> cc: ocfs2-devel@oss.oracle.com
> cc: linux-fsdevel@vger.kernel.org
> cc: linux-block@vger.kernel.org
> cc: linux-mm@kvack.org
> ---
> fs/ocfs2/file.c | 39 ++++++++++++++++++++++++++++++++++++++-
> fs/ocfs2/ocfs2_trace.h | 3 +++
> 2 files changed, 41 insertions(+), 1 deletion(-)
>
> diff --git a/fs/ocfs2/file.c b/fs/ocfs2/file.c
> index efb09de4343d..f7e00b5689d5 100644
> --- a/fs/ocfs2/file.c
> +++ b/fs/ocfs2/file.c
> @@ -2581,6 +2581,43 @@ static ssize_t ocfs2_file_read_iter(struct kiocb *iocb,
> return ret;
> }
>
> +static ssize_t ocfs2_file_splice_read(struct file *in, loff_t *ppos,
> + struct pipe_inode_info *pipe,
> + size_t len, unsigned int flags)
> +{
> + struct inode *inode = file_inode(in);
> + ssize_t ret = 0;
> + int lock_level = 0;
> +
> + trace_ocfs2_file_splice_read(inode, in, in->f_path.dentry,
> + (unsigned long long)OCFS2_I(inode)->ip_blkno,
> + in->f_path.dentry->d_name.len,
> + in->f_path.dentry->d_name.name,
> + 0);

Better also trace flags here.

> +
> + /*
> + * We're fine letting folks race truncates and extending writes with
> + * read across the cluster, just like they can locally. Hence no
> + * rw_lock during read.
> + *
> + * Take and drop the meta data lock to update inode fields like i_size.
> + * This allows the checks down below generic_file_splice_read() a

Now it calls filemap_splice_read().

> + * chance of actually working.
> + */
> + ret = ocfs2_inode_lock_atime(inode, in->f_path.mnt, &lock_level, true);

Since prototype is 'int wait', so directly passing '1' seems more appropriate.

> + if (ret < 0) {
> + if (ret != -EAGAIN)
> + mlog_errno(ret);
> + goto bail;
> + }
> + ocfs2_inode_unlock(inode, lock_level);
> +

Don't see direct IO logic now. Am I missing something?

Thanks,
Joseph

> + ret = filemap_splice_read(in, ppos, pipe, len, flags);
> + trace_filemap_splice_read_ret(ret);
> +bail:
> + return ret;
> +}
> +
> /* Refer generic_file_llseek_unlocked() */
> static loff_t ocfs2_file_llseek(struct file *file, loff_t offset, int whence)
> {
> @@ -2744,7 +2781,7 @@ const struct file_operations ocfs2_fops = {
> #endif
> .lock = ocfs2_lock,
> .flock = ocfs2_flock,
> - .splice_read = generic_file_splice_read,
> + .splice_read = ocfs2_file_splice_read,
> .splice_write = iter_file_splice_write,
> .fallocate = ocfs2_fallocate,
> .remap_file_range = ocfs2_remap_file_range,
> diff --git a/fs/ocfs2/ocfs2_trace.h b/fs/ocfs2/ocfs2_trace.h
> index dc4bce1649c1..b8c3d1702076 100644
> --- a/fs/ocfs2/ocfs2_trace.h
> +++ b/fs/ocfs2/ocfs2_trace.h
> @@ -1319,6 +1319,8 @@ DEFINE_OCFS2_FILE_OPS(ocfs2_file_splice_write);
>
> DEFINE_OCFS2_FILE_OPS(ocfs2_file_read_iter);
>
> +DEFINE_OCFS2_FILE_OPS(ocfs2_file_splice_read);
> +
> DEFINE_OCFS2_ULL_ULL_ULL_EVENT(ocfs2_truncate_file);
>
> DEFINE_OCFS2_ULL_ULL_EVENT(ocfs2_truncate_file_error);
> @@ -1470,6 +1472,7 @@ TRACE_EVENT(ocfs2_prepare_inode_for_write,
> );
>
> DEFINE_OCFS2_INT_EVENT(generic_file_read_iter_ret);
> +DEFINE_OCFS2_INT_EVENT(filemap_splice_read_ret);
>
> /* End of trace events for fs/ocfs2/file.c. */
>