Re: [PATCH v4 2/2] NFSD: Simplify READ_PLUS

[Jeff Layton <jlayton@kernel.org>]

On Tue, 2022-09-13 at 14:01 -0400, Anna Schumaker wrote:
> From: Anna Schumaker <Anna.Schumaker@Netapp.com>
> 
> Chuck had suggested reverting READ_PLUS so it returns a single DATA
> segment covering the requested read range. This prepares the server for
> a future "sparse read" function so support can easily be added without
> needing to rip out the old READ_PLUS code at the same time.
> 
> Signed-off-by: Anna Schumaker <Anna.Schumaker@Netapp.com>
> ---
>  fs/nfsd/nfs4xdr.c | 139 +++++++++++-----------------------------------
>  1 file changed, 32 insertions(+), 107 deletions(-)
> 
> diff --git a/fs/nfsd/nfs4xdr.c b/fs/nfsd/nfs4xdr.c
> index 01dd73ed5720..280c7c8ac807 100644
> --- a/fs/nfsd/nfs4xdr.c
> +++ b/fs/nfsd/nfs4xdr.c
> @@ -4731,79 +4731,37 @@ nfsd4_encode_offload_status(struct nfsd4_compoundres *resp, __be32 nfserr,
>  
>  static __be32
>  nfsd4_encode_read_plus_data(struct nfsd4_compoundres *resp,
> -			    struct nfsd4_read *read,
> -			    unsigned long *maxcount, u32 *eof,
> -			    loff_t *pos)
> +			    struct nfsd4_read *read)
>  {
> -	struct xdr_stream *xdr = resp->xdr;
> +	bool splice_ok = test_bit(RQ_SPLICE_OK, &resp->rqstp->rq_flags);
>  	struct file *file = read->rd_nf->nf_file;
> -	int starting_len = xdr->buf->len;
> -	loff_t hole_pos;
> -	__be32 nfserr;
> -	__be32 *p, tmp;
> -	__be64 tmp64;
> -
> -	hole_pos = pos ? *pos : vfs_llseek(file, read->rd_offset, SEEK_HOLE);
> -	if (hole_pos > read->rd_offset)
> -		*maxcount = min_t(unsigned long, *maxcount, hole_pos - read->rd_offset);
> -	*maxcount = min_t(unsigned long, *maxcount, (xdr->buf->buflen - xdr->buf->len));
> +	struct xdr_stream *xdr = resp->xdr;
> +	unsigned long maxcount;
> +	__be32 nfserr, *p;
>  
>  	/* Content type, offset, byte count */
>  	p = xdr_reserve_space(xdr, 4 + 8 + 4);
>  	if (!p)
> -		return nfserr_resource;
> +		return nfserr_io;
> +	if (resp->xdr->buf->page_len && splice_ok) {
> +		WARN_ON_ONCE(splice_ok);
> +		return nfserr_serverfault;
> +	}
>  
> -	read->rd_vlen = xdr_reserve_space_vec(xdr, resp->rqstp->rq_vec, *maxcount);
> -	if (read->rd_vlen < 0)
> -		return nfserr_resource;
> +	maxcount = min_t(unsigned long, read->rd_length,
> +			 (xdr->buf->buflen - xdr->buf->len));
>  
> -	nfserr = nfsd_readv(resp->rqstp, read->rd_fhp, file, read->rd_offset,
> -			    resp->rqstp->rq_vec, read->rd_vlen, maxcount, eof);
> +	if (file->f_op->splice_read && splice_ok)
> +		nfserr = nfsd4_encode_splice_read(resp, read, file, maxcount);
> +	else
> +		nfserr = nfsd4_encode_readv(resp, read, file, maxcount);
>  	if (nfserr)
>  		return nfserr;
> -	xdr_truncate_encode(xdr, starting_len + 16 + xdr_align_size(*maxcount));
>  
> -	tmp = htonl(NFS4_CONTENT_DATA);
> -	write_bytes_to_xdr_buf(xdr->buf, starting_len,      &tmp,   4);
> -	tmp64 = cpu_to_be64(read->rd_offset);
> -	write_bytes_to_xdr_buf(xdr->buf, starting_len + 4,  &tmp64, 8);
> -	tmp = htonl(*maxcount);
> -	write_bytes_to_xdr_buf(xdr->buf, starting_len + 12, &tmp,   4);
> -
> -	tmp = xdr_zero;
> -	write_bytes_to_xdr_buf(xdr->buf, starting_len + 16 + *maxcount, &tmp,
> -			       xdr_pad_size(*maxcount));
> -	return nfs_ok;
> -}
> -
> -static __be32
> -nfsd4_encode_read_plus_hole(struct nfsd4_compoundres *resp,
> -			    struct nfsd4_read *read,
> -			    unsigned long *maxcount, u32 *eof)
> -{
> -	struct file *file = read->rd_nf->nf_file;
> -	loff_t data_pos = vfs_llseek(file, read->rd_offset, SEEK_DATA);
> -	loff_t f_size = i_size_read(file_inode(file));
> -	unsigned long count;
> -	__be32 *p;
> -
> -	if (data_pos == -ENXIO)
> -		data_pos = f_size;
> -	else if (data_pos <= read->rd_offset || (data_pos < f_size && data_pos % PAGE_SIZE))
> -		return nfsd4_encode_read_plus_data(resp, read, maxcount, eof, &f_size);
> -	count = data_pos - read->rd_offset;
> -
> -	/* Content type, offset, byte count */
> -	p = xdr_reserve_space(resp->xdr, 4 + 8 + 8);
> -	if (!p)
> -		return nfserr_resource;
> -
> -	*p++ = htonl(NFS4_CONTENT_HOLE);
> +	*p++ = cpu_to_be32(NFS4_CONTENT_DATA);
>  	p = xdr_encode_hyper(p, read->rd_offset);
> -	p = xdr_encode_hyper(p, count);
> +	*p = cpu_to_be32(read->rd_length);
>  
> -	*eof = (read->rd_offset + count) >= f_size;
> -	*maxcount = min_t(unsigned long, count, *maxcount);
>  	return nfs_ok;
>  }
>  
> @@ -4811,69 +4769,36 @@ static __be32
>  nfsd4_encode_read_plus(struct nfsd4_compoundres *resp, __be32 nfserr,
>  		       struct nfsd4_read *read)
>  {
> -	unsigned long maxcount, count;
> +	struct file *file = read->rd_nf->nf_file;
>  	struct xdr_stream *xdr = resp->xdr;
> -	struct file *file;
>  	int starting_len = xdr->buf->len;
> -	int last_segment = xdr->buf->len;
> -	int segments = 0;
> -	__be32 *p, tmp;
> -	bool is_data;
> -	loff_t pos;
> -	u32 eof;
> +	u32 segments = 0;
> +	__be32 *p;
>  
>  	if (nfserr)
>  		return nfserr;
> -	file = read->rd_nf->nf_file;
>  
>  	/* eof flag, segment count */
>  	p = xdr_reserve_space(xdr, 4 + 4);
>  	if (!p)
> -		return nfserr_resource;
> +		return nfserr_io;
>  	xdr_commit_encode(xdr);
>  
> -	maxcount = min_t(unsigned long, read->rd_length,
> -			 (xdr->buf->buflen - xdr->buf->len));
> -	count    = maxcount;
> -
> -	eof = read->rd_offset >= i_size_read(file_inode(file));
> -	if (eof)
> +	read->rd_eof = read->rd_offset >= i_size_read(file_inode(file));
> +	if (read->rd_eof)
>  		goto out;
>  
> -	pos = vfs_llseek(file, read->rd_offset, SEEK_HOLE);
> -	is_data = pos > read->rd_offset;
> -
> -	while (count > 0 && !eof) {
> -		maxcount = count;
> -		if (is_data)
> -			nfserr = nfsd4_encode_read_plus_data(resp, read, &maxcount, &eof,
> -						segments == 0 ? &pos : NULL);
> -		else
> -			nfserr = nfsd4_encode_read_plus_hole(resp, read, &maxcount, &eof);
> -		if (nfserr)
> -			goto out;
> -		count -= maxcount;
> -		read->rd_offset += maxcount;
> -		is_data = !is_data;
> -		last_segment = xdr->buf->len;
> -		segments++;
> -	}
> -
> -out:
> -	if (nfserr && segments == 0)
> +	nfserr = nfsd4_encode_read_plus_data(resp, read);
> +	if (nfserr) {
>  		xdr_truncate_encode(xdr, starting_len);
> -	else {
> -		if (nfserr) {
> -			xdr_truncate_encode(xdr, last_segment);
> -			nfserr = nfs_ok;
> -			eof = 0;
> -		}
> -		tmp = htonl(eof);
> -		write_bytes_to_xdr_buf(xdr->buf, starting_len,     &tmp, 4);
> -		tmp = htonl(segments);
> -		write_bytes_to_xdr_buf(xdr->buf, starting_len + 4, &tmp, 4);
> +		return nfserr;
>  	}
>  
> +	segments++;
> +
> +out:
> +	p = xdr_encode_bool(p, read->rd_eof);
> +	*p = cpu_to_be32(segments);
>  	return nfserr;
>  }
>  

Reviewed-by: Jeff Layton <jlayton@kernel.org>