Re: [RFC-V3 6/7] [net/9p] Read and Write side zerocopy changes for 9P2000.L protocol.

["Aneesh Kumar K. V" <aneesh.kumar@linux.vnet.ibm.com>]

On Thu, 10 Feb 2011 17:25:10 -0800, "Venkateswararao Jujjuri (JV)" <jvrao@linux.vnet.ibm.com> wrote:
> Signed-off-by: Venkateswararao Jujjuri <jvrao@linux.vnet.ibm.com>
> ---
>  net/9p/client.c   |   47 +++++++++++++++++++++++++++++++++--------------
>  net/9p/protocol.c |   21 +++++++++++++++++++++
>  2 files changed, 54 insertions(+), 14 deletions(-)
> 
> diff --git a/net/9p/client.c b/net/9p/client.c
> index a848bca..f6d8531 100644
> --- a/net/9p/client.c
> +++ b/net/9p/client.c
> @@ -1270,7 +1270,15 @@ p9_client_read(struct p9_fid *fid, char *data, char __user *udata, u64 offset,
>  	if (count < rsize)
>  		rsize = count;
> 
> -	req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset, rsize);
> +	/* Don't bother zerocopy form small IO (< 1024) */
> +	if (((clnt->trans_mod->pref & P9_TRANS_PREF_PAYLOAD_MASK) ==
> +			P9_TRANS_PREF_PAYLOAD_SEP) && (rsize > 1024)) {
> +		req = p9_client_rpc(clnt, P9_TREAD, "dqE", fid->fid, offset,
> +				rsize, data, udata);
> +	} else {
> +		req = p9_client_rpc(clnt, P9_TREAD, "dqd", fid->fid, offset,
> +				rsize);
> +	}
>  	if (IS_ERR(req)) {
>  		err = PTR_ERR(req);
>  		goto error;
> @@ -1284,13 +1292,15 @@ p9_client_read(struct p9_fid *fid, char *data, char __user *udata, u64 offset,
> 
>  	P9_DPRINTK(P9_DEBUG_9P, "<<< RREAD count %d\n", count);
> 
> -	if (data) {
> -		memmove(data, dataptr, count);
> -	} else {
> -		err = copy_to_user(udata, dataptr, count);
> -		if (err) {
> -			err = -EFAULT;
> -			goto free_and_error;
> +	if (!req->tc->pbuf_size) {
> +		if (data) {
> +			memmove(data, dataptr, count);
> +		} else {
> +			err = copy_to_user(udata, dataptr, count);
> +			if (err) {
> +				err = -EFAULT;
> +				goto free_and_error;
> +			}
>  		}
>  	}
>  	p9_free_req(clnt, req);
> @@ -1323,12 +1333,21 @@ p9_client_write(struct p9_fid *fid, char *data, const char __user *udata,
> 
>  	if (count < rsize)
>  		rsize = count;
> -	if (data)
> -		req = p9_client_rpc(clnt, P9_TWRITE, "dqD", fid->fid, offset,
> -								rsize, data);
> -	else
> -		req = p9_client_rpc(clnt, P9_TWRITE, "dqU", fid->fid, offset,
> -								rsize, udata);
> +
> +	/* Don't bother zerocopy form small IO (< 1024) */
> +	if (((clnt->trans_mod->pref & P9_TRANS_PREF_PAYLOAD_MASK) ==
> +			P9_TRANS_PREF_PAYLOAD_SEP) && (rsize > 1024)) {
> +		req = p9_client_rpc(clnt, P9_TWRITE, "dqE", fid->fid, offset,
> +				rsize, data, udata);
> +	} else {
> +		if (data)
> +			req = p9_client_rpc(clnt, P9_TWRITE, "dqD", fid->fid,
> +					offset, rsize, data);
> +		else
> +			req = p9_client_rpc(clnt, P9_TWRITE, "dqU", fid->fid,
> +					offset, rsize, udata);
> +	}
> +
>  	if (IS_ERR(req)) {
>  		err = PTR_ERR(req);
>  		goto error;
> diff --git a/net/9p/protocol.c b/net/9p/protocol.c
> index 5936c50..830b999 100644
> --- a/net/9p/protocol.c
> +++ b/net/9p/protocol.c
> @@ -114,6 +114,17 @@ pdu_write_u(struct p9_fcall *pdu, const char __user *udata, size_t size)
>  	return size - len;
>  }
> 
> +static size_t
> +pdu_write_urw(struct p9_fcall *pdu, const char *kdata, const char __user *udata,
> +		size_t size)
> +{
> +	size_t len = min(pdu->capacity - pdu->size, size);

Why do we need to do this ? We are not placing anything in the pdu right ?

> +	pdu->pubuf = (char __user *)udata;
> +	pdu->pkbuf = (char *)kdata;
> +	pdu->pbuf_size = len;
> +	return size - len;

Does this mean a zero copy write of a buffer larger than msize will
result in a failure ?

> +}
> +
>  /*
>  	b - int8_t
>  	w - int16_t
> @@ -445,6 +456,16 @@ p9pdu_vwritef(struct p9_fcall *pdu, int proto_version, const char *fmt,
>  					errcode = -EFAULT;
>  			}
>  			break;
> +		case 'E':{
> +				 int32_t cnt = va_arg(ap, int32_t);
> +				 const char *k = va_arg(ap, const void *);
> +				 const char *u = va_arg(ap, const void *);
> +				 errcode = p9pdu_writef(pdu, proto_version, "d",
> +						 cnt);
> +				 if (!errcode && pdu_write_urw(pdu, k, u, cnt))
> +					errcode = -EFAULT;
> +			 }
> +			 break;
>  		case 'U':{
>  				int32_t count = va_arg(ap, int32_t);
>  				const char __user *udata =


-aneesh