SOCKET use readv/writev to write directly into iovectors

This patch adds support for read/writev to directly read and write
from/to iovectors. Before this patch on read and write from/to socket
the operation was limited by the iovec boundaries. If there is enough
data in the buffer or enough buffer space available its now possible
to transfer the whole data in one atomic operaion.

Signed-off-by: Peter Lieven <pl@kamp.de>

lib/socket.c

@@ -42,6 +42,7 @@
 #include <string.h>
 #include <errno.h>
 #include <fcntl.h>
+#include "scsi-lowlevel.h"
 #include "iscsi.h"
 #include "iscsi-private.h"
 #include "slist.h"
@@ -363,6 +364,91 @@ iscsi_queue_length(struct iscsi_context *iscsi)
 	return i;
 }
 
+ssize_t
+iscsi_iovector_readv_writev(struct iscsi_context *iscsi, struct scsi_iovector *iovector, uint32_t pos, ssize_t max_read, int do_write)
+{
+	if (iovector->iov == NULL) {
+		errno = EINVAL;
+		return -1;
+	}
+
+	if (pos < iovector->offset) {
+		/* start over in case we are going backwards */
+		iovector->offset = 0;
+		iovector->consumed = 0;
+	}
+
+	if (iovector->niov <= iovector->consumed) {
+		/* someone issued a read/write but did not provide enough user buffers for all the data.
+		 * maybe someone tried to read just 512 bytes off a MMC device?
+		 */
+		errno = EINVAL;
+		return -1;
+	}
+
+	/* iov is a pointer to the first iovec to pass */
+	struct scsi_iovec *iov = &iovector->iov[iovector->consumed];
+	pos -= iovector->offset;
+
+	/* forward until iov points to the first iov to pass */
+	while (pos >= iov->iov_len) {
+		iovector->offset += iov->iov_len;
+		iovector->consumed++;
+		pos -= iov->iov_len;
+		if (iovector->niov <= iovector->consumed) {
+			errno = EINVAL;
+			return -1;
+		}
+		iov = &iovector->iov[iovector->consumed];
+	}
+
+	/* iov2 is a pointer to the last iovec to pass */
+	struct scsi_iovec *iov2 = iov;
+
+	int niov=1; /* number of iovectors to pass */
+	uint32_t len2 = pos + max_read; /* adjust length of iov2 */
+	
+	/* forward until iov2 points to the last iovec we pass later. it might
+	   happen that we have a lot of iovectors but are limited by max_read */
+	while (len2 > iov2->iov_len) {
+		if (iovector->niov <= iovector->consumed+niov-1) {
+			errno = EINVAL;
+			return -1;
+		}
+		niov++;
+		len2 -= iov2->iov_len;
+		iov2 = &iovector->iov[iovector->consumed+niov-1];
+	}
+
+	/* we might limit the length of the last iovec we pass to readv/writev
+	   store its orignal length to restore it later */
+	size_t _len2 = iov2->iov_len;
+
+	/* adjust base+len of start iovec and len of last iovec */
+	iov2->iov_len = len2;
+	iov->iov_base = (void*) ((uintptr_t)iov->iov_base + pos);
+	iov->iov_len -= pos;
+
+	ssize_t n;
+	if (do_write) {
+		n = writev(iscsi->fd, (struct iovec*) iov, niov);
+	} else {
+		n = readv(iscsi->fd, (struct iovec*) iov, niov);
+	}
+
+	/* restore original values */
+	iov->iov_base = (void*) ((uintptr_t)iov->iov_base - pos);
+	iov->iov_len += pos;
+	iov2->iov_len = _len2;
+
+	if (n > max_read) {
+		/* we read/write more bytes than expected, this MUST not happen */
+		errno = EINVAL;
+		return -1;
+	}
+	return n;
+}
+
 static int
 iscsi_read_from_socket(struct iscsi_context *iscsi)
 {
@@ -411,13 +497,16 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
 	}
 	if (data_size != 0) {
 		unsigned char *buf = NULL;
+		struct scsi_iovector * iovector_in;
 
 		count = data_size - in->data_pos;
 
 		/* first try to see if we already have a user buffer */
-		buf = iscsi_get_user_in_buffer(iscsi, in, in->data_pos, &count);
-		/* if not, allocate one */
-		if (buf == NULL) {
+		iovector_in = iscsi_get_scsi_task_iovector_in(iscsi, in);
+		if (iovector_in != NULL) {
+			uint32_t offset = scsi_get_uint32(&in->hdr[40]);
+			count = iscsi_iovector_readv_writev(iscsi, iovector_in, in->data_pos + offset, count, 0);
+		} else {
 			if (in->data == NULL) {
 				in->data = iscsi_malloc(iscsi, data_size);
 				if (in->data == NULL) {
@@ -426,9 +515,9 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
 				}
 			}
 			buf = &in->data[in->data_pos];
+			count = recv(iscsi->fd, buf, count, 0);
 		}
-
-		count = recv(iscsi->fd, buf, count, 0);
+		
 		if (count == 0) {
 			return -1;
 		}
@@ -440,6 +529,7 @@ iscsi_read_from_socket(struct iscsi_context *iscsi)
 				"errno:%d", errno);
 			return -1;
 		}
+
 		in->data_pos += count;
 	}
 
@@ -524,19 +614,17 @@ iscsi_write_to_socket(struct iscsi_context *iscsi)
 
 		/* Write any iovectors that might have been passed to us */
 		while (pdu->out_written < pdu->out_len) {
-			unsigned char *buf;
+			struct scsi_iovector* iovector_out;
 
-			count = pdu->out_len - pdu->out_written;
-			buf = iscsi_get_user_out_buffer(iscsi, pdu, pdu->out_offset + pdu->out_written, &count);
-			if (buf == NULL) {
+			iovector_out = iscsi_get_scsi_task_iovector_out(iscsi, pdu);
+
+			if (iovector_out == NULL) {
 				iscsi_set_error(iscsi, "Can't find iovector data for DATA-OUT");
 				return -1;
 			}
 
-			count = send(iscsi->fd,
-				     buf,
-				     count,
-				     0);
+			count = iscsi_iovector_readv_writev(iscsi, iovector_out, pdu->out_offset + pdu->out_written, pdu->out_len - pdu->out_written, 1);
+
 			if (count == -1) {
 				if (errno == EAGAIN || errno == EWOULDBLOCK) {
 					return 0;
@@ -545,6 +633,7 @@ iscsi_write_to_socket(struct iscsi_context *iscsi)
 						"socket :%d", errno);
 				return -1;
 			}
+
 			pdu->out_written += count;
 		}