Merge pull request #127 from plieven/revert_iovector

Revert "Rewrite and simplify iscsi_iovector_readv_writev"

include/scsi-lowlevel.h

@@ -270,9 +270,8 @@ struct scsi_iovector {
 	struct scsi_iovec *iov;
 	int niov;
 	int nalloc;
-
-	size_t reserved_1;
-	int reserved_2;
+	size_t offset;
+	int consumed;
 };
 
 struct scsi_task {

lib/socket.c

@@ -410,82 +410,89 @@ iscsi_queue_length(struct iscsi_context *iscsi)
 	return i;
 }
 
-static ssize_t
-iscsi_iovector_readv_writev(struct iscsi_context *iscsi, struct scsi_iovector *iovector, uint32_t pos, size_t count, int do_write)
+ssize_t
+iscsi_iovector_readv_writev(struct iscsi_context *iscsi, struct scsi_iovector *iovector, uint32_t pos, ssize_t max_read, int do_write)
 {
-	struct iovec *iovs;
-	struct iovec *first_iov;
-	struct iovec *last_iov;
-	int i, niov;
-	size_t skip_first, skip_last;
-
 	if (iovector->iov == NULL) {
 		errno = EINVAL;
 		return -1;
 	}
 
-	niov = iovector->niov;
-	iovs = alloca(sizeof(struct iovec) * niov);
-	if (iovs == NULL) {
-		errno = ENOMEM;
+	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;
 	}
-	for(i = 0; i < niov; i++) {
-		iovs[i].iov_base = iovector->iov[i].iov_base;
-		iovs[i].iov_len  = iovector->iov[i].iov_len;
-	}
 
-	first_iov = &iovs[0];
+	/* iov is a pointer to the first iovec to pass */
+	struct scsi_iovec *iov = &iovector->iov[iovector->consumed];
+	pos -= iovector->offset;
 
-	/* Step past iovectors until we find the first iov to send */
-	while (pos >= first_iov->iov_len) {
-		pos -= first_iov->iov_len;
-		first_iov++;
-		niov--;
-		if (niov <= 0) {
-			/* We ran out of iovectors. */
+	/* 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;
 		}
-	}
-	/* How many bytes in the first iov to skip */
-	skip_first = pos;
-	if (skip_first > 0) {
-		char *buf = first_iov->iov_base;
-		first_iov->iov_base  = &buf[skip_first];
-		first_iov->iov_len  -= skip_first;
+		iov = &iovector->iov[iovector->consumed];
 	}
 
+	/* iov2 is a pointer to the last iovec to pass */
+	struct scsi_iovec *iov2 = iov;
 
-	/* Find the last iovector to send */
-	last_iov = first_iov;
-	while (count >last_iov->iov_len) {
-		count -= last_iov->iov_len;
-		last_iov++;
-		niov--;
-		if (niov <= 0) {
-			/* We ran out of iovectors. */
+	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;
 		}
-	}
-	/* How many bytes in the last iov to skip */
-	skip_last = last_iov->iov_len - count;
-	if (skip_last > 0) {
-		last_iov->iov_len  -= skip_last;
+		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;
 
-	/* number of iovectors we will be using */
-	niov = last_iov - first_iov + 1;
+	/* 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) {
-		count = writev(iscsi->fd, first_iov, niov);
+		n = writev(iscsi->fd, (struct iovec*) iov, niov);
 	} else {
-		count = readv(iscsi->fd, first_iov, niov);
+		n = readv(iscsi->fd, (struct iovec*) iov, niov);
 	}
 
-	return count;
+	/* 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