iov.c - qemu - Git at Google

 /*
  * Helpers for getting linearized buffers from iov / filling buffers into iovs
  *
  * Copyright IBM, Corp. 2007, 2008
  * Copyright (C) 2010 Red Hat, Inc.
  *
  * Author(s):
  *  Anthony Liguori <aliguori@us.ibm.com>
  *  Amit Shah <amit.shah@redhat.com>
  *  Michael Tokarev <mjt@tls.msk.ru>
  *
  * This work is licensed under the terms of the GNU GPL, version 2.  See
  * the COPYING file in the top-level directory.
  *
  * Contributions after 2012-01-13 are licensed under the terms of the
  * GNU GPL, version 2 or (at your option) any later version.
  */

 #include "qemu/iov.h"

 #ifdef _WIN32
 # include <windows.h>
 # include <winsock2.h>
 #else
 # include <sys/types.h>
 # include <sys/socket.h>
 #endif

 size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
                     size_t offset, const void *buf, size_t bytes)
 {
     size_t done;
     unsigned int i;
     for (i = 0, done = 0; (offset || done < bytes) && i < iov_cnt; i++) {
         if (offset < iov[i].iov_len) {
             size_t len = MIN(iov[i].iov_len - offset, bytes - done);
             memcpy(iov[i].iov_base + offset, buf + done, len);
             done += len;
             offset = 0;
         } else {
             offset -= iov[i].iov_len;
         }
     }
     assert(offset == 0);
     return done;
 }

 size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
                   size_t offset, void *buf, size_t bytes)
 {
     size_t done;
     unsigned int i;
     for (i = 0, done = 0; (offset || done < bytes) && i < iov_cnt; i++) {
         if (offset < iov[i].iov_len) {
             size_t len = MIN(iov[i].iov_len - offset, bytes - done);
             memcpy(buf + done, iov[i].iov_base + offset, len);
             done += len;
             offset = 0;
         } else {
             offset -= iov[i].iov_len;
         }
     }
     assert(offset == 0);
     return done;
 }

 size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
                   size_t offset, int fillc, size_t bytes)
 {
     size_t done;
     unsigned int i;
     for (i = 0, done = 0; (offset || done < bytes) && i < iov_cnt; i++) {
         if (offset < iov[i].iov_len) {
             size_t len = MIN(iov[i].iov_len - offset, bytes - done);
             memset(iov[i].iov_base + offset, fillc, len);
             done += len;
             offset = 0;
         } else {
             offset -= iov[i].iov_len;
         }
     }
     assert(offset == 0);
     return done;
 }

 size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt)
 {
     size_t len;
     unsigned int i;

     len = 0;
     for (i = 0; i < iov_cnt; i++) {
         len += iov[i].iov_len;
     }
     return len;
 }

 /* helper function for iov_send_recv() */
 static ssize_t
 do_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, bool do_send)
 {
 #if defined CONFIG_IOVEC && defined CONFIG_POSIX
     ssize_t ret;
     struct msghdr msg;
     memset(&msg, 0, sizeof(msg));
     msg.msg_iov = iov;
     msg.msg_iovlen = iov_cnt;
     do {
         ret = do_send
             ? sendmsg(sockfd, &msg, 0)
             : recvmsg(sockfd, &msg, 0);
     } while (ret < 0 && errno == EINTR);
     return ret;
 #else
     /* else send piece-by-piece */
     /*XXX Note: windows has WSASend() and WSARecv() */
     unsigned i = 0;
     ssize_t ret = 0;
     while (i < iov_cnt) {
         ssize_t r = do_send
             ? send(sockfd, iov[i].iov_base, iov[i].iov_len, 0)
             : recv(sockfd, iov[i].iov_base, iov[i].iov_len, 0);
         if (r > 0) {
             ret += r;
         } else if (!r) {
             break;
         } else if (errno == EINTR) {
             continue;
         } else {
             /* else it is some "other" error,
              * only return if there was no data processed. */
             if (ret == 0) {
                 ret = -1;
             }
             break;
         }
         i++;
     }
     return ret;
 #endif
 }

 ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
                       size_t offset, size_t bytes,
                       bool do_send)
 {
     ssize_t ret;
     unsigned si, ei;            /* start and end indexes */
     if (bytes == 0) {
         /* Catch the do-nothing case early, as otherwise we will pass an
          * empty iovec to sendmsg/recvmsg(), and not all implementations
          * accept this.
          */
         return 0;
     }

     /* Find the start position, skipping `offset' bytes:
      * first, skip all full-sized vector elements, */
     for (si = 0; si < iov_cnt && offset >= iov[si].iov_len; ++si) {
         offset -= iov[si].iov_len;
     }
     if (offset) {
         assert(si < iov_cnt);
         /* second, skip `offset' bytes from the (now) first element,
          * undo it on exit */
         iov[si].iov_base += offset;
         iov[si].iov_len -= offset;
     }
     /* Find the end position skipping `bytes' bytes: */
     /* first, skip all full-sized elements */
     for (ei = si; ei < iov_cnt && iov[ei].iov_len <= bytes; ++ei) {
         bytes -= iov[ei].iov_len;
     }
     if (bytes) {
         /* second, fixup the last element, and remember
          * the length we've cut from the end of it in `bytes' */
         size_t tail;
         assert(ei < iov_cnt);
         assert(iov[ei].iov_len > bytes);
         tail = iov[ei].iov_len - bytes;
         iov[ei].iov_len = bytes;
         bytes = tail;  /* bytes is now equal to the tail size */
         ++ei;
     }

     ret = do_send_recv(sockfd, iov + si, ei - si, do_send);

     /* Undo the changes above */
     if (offset) {
         iov[si].iov_base -= offset;
         iov[si].iov_len += offset;
     }
     if (bytes) {
         iov[ei-1].iov_len += bytes;
     }

     return ret;
 }


 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
                  FILE *fp, const char *prefix, size_t limit)
 {
     unsigned int i, v, b;
     uint8_t *c;

     c = iov[0].iov_base;
     for (i = 0, v = 0, b = 0; b < limit; i++, b++) {
         if (i == iov[v].iov_len) {
             i = 0; v++;
             if (v == iov_cnt) {
                 break;
             }
             c = iov[v].iov_base;
         }
         if ((b % 16) == 0) {
             fprintf(fp, "%s: %04x:", prefix, b);
         }
         if ((b % 4) == 0) {
             fprintf(fp, " ");
         }
         fprintf(fp, " %02x", c[i]);
         if ((b % 16) == 15) {
             fprintf(fp, "\n");
         }
     }
     if ((b % 16) != 0) {
         fprintf(fp, "\n");
     }
 }

 unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
                  const struct iovec *iov, unsigned int iov_cnt,
                  size_t offset, size_t bytes)
 {
     size_t len;
     unsigned int i, j;
     for (i = 0, j = 0; i < iov_cnt && j < dst_iov_cnt && bytes; i++) {
         if (offset >= iov[i].iov_len) {
             offset -= iov[i].iov_len;
             continue;
         }
         len = MIN(bytes, iov[i].iov_len - offset);

         dst_iov[j].iov_base = iov[i].iov_base + offset;
         dst_iov[j].iov_len = len;
         j++;
         bytes -= len;
         offset = 0;
     }
     assert(offset == 0);
     return j;
 }

 /* io vectors */

 void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint)
 {
     qiov->iov = g_malloc(alloc_hint * sizeof(struct iovec));
     qiov->niov = 0;
     qiov->nalloc = alloc_hint;
     qiov->size = 0;
 }

 void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov)
 {
     int i;

     qiov->iov = iov;
     qiov->niov = niov;
     qiov->nalloc = -1;
     qiov->size = 0;
     for (i = 0; i < niov; i++)
         qiov->size += iov[i].iov_len;
 }

 void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len)
 {
     assert(qiov->nalloc != -1);

     if (qiov->niov == qiov->nalloc) {
         qiov->nalloc = 2 * qiov->nalloc + 1;
         qiov->iov = g_realloc(qiov->iov, qiov->nalloc * sizeof(struct iovec));
     }
     qiov->iov[qiov->niov].iov_base = base;
     qiov->iov[qiov->niov].iov_len = len;
     qiov->size += len;
     ++qiov->niov;
 }

 /*
  * Concatenates (partial) iovecs from src_iov to the end of dst.
  * It starts copying after skipping `soffset' bytes at the
  * beginning of src and adds individual vectors from src to
  * dst copies up to `sbytes' bytes total, or up to the end
  * of src_iov if it comes first.  This way, it is okay to specify
  * very large value for `sbytes' to indicate "up to the end
  * of src".
  * Only vector pointers are processed, not the actual data buffers.
  */
 void qemu_iovec_concat_iov(QEMUIOVector *dst,
                            struct iovec *src_iov, unsigned int src_cnt,
                            size_t soffset, size_t sbytes)
 {
     int i;
     size_t done;
     assert(dst->nalloc != -1);
     for (i = 0, done = 0; done < sbytes && i < src_cnt; i++) {
         if (soffset < src_iov[i].iov_len) {
             size_t len = MIN(src_iov[i].iov_len - soffset, sbytes - done);
             qemu_iovec_add(dst, src_iov[i].iov_base + soffset, len);
             done += len;
             soffset = 0;
         } else {
             soffset -= src_iov[i].iov_len;
         }
     }
     assert(soffset == 0); /* offset beyond end of src */
 }

 /*
  * Concatenates (partial) iovecs from src to the end of dst.
  * It starts copying after skipping `soffset' bytes at the
  * beginning of src and adds individual vectors from src to
  * dst copies up to `sbytes' bytes total, or up to the end
  * of src if it comes first.  This way, it is okay to specify
  * very large value for `sbytes' to indicate "up to the end
  * of src".
  * Only vector pointers are processed, not the actual data buffers.
  */
 void qemu_iovec_concat(QEMUIOVector *dst,
                        QEMUIOVector *src, size_t soffset, size_t sbytes)
 {
     qemu_iovec_concat_iov(dst, src->iov, src->niov, soffset, sbytes);
 }

 void qemu_iovec_destroy(QEMUIOVector *qiov)
 {
     assert(qiov->nalloc != -1);

     qemu_iovec_reset(qiov);
     g_free(qiov->iov);
     qiov->nalloc = 0;
     qiov->iov = NULL;
 }

 void qemu_iovec_reset(QEMUIOVector *qiov)
 {
     assert(qiov->nalloc != -1);

     qiov->niov = 0;
     qiov->size = 0;
 }

 size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
                          void *buf, size_t bytes)
 {
     return iov_to_buf(qiov->iov, qiov->niov, offset, buf, bytes);
 }

 size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
                            const void *buf, size_t bytes)
 {
     return iov_from_buf(qiov->iov, qiov->niov, offset, buf, bytes);
 }

 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
                          int fillc, size_t bytes)
 {
     return iov_memset(qiov->iov, qiov->niov, offset, fillc, bytes);
 }

 size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
                          size_t bytes)
 {
     size_t total = 0;
     struct iovec *cur;

     for (cur = *iov; *iov_cnt > 0; cur++) {
         if (cur->iov_len > bytes) {
             cur->iov_base += bytes;
             cur->iov_len -= bytes;
             total += bytes;
             break;
         }

         bytes -= cur->iov_len;
         total += cur->iov_len;
         *iov_cnt -= 1;
     }

     *iov = cur;
     return total;
 }

 size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
                         size_t bytes)
 {
     size_t total = 0;
     struct iovec *cur;

     if (*iov_cnt == 0) {
         return 0;
     }

     cur = iov + (*iov_cnt - 1);

     while (*iov_cnt > 0) {
         if (cur->iov_len > bytes) {
             cur->iov_len -= bytes;
             total += bytes;
             break;
         }

         bytes -= cur->iov_len;
         total += cur->iov_len;
         cur--;
         *iov_cnt -= 1;
     }

     return total;
 }
	/*
	* Helpers for getting linearized buffers from iov / filling buffers into iovs
	*
	* Copyright IBM, Corp. 2007, 2008
	* Copyright (C) 2010 Red Hat, Inc.
	*
	* Author(s):
	* Anthony Liguori <aliguori@us.ibm.com>
	* Amit Shah <amit.shah@redhat.com>
	* Michael Tokarev <mjt@tls.msk.ru>
	*
	* This work is licensed under the terms of the GNU GPL, version 2. See
	* the COPYING file in the top-level directory.
	*
	* Contributions after 2012-01-13 are licensed under the terms of the
	* GNU GPL, version 2 or (at your option) any later version.
	*/

	#include "qemu/iov.h"

	#ifdef _WIN32
	# include <windows.h>
	# include <winsock2.h>
	#else
	# include <sys/types.h>
	# include <sys/socket.h>
	#endif

	size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
	size_t offset, const void *buf, size_t bytes)
	{
	size_t done;
	unsigned int i;
	for (i = 0, done = 0; (offset \|\| done < bytes) && i < iov_cnt; i++) {
	if (offset < iov[i].iov_len) {
	size_t len = MIN(iov[i].iov_len - offset, bytes - done);
	memcpy(iov[i].iov_base + offset, buf + done, len);
	done += len;
	offset = 0;
	} else {
	offset -= iov[i].iov_len;
	}
	}
	assert(offset == 0);
	return done;
	}

	size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
	size_t offset, void *buf, size_t bytes)
	{
	size_t done;
	unsigned int i;
	for (i = 0, done = 0; (offset \|\| done < bytes) && i < iov_cnt; i++) {
	if (offset < iov[i].iov_len) {
	size_t len = MIN(iov[i].iov_len - offset, bytes - done);
	memcpy(buf + done, iov[i].iov_base + offset, len);
	done += len;
	offset = 0;
	} else {
	offset -= iov[i].iov_len;
	}
	}
	assert(offset == 0);
	return done;
	}

	size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
	size_t offset, int fillc, size_t bytes)
	{
	size_t done;
	unsigned int i;
	for (i = 0, done = 0; (offset \|\| done < bytes) && i < iov_cnt; i++) {
	if (offset < iov[i].iov_len) {
	size_t len = MIN(iov[i].iov_len - offset, bytes - done);
	memset(iov[i].iov_base + offset, fillc, len);
	done += len;
	offset = 0;
	} else {
	offset -= iov[i].iov_len;
	}
	}
	assert(offset == 0);
	return done;
	}

	size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt)
	{
	size_t len;
	unsigned int i;

	len = 0;
	for (i = 0; i < iov_cnt; i++) {
	len += iov[i].iov_len;
	}
	return len;
	}

	/* helper function for iov_send_recv() */
	static ssize_t
	do_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt, bool do_send)
	{
	#if defined CONFIG_IOVEC && defined CONFIG_POSIX
	ssize_t ret;
	struct msghdr msg;
	memset(&msg, 0, sizeof(msg));
	msg.msg_iov = iov;
	msg.msg_iovlen = iov_cnt;
	do {
	ret = do_send
	? sendmsg(sockfd, &msg, 0)
	: recvmsg(sockfd, &msg, 0);
	} while (ret < 0 && errno == EINTR);
	return ret;
	#else
	/* else send piece-by-piece */
	/XXX Note: windows has WSASend() and WSARecv() /
	unsigned i = 0;
	ssize_t ret = 0;
	while (i < iov_cnt) {
	ssize_t r = do_send
	? send(sockfd, iov[i].iov_base, iov[i].iov_len, 0)
	: recv(sockfd, iov[i].iov_base, iov[i].iov_len, 0);
	if (r > 0) {
	ret += r;
	} else if (!r) {
	break;
	} else if (errno == EINTR) {
	continue;
	} else {
	/* else it is some "other" error,
	* only return if there was no data processed. */
	if (ret == 0) {
	ret = -1;
	}
	break;
	}
	i++;
	}
	return ret;
	#endif
	}

	ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
	size_t offset, size_t bytes,
	bool do_send)
	{
	ssize_t ret;
	unsigned si, ei; /* start and end indexes */
	if (bytes == 0) {
	/* Catch the do-nothing case early, as otherwise we will pass an
	* empty iovec to sendmsg/recvmsg(), and not all implementations
	* accept this.
	*/
	return 0;
	}

	/* Find the start position, skipping `offset' bytes:
	* first, skip all full-sized vector elements, */
	for (si = 0; si < iov_cnt && offset >= iov[si].iov_len; ++si) {
	offset -= iov[si].iov_len;
	}
	if (offset) {
	assert(si < iov_cnt);
	/* second, skip `offset' bytes from the (now) first element,
	* undo it on exit */
	iov[si].iov_base += offset;
	iov[si].iov_len -= offset;
	}
	/* Find the end position skipping `bytes' bytes: */
	/* first, skip all full-sized elements */
	for (ei = si; ei < iov_cnt && iov[ei].iov_len <= bytes; ++ei) {
	bytes -= iov[ei].iov_len;
	}
	if (bytes) {
	/* second, fixup the last element, and remember
	* the length we've cut from the end of it in `bytes' */
	size_t tail;
	assert(ei < iov_cnt);
	assert(iov[ei].iov_len > bytes);
	tail = iov[ei].iov_len - bytes;
	iov[ei].iov_len = bytes;
	bytes = tail; /* bytes is now equal to the tail size */
	++ei;
	}

	ret = do_send_recv(sockfd, iov + si, ei - si, do_send);

	/* Undo the changes above */
	if (offset) {
	iov[si].iov_base -= offset;
	iov[si].iov_len += offset;
	}
	if (bytes) {
	iov[ei-1].iov_len += bytes;
	}

	return ret;
	}


	void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
	FILE fp, const char prefix, size_t limit)
	{
	unsigned int i, v, b;
	uint8_t *c;

	c = iov[0].iov_base;
	for (i = 0, v = 0, b = 0; b < limit; i++, b++) {
	if (i == iov[v].iov_len) {
	i = 0; v++;
	if (v == iov_cnt) {
	break;
	}
	c = iov[v].iov_base;
	}
	if ((b % 16) == 0) {
	fprintf(fp, "%s: %04x:", prefix, b);
	}
	if ((b % 4) == 0) {
	fprintf(fp, " ");
	}
	fprintf(fp, " %02x", c[i]);
	if ((b % 16) == 15) {
	fprintf(fp, "\n");
	}
	}
	if ((b % 16) != 0) {
	fprintf(fp, "\n");
	}
	}

	unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
	const struct iovec *iov, unsigned int iov_cnt,
	size_t offset, size_t bytes)
	{
	size_t len;
	unsigned int i, j;
	for (i = 0, j = 0; i < iov_cnt && j < dst_iov_cnt && bytes; i++) {
	if (offset >= iov[i].iov_len) {
	offset -= iov[i].iov_len;
	continue;
	}
	len = MIN(bytes, iov[i].iov_len - offset);

	dst_iov[j].iov_base = iov[i].iov_base + offset;
	dst_iov[j].iov_len = len;
	j++;
	bytes -= len;
	offset = 0;
	}
	assert(offset == 0);
	return j;
	}

	/* io vectors */

	void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint)
	{
	qiov->iov = g_malloc(alloc_hint * sizeof(struct iovec));
	qiov->niov = 0;
	qiov->nalloc = alloc_hint;
	qiov->size = 0;
	}

	void qemu_iovec_init_external(QEMUIOVector qiov, struct iovec iov, int niov)
	{
	int i;

	qiov->iov = iov;
	qiov->niov = niov;
	qiov->nalloc = -1;
	qiov->size = 0;
	for (i = 0; i < niov; i++)
	qiov->size += iov[i].iov_len;
	}

	void qemu_iovec_add(QEMUIOVector qiov, void base, size_t len)
	{
	assert(qiov->nalloc != -1);

	if (qiov->niov == qiov->nalloc) {
	qiov->nalloc = 2 * qiov->nalloc + 1;
	qiov->iov = g_realloc(qiov->iov, qiov->nalloc * sizeof(struct iovec));
	}
	qiov->iov[qiov->niov].iov_base = base;
	qiov->iov[qiov->niov].iov_len = len;
	qiov->size += len;
	++qiov->niov;
	}

	/*
	* Concatenates (partial) iovecs from src_iov to the end of dst.
	* It starts copying after skipping `soffset' bytes at the
	* beginning of src and adds individual vectors from src to
	* dst copies up to `sbytes' bytes total, or up to the end
	* of src_iov if it comes first. This way, it is okay to specify
	* very large value for `sbytes' to indicate "up to the end
	* of src".
	* Only vector pointers are processed, not the actual data buffers.
	*/
	void qemu_iovec_concat_iov(QEMUIOVector *dst,
	struct iovec *src_iov, unsigned int src_cnt,
	size_t soffset, size_t sbytes)
	{
	int i;
	size_t done;
	assert(dst->nalloc != -1);
	for (i = 0, done = 0; done < sbytes && i < src_cnt; i++) {
	if (soffset < src_iov[i].iov_len) {
	size_t len = MIN(src_iov[i].iov_len - soffset, sbytes - done);
	qemu_iovec_add(dst, src_iov[i].iov_base + soffset, len);
	done += len;
	soffset = 0;
	} else {
	soffset -= src_iov[i].iov_len;
	}
	}
	assert(soffset == 0); /* offset beyond end of src */
	}

	/*
	* Concatenates (partial) iovecs from src to the end of dst.
	* It starts copying after skipping `soffset' bytes at the
	* beginning of src and adds individual vectors from src to
	* dst copies up to `sbytes' bytes total, or up to the end
	* of src if it comes first. This way, it is okay to specify
	* very large value for `sbytes' to indicate "up to the end
	* of src".
	* Only vector pointers are processed, not the actual data buffers.
	*/
	void qemu_iovec_concat(QEMUIOVector *dst,
	QEMUIOVector *src, size_t soffset, size_t sbytes)
	{
	qemu_iovec_concat_iov(dst, src->iov, src->niov, soffset, sbytes);
	}

	void qemu_iovec_destroy(QEMUIOVector *qiov)
	{
	assert(qiov->nalloc != -1);

	qemu_iovec_reset(qiov);
	g_free(qiov->iov);
	qiov->nalloc = 0;
	qiov->iov = NULL;
	}

	void qemu_iovec_reset(QEMUIOVector *qiov)
	{
	assert(qiov->nalloc != -1);

	qiov->niov = 0;
	qiov->size = 0;
	}

	size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
	void *buf, size_t bytes)
	{
	return iov_to_buf(qiov->iov, qiov->niov, offset, buf, bytes);
	}

	size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
	const void *buf, size_t bytes)
	{
	return iov_from_buf(qiov->iov, qiov->niov, offset, buf, bytes);
	}

	size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
	int fillc, size_t bytes)
	{
	return iov_memset(qiov->iov, qiov->niov, offset, fillc, bytes);
	}

	size_t iov_discard_front(struct iovec *iov, unsigned int iov_cnt,
	size_t bytes)
	{
	size_t total = 0;
	struct iovec *cur;

	for (cur = iov; iov_cnt > 0; cur++) {
	if (cur->iov_len > bytes) {
	cur->iov_base += bytes;
	cur->iov_len -= bytes;
	total += bytes;
	break;
	}

	bytes -= cur->iov_len;
	total += cur->iov_len;
	*iov_cnt -= 1;
	}

	*iov = cur;
	return total;
	}

	size_t iov_discard_back(struct iovec iov, unsigned int iov_cnt,
	size_t bytes)
	{
	size_t total = 0;
	struct iovec *cur;

	if (*iov_cnt == 0) {
	return 0;
	}

	cur = iov + (*iov_cnt - 1);

	while (*iov_cnt > 0) {
	if (cur->iov_len > bytes) {
	cur->iov_len -= bytes;
	total += bytes;
	break;
	}

	bytes -= cur->iov_len;
	total += cur->iov_len;
	cur--;
	*iov_cnt -= 1;
	}

	return total;
	}