iov.h

   1 /*
   2  * Helpers for using (partial) iovecs.
   3  *
   4  * Copyright (C) 2010 Red Hat, Inc.
   5  *
   6  * Author(s):
   7  *  Amit Shah <amit.shah@redhat.com>
   8  *  Michael Tokarev <mjt@tls.msk.ru>
   9  *
  10  * This work is licensed under the terms of the GNU GPL, version 2.  See
  11  * the COPYING file in the top-level directory.
  12  */
  13
  14 #include "qemu-common.h"
  15
  16 /**
  17  * count and return data size, in bytes, of an iovec
  18  * starting at `iov' of `iov_cnt' number of elements.
  19  */
  20 size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
  21
  22 /**
  23  * Copy from single continuous buffer to scatter-gather vector of buffers
  24  * (iovec) and back like memcpy() between two continuous memory regions.
  25  * Data in single continuous buffer starting at address `buf' and
  26  * `bytes' bytes long will be copied to/from an iovec `iov' with
  27  * `iov_cnt' number of elements, starting at byte position `offset'
  28  * within the iovec.  If the iovec does not contain enough space,
  29  * only part of data will be copied, up to the end of the iovec.
  30  * Number of bytes actually copied will be returned, which is
  31  *  min(bytes, iov_size(iov)-offset)
  32  * `Offset' must point to the inside of iovec.
  33  * It is okay to use very large value for `bytes' since we're
  34  * limited by the size of the iovec anyway, provided that the
  35  * buffer pointed to by buf has enough space.  One possible
  36  * such "large" value is -1 (sinice size_t is unsigned),
  37  * so specifying `-1' as `bytes' means 'up to the end of iovec'.
  38  */
  39 size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
  40                     size_t offset, const void *buf, size_t bytes);
  41 size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
  42                   size_t offset, void *buf, size_t bytes);
  43
  44 /**
  45  * Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
  46  * starting at byte offset `start', to value `fillc', repeating it
  47  * `bytes' number of times.  `Offset' must point to the inside of iovec.
  48  * If `bytes' is large enough, only last bytes portion of iovec,
  49  * up to the end of it, will be filled with the specified value.
  50  * Function return actual number of bytes processed, which is
  51  * min(size, iov_size(iov) - offset).
  52  * Again, it is okay to use large value for `bytes' to mean "up to the end".
  53  */
  54 size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
  55                   size_t offset, int fillc, size_t bytes);
  56
  57 /*
  58  * Send/recv data from/to iovec buffers directly
  59  *
  60  * `offset' bytes in the beginning of iovec buffer are skipped and
  61  * next `bytes' bytes are used, which must be within data of iovec.
  62  *
  63  *   r = iov_send_recv(sockfd, iov, iovcnt, offset, bytes, true);
  64  *
  65  * is logically equivalent to
  66  *
  67  *   char *buf = malloc(bytes);
  68  *   iov_to_buf(iov, iovcnt, offset, buf, bytes);
  69  *   r = send(sockfd, buf, bytes, 0);
  70  *   free(buf);
  71  *
  72  * For iov_send_recv() _whole_ area being sent or received
  73  * should be within the iovec, not only beginning of it.
  74  */
  75 ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
  76                       size_t offset, size_t bytes, bool do_send);
  77 #define iov_recv(sockfd, iov, iov_cnt, offset, bytes) \
  78   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, false)
  79 #define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
  80   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
  81
  82 /**
  83  * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
  84  * in file `fp', prefixing each line with `prefix' and processing not more
  85  * than `limit' data bytes.
  86  */
  87 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
  88                  FILE *fp, const char *prefix, size_t limit);
  89
  90 /*
  91  * Partial copy of vector from iov to dst_iov (data is not copied).
  92  * dst_iov overlaps iov at a specified offset.
  93  * size of dst_iov is at most bytes. dst vector count is returned.
  94  */
  95 unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
  96                  const struct iovec *iov, unsigned int iov_cnt,
  97                  size_t offset, size_t bytes);