include/qemu/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 #ifndef IOV_H
  15 #define IOV_H
  16
  17 #include "qemu-common.h"
  18
  19 /**
  20  * count and return data size, in bytes, of an iovec
  21  * starting at `iov' of `iov_cnt' number of elements.
  22  */
  23 size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
  24
  25 /**
  26  * Copy from single continuous buffer to scatter-gather vector of buffers
  27  * (iovec) and back like memcpy() between two continuous memory regions.
  28  * Data in single continuous buffer starting at address `buf' and
  29  * `bytes' bytes long will be copied to/from an iovec `iov' with
  30  * `iov_cnt' number of elements, starting at byte position `offset'
  31  * within the iovec.  If the iovec does not contain enough space,
  32  * only part of data will be copied, up to the end of the iovec.
  33  * Number of bytes actually copied will be returned, which is
  34  *  min(bytes, iov_size(iov)-offset)
  35  * `Offset' must point to the inside of iovec.
  36  * It is okay to use very large value for `bytes' since we're
  37  * limited by the size of the iovec anyway, provided that the
  38  * buffer pointed to by buf has enough space.  One possible
  39  * such "large" value is -1 (sinice size_t is unsigned),
  40  * so specifying `-1' as `bytes' means 'up to the end of iovec'.
  41  */
  42 size_t iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
  43                     size_t offset, const void *buf, size_t bytes);
  44 size_t iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
  45                   size_t offset, void *buf, size_t bytes);
  46
  47 /**
  48  * Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
  49  * starting at byte offset `start', to value `fillc', repeating it
  50  * `bytes' number of times.  `Offset' must point to the inside of iovec.
  51  * If `bytes' is large enough, only last bytes portion of iovec,
  52  * up to the end of it, will be filled with the specified value.
  53  * Function return actual number of bytes processed, which is
  54  * min(size, iov_size(iov) - offset).
  55  * Again, it is okay to use large value for `bytes' to mean "up to the end".
  56  */
  57 size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
  58                   size_t offset, int fillc, size_t bytes);
  59
  60 /*
  61  * Send/recv data from/to iovec buffers directly
  62  *
  63  * `offset' bytes in the beginning of iovec buffer are skipped and
  64  * next `bytes' bytes are used, which must be within data of iovec.
  65  *
  66  *   r = iov_send_recv(sockfd, iov, iovcnt, offset, bytes, true);
  67  *
  68  * is logically equivalent to
  69  *
  70  *   char *buf = malloc(bytes);
  71  *   iov_to_buf(iov, iovcnt, offset, buf, bytes);
  72  *   r = send(sockfd, buf, bytes, 0);
  73  *   free(buf);
  74  *
  75  * For iov_send_recv() _whole_ area being sent or received
  76  * should be within the iovec, not only beginning of it.
  77  */
  78 ssize_t iov_send_recv(int sockfd, struct iovec *iov, unsigned iov_cnt,
  79                       size_t offset, size_t bytes, bool do_send);
  80 #define iov_recv(sockfd, iov, iov_cnt, offset, bytes) \
  81   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, false)
  82 #define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
  83   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
  84
  85 /**
  86  * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
  87  * in file `fp', prefixing each line with `prefix' and processing not more
  88  * than `limit' data bytes.
  89  */
  90 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
  91                  FILE *fp, const char *prefix, size_t limit);
  92
  93 /*
  94  * Partial copy of vector from iov to dst_iov (data is not copied).
  95  * dst_iov overlaps iov at a specified offset.
  96  * size of dst_iov is at most bytes. dst vector count is returned.
  97  */
  98 unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
  99                  const struct iovec *iov, unsigned int iov_cnt,
 100                  size_t offset, size_t bytes);
 101
 102 #endif