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 /**
  18  * count and return data size, in bytes, of an iovec
  19  * starting at `iov' of `iov_cnt' number of elements.
  20  */
  21 size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
  22
  23 /**
  24  * Copy from single continuous buffer to scatter-gather vector of buffers
  25  * (iovec) and back like memcpy() between two continuous memory regions.
  26  * Data in single continuous buffer starting at address `buf' and
  27  * `bytes' bytes long will be copied to/from an iovec `iov' with
  28  * `iov_cnt' number of elements, starting at byte position `offset'
  29  * within the iovec.  If the iovec does not contain enough space,
  30  * only part of data will be copied, up to the end of the iovec.
  31  * Number of bytes actually copied will be returned, which is
  32  *  min(bytes, iov_size(iov)-offset)
  33  * `Offset' must point to the inside of iovec.
  34  * It is okay to use very large value for `bytes' since we're
  35  * limited by the size of the iovec anyway, provided that the
  36  * buffer pointed to by buf has enough space.  One possible
  37  * such "large" value is -1 (sinice size_t is unsigned),
  38  * so specifying `-1' as `bytes' means 'up to the end of iovec'.
  39  */
  40 size_t iov_from_buf_full(const struct iovec *iov, unsigned int iov_cnt,
  41                          size_t offset, const void *buf, size_t bytes);
  42 size_t iov_to_buf_full(const struct iovec *iov, const unsigned int iov_cnt,
  43                        size_t offset, void *buf, size_t bytes);
  44
  45 static inline size_t
  46 iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
  47              size_t offset, const void *buf, size_t bytes)
  48 {
  49     if (__builtin_constant_p(bytes) && iov_cnt &&
  50         offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
  51         memcpy(iov[0].iov_base + offset, buf, bytes);
  52         return bytes;
  53     } else {
  54         return iov_from_buf_full(iov, iov_cnt, offset, buf, bytes);
  55     }
  56 }
  57
  58 static inline size_t
  59 iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
  60            size_t offset, void *buf, size_t bytes)
  61 {
  62     if (__builtin_constant_p(bytes) && iov_cnt &&
  63         offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
  64         memcpy(buf, iov[0].iov_base + offset, bytes);
  65         return bytes;
  66     } else {
  67         return iov_to_buf_full(iov, iov_cnt, offset, buf, bytes);
  68     }
  69 }
  70
  71 /**
  72  * Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
  73  * starting at byte offset `start', to value `fillc', repeating it
  74  * `bytes' number of times.  `Offset' must point to the inside of iovec.
  75  * If `bytes' is large enough, only last bytes portion of iovec,
  76  * up to the end of it, will be filled with the specified value.
  77  * Function return actual number of bytes processed, which is
  78  * min(size, iov_size(iov) - offset).
  79  * Again, it is okay to use large value for `bytes' to mean "up to the end".
  80  */
  81 size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
  82                   size_t offset, int fillc, size_t bytes);
  83
  84 /*
  85  * Send/recv data from/to iovec buffers directly
  86  *
  87  * `offset' bytes in the beginning of iovec buffer are skipped and
  88  * next `bytes' bytes are used, which must be within data of iovec.
  89  *
  90  *   r = iov_send_recv(sockfd, iov, iovcnt, offset, bytes, true);
  91  *
  92  * is logically equivalent to
  93  *
  94  *   char *buf = malloc(bytes);
  95  *   iov_to_buf(iov, iovcnt, offset, buf, bytes);
  96  *   r = send(sockfd, buf, bytes, 0);
  97  *   free(buf);
  98  *
  99  * For iov_send_recv() _whole_ area being sent or received
 100  * should be within the iovec, not only beginning of it.
 101  */
 102 ssize_t iov_send_recv(int sockfd, const struct iovec *iov, unsigned iov_cnt,
 103                       size_t offset, size_t bytes, bool do_send);
 104 #define iov_recv(sockfd, iov, iov_cnt, offset, bytes) \
 105   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, false)
 106 #define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
 107   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
 108
 109 /**
 110  * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
 111  * in file `fp', prefixing each line with `prefix' and processing not more
 112  * than `limit' data bytes.
 113  */
 114 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
 115                  FILE *fp, const char *prefix, size_t limit);
 116
 117 /*
 118  * Partial copy of vector from iov to dst_iov (data is not copied).
 119  * dst_iov overlaps iov at a specified offset.
 120  * size of dst_iov is at most bytes. dst vector count is returned.
 121  */
 122 unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
 123                  const struct iovec *iov, unsigned int iov_cnt,
 124                  size_t offset, size_t bytes);
 125
 126 /*
 127  * Remove a given number of bytes from the front or back of a vector.
 128  * This may update iov and/or iov_cnt to exclude iovec elements that are
 129  * no longer required.
 130  *
 131  * The number of bytes actually discarded is returned.  This number may be
 132  * smaller than requested if the vector is too small.
 133  */
 134 size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
 135                          size_t bytes);
 136 size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
 137                         size_t bytes);
 138
 139 typedef struct QEMUIOVector {
 140     struct iovec *iov;
 141     int niov;
 142     int nalloc;
 143     size_t size;
 144 } QEMUIOVector;
 145
 146 void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
 147 void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
 148 void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
 149 void qemu_iovec_concat(QEMUIOVector *dst,
 150                        QEMUIOVector *src, size_t soffset, size_t sbytes);
 151 size_t qemu_iovec_concat_iov(QEMUIOVector *dst,
 152                              struct iovec *src_iov, unsigned int src_cnt,
 153                              size_t soffset, size_t sbytes);
 154 bool qemu_iovec_is_zero(QEMUIOVector *qiov);
 155 void qemu_iovec_destroy(QEMUIOVector *qiov);
 156 void qemu_iovec_reset(QEMUIOVector *qiov);
 157 size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
 158                          void *buf, size_t bytes);
 159 size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
 160                            const void *buf, size_t bytes);
 161 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
 162                          int fillc, size_t bytes);
 163 ssize_t qemu_iovec_compare(QEMUIOVector *a, QEMUIOVector *b);
 164 void qemu_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src, void *buf);
 165 void qemu_iovec_discard_back(QEMUIOVector *qiov, size_t bytes);
 166
 167 #endif