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  */
  35 size_t iov_from_buf_full(const struct iovec *iov, unsigned int iov_cnt,
  36                          size_t offset, const void *buf, size_t bytes);
  37 size_t iov_to_buf_full(const struct iovec *iov, const unsigned int iov_cnt,
  38                        size_t offset, void *buf, size_t bytes);
  39
  40 static inline size_t
  41 iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
  42              size_t offset, const void *buf, size_t bytes)
  43 {
  44     if (__builtin_constant_p(bytes) && iov_cnt &&
  45         offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
  46         memcpy(iov[0].iov_base + offset, buf, bytes);
  47         return bytes;
  48     } else {
  49         return iov_from_buf_full(iov, iov_cnt, offset, buf, bytes);
  50     }
  51 }
  52
  53 static inline size_t
  54 iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
  55            size_t offset, void *buf, size_t bytes)
  56 {
  57     if (__builtin_constant_p(bytes) && iov_cnt &&
  58         offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
  59         memcpy(buf, iov[0].iov_base + offset, bytes);
  60         return bytes;
  61     } else {
  62         return iov_to_buf_full(iov, iov_cnt, offset, buf, bytes);
  63     }
  64 }
  65
  66 /**
  67  * Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
  68  * starting at byte offset `start', to value `fillc', repeating it
  69  * `bytes' number of times.  `Offset' must point to the inside of iovec.
  70  * If `bytes' is large enough, only last bytes portion of iovec,
  71  * up to the end of it, will be filled with the specified value.
  72  * Function return actual number of bytes processed, which is
  73  * min(size, iov_size(iov) - offset).
  74  */
  75 size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
  76                   size_t offset, int fillc, size_t bytes);
  77
  78 /*
  79  * Send/recv data from/to iovec buffers directly
  80  *
  81  * `offset' bytes in the beginning of iovec buffer are skipped and
  82  * next `bytes' bytes are used, which must be within data of iovec.
  83  *
  84  *   r = iov_send_recv(sockfd, iov, iovcnt, offset, bytes, true);
  85  *
  86  * is logically equivalent to
  87  *
  88  *   char *buf = malloc(bytes);
  89  *   iov_to_buf(iov, iovcnt, offset, buf, bytes);
  90  *   r = send(sockfd, buf, bytes, 0);
  91  *   free(buf);
  92  *
  93  * For iov_send_recv() _whole_ area being sent or received
  94  * should be within the iovec, not only beginning of it.
  95  */
  96 ssize_t iov_send_recv(int sockfd, const struct iovec *iov, unsigned iov_cnt,
  97                       size_t offset, size_t bytes, bool do_send);
  98 #define iov_recv(sockfd, iov, iov_cnt, offset, bytes) \
  99   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, false)
 100 #define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
 101   iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
 102
 103 /**
 104  * Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
 105  * in file `fp', prefixing each line with `prefix' and processing not more
 106  * than `limit' data bytes.
 107  */
 108 void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
 109                  FILE *fp, const char *prefix, size_t limit);
 110
 111 /*
 112  * Partial copy of vector from iov to dst_iov (data is not copied).
 113  * dst_iov overlaps iov at a specified offset.
 114  * size of dst_iov is at most bytes. dst vector count is returned.
 115  */
 116 unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
 117                  const struct iovec *iov, unsigned int iov_cnt,
 118                  size_t offset, size_t bytes);
 119
 120 /*
 121  * Remove a given number of bytes from the front or back of a vector.
 122  * This may update iov and/or iov_cnt to exclude iovec elements that are
 123  * no longer required.
 124  *
 125  * The number of bytes actually discarded is returned.  This number may be
 126  * smaller than requested if the vector is too small.
 127  */
 128 size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
 129                          size_t bytes);
 130 size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
 131                         size_t bytes);
 132
 133 /* Information needed to undo an iov_discard_*() operation */
 134 typedef struct {
 135     struct iovec *modified_iov;
 136     struct iovec orig;
 137 } IOVDiscardUndo;
 138
 139 /*
 140  * Undo an iov_discard_front_undoable() or iov_discard_back_undoable()
 141  * operation. If multiple operations are made then each one needs a separate
 142  * IOVDiscardUndo and iov_discard_undo() must be called in the reverse order
 143  * that the operations were made.
 144  */
 145 void iov_discard_undo(IOVDiscardUndo *undo);
 146
 147 /*
 148  * Undoable versions of iov_discard_front() and iov_discard_back(). Use
 149  * iov_discard_undo() to reset to the state before the discard operations.
 150  */
 151 size_t iov_discard_front_undoable(struct iovec **iov, unsigned int *iov_cnt,
 152                                   size_t bytes, IOVDiscardUndo *undo);
 153 size_t iov_discard_back_undoable(struct iovec *iov, unsigned int *iov_cnt,
 154                                  size_t bytes, IOVDiscardUndo *undo);
 155
 156 typedef struct QEMUIOVector {
 157     struct iovec *iov;
 158     int niov;
 159
 160     /*
 161      * For external @iov (qemu_iovec_init_external()) or allocated @iov
 162      * (qemu_iovec_init()), @size is the cumulative size of iovecs and
 163      * @local_iov is invalid and unused.
 164      *
 165      * For embedded @iov (QEMU_IOVEC_INIT_BUF() or qemu_iovec_init_buf()),
 166      * @iov is equal to &@local_iov, and @size is valid, as it has same
 167      * offset and type as @local_iov.iov_len, which is guaranteed by
 168      * static assertion below.
 169      *
 170      * @nalloc is always valid and is -1 both for embedded and external
 171      * cases. It is included in the union only to ensure the padding prior
 172      * to the @size field will not result in a 0-length array.
 173      */
 174     union {
 175         struct {
 176             int nalloc;
 177             struct iovec local_iov;
 178         };
 179         struct {
 180             char __pad[sizeof(int) + offsetof(struct iovec, iov_len)];
 181             size_t size;
 182         };
 183     };
 184 } QEMUIOVector;
 185
 186 QEMU_BUILD_BUG_ON(offsetof(QEMUIOVector, size) !=
 187                   offsetof(QEMUIOVector, local_iov.iov_len));
 188
 189 #define QEMU_IOVEC_INIT_BUF(self, buf, len)              \
 190 {                                                        \
 191     .iov = &(self).local_iov,                            \
 192     .niov = 1,                                           \
 193     .nalloc = -1,                                        \
 194     .local_iov = {                                       \
 195         .iov_base = (void *)(buf), /* cast away const */ \
 196         .iov_len = (len),                                \
 197     },                                                   \
 198 }
 199
 200 /*
 201  * qemu_iovec_init_buf
 202  *
 203  * Initialize embedded QEMUIOVector.
 204  *
 205  * Note: "const" is used over @buf pointer to make it simple to pass
 206  * const pointers, appearing in read functions. Then this "const" is
 207  * cast away by QEMU_IOVEC_INIT_BUF().
 208  */
 209 static inline void qemu_iovec_init_buf(QEMUIOVector *qiov,
 210                                        const void *buf, size_t len)
 211 {
 212     *qiov = (QEMUIOVector) QEMU_IOVEC_INIT_BUF(*qiov, buf, len);
 213 }
 214
 215 static inline void *qemu_iovec_buf(QEMUIOVector *qiov)
 216 {
 217     /* Only supports embedded iov */
 218     assert(qiov->nalloc == -1 && qiov->iov == &qiov->local_iov);
 219
 220     return qiov->local_iov.iov_base;
 221 }
 222
 223 void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
 224 void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
 225 int qemu_iovec_init_extended(
 226         QEMUIOVector *qiov,
 227         void *head_buf, size_t head_len,
 228         QEMUIOVector *mid_qiov, size_t mid_offset, size_t mid_len,
 229         void *tail_buf, size_t tail_len);
 230 void qemu_iovec_init_slice(QEMUIOVector *qiov, QEMUIOVector *source,
 231                            size_t offset, size_t len);
 232 int qemu_iovec_subvec_niov(QEMUIOVector *qiov, size_t offset, size_t len);
 233 void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
 234 void qemu_iovec_concat(QEMUIOVector *dst,
 235                        QEMUIOVector *src, size_t soffset, size_t sbytes);
 236 size_t qemu_iovec_concat_iov(QEMUIOVector *dst,
 237                              struct iovec *src_iov, unsigned int src_cnt,
 238                              size_t soffset, size_t sbytes);
 239 bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t qiov_offeset, size_t bytes);
 240 void qemu_iovec_destroy(QEMUIOVector *qiov);
 241 void qemu_iovec_reset(QEMUIOVector *qiov);
 242 size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
 243                          void *buf, size_t bytes);
 244 size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
 245                            const void *buf, size_t bytes);
 246 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
 247                          int fillc, size_t bytes);
 248 ssize_t qemu_iovec_compare(QEMUIOVector *a, QEMUIOVector *b);
 249 void qemu_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src, void *buf);
 250 void qemu_iovec_discard_back(QEMUIOVector *qiov, size_t bytes);
 251
 252 #endif