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 void qemu_iovec_init_slice(QEMUIOVector *qiov, QEMUIOVector *source, 226 size_t offset, size_t len); 227 struct iovec *qemu_iovec_slice(QEMUIOVector *qiov, 228 size_t offset, size_t len, 229 size_t *head, size_t *tail, int *niov); 230 int qemu_iovec_subvec_niov(QEMUIOVector *qiov, size_t offset, size_t len); 231 void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len); 232 void qemu_iovec_concat(QEMUIOVector *dst, 233 QEMUIOVector *src, size_t soffset, size_t sbytes); 234 size_t qemu_iovec_concat_iov(QEMUIOVector *dst, 235 struct iovec *src_iov, unsigned int src_cnt, 236 size_t soffset, size_t sbytes); 237 bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t qiov_offeset, size_t bytes); 238 void qemu_iovec_destroy(QEMUIOVector *qiov); 239 void qemu_iovec_reset(QEMUIOVector *qiov); 240 size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset, 241 void *buf, size_t bytes); 242 size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset, 243 const void *buf, size_t bytes); 244 size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset, 245 int fillc, size_t bytes); 246 ssize_t qemu_iovec_compare(QEMUIOVector *a, QEMUIOVector *b); 247 void qemu_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src, void *buf); 248 void qemu_iovec_discard_back(QEMUIOVector *qiov, size_t bytes); 249 250 #endif 251