xref: /openbmc/qemu/include/qemu/iov.h (revision cc63f6f6)
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
iov_from_buf(const struct iovec * iov,unsigned int iov_cnt,size_t offset,const void * buf,size_t bytes)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
iov_to_buf(const struct iovec * iov,const unsigned int iov_cnt,size_t offset,void * buf,size_t bytes)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  */
qemu_iovec_init_buf(QEMUIOVector * qiov,const void * buf,size_t len)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 
qemu_iovec_buf(QEMUIOVector * qiov)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