The iov_discard_front/back() operations are useful for parsing iovecs but they modify the array elements. If the original array is needed after parsing finishes there is currently no way to restore it. Although g_memdup() can be used before performing destructive iov_discard_front/back() operations, this is inefficient. Introduce iov_discard_undo() to restore the array to the state prior to an iov_discard_front/back() operation. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Li Qiang <liq3ea@gmail.com> Message-Id: <20200917094455.822379-2-stefanha@redhat.com>
253 lines
9.6 KiB
C
253 lines
9.6 KiB
C
/*
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* Helpers for using (partial) iovecs.
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*
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* Copyright (C) 2010 Red Hat, Inc.
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*
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* Author(s):
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* Amit Shah <amit.shah@redhat.com>
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* Michael Tokarev <mjt@tls.msk.ru>
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*
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* This work is licensed under the terms of the GNU GPL, version 2. See
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* the COPYING file in the top-level directory.
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*/
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#ifndef IOV_H
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#define IOV_H
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/**
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* count and return data size, in bytes, of an iovec
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* starting at `iov' of `iov_cnt' number of elements.
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*/
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size_t iov_size(const struct iovec *iov, const unsigned int iov_cnt);
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/**
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* Copy from single continuous buffer to scatter-gather vector of buffers
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* (iovec) and back like memcpy() between two continuous memory regions.
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* Data in single continuous buffer starting at address `buf' and
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* `bytes' bytes long will be copied to/from an iovec `iov' with
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* `iov_cnt' number of elements, starting at byte position `offset'
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* within the iovec. If the iovec does not contain enough space,
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* only part of data will be copied, up to the end of the iovec.
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* Number of bytes actually copied will be returned, which is
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* min(bytes, iov_size(iov)-offset)
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* `Offset' must point to the inside of iovec.
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*/
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size_t iov_from_buf_full(const struct iovec *iov, unsigned int iov_cnt,
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size_t offset, const void *buf, size_t bytes);
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size_t iov_to_buf_full(const struct iovec *iov, const unsigned int iov_cnt,
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size_t offset, void *buf, size_t bytes);
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static inline size_t
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iov_from_buf(const struct iovec *iov, unsigned int iov_cnt,
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size_t offset, const void *buf, size_t bytes)
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{
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if (__builtin_constant_p(bytes) && iov_cnt &&
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offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
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memcpy(iov[0].iov_base + offset, buf, bytes);
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return bytes;
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} else {
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return iov_from_buf_full(iov, iov_cnt, offset, buf, bytes);
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}
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}
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static inline size_t
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iov_to_buf(const struct iovec *iov, const unsigned int iov_cnt,
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size_t offset, void *buf, size_t bytes)
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{
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if (__builtin_constant_p(bytes) && iov_cnt &&
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offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
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memcpy(buf, iov[0].iov_base + offset, bytes);
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return bytes;
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} else {
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return iov_to_buf_full(iov, iov_cnt, offset, buf, bytes);
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}
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}
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/**
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* Set data bytes pointed out by iovec `iov' of size `iov_cnt' elements,
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* starting at byte offset `start', to value `fillc', repeating it
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* `bytes' number of times. `Offset' must point to the inside of iovec.
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* If `bytes' is large enough, only last bytes portion of iovec,
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* up to the end of it, will be filled with the specified value.
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* Function return actual number of bytes processed, which is
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* min(size, iov_size(iov) - offset).
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*/
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size_t iov_memset(const struct iovec *iov, const unsigned int iov_cnt,
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size_t offset, int fillc, size_t bytes);
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/*
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* Send/recv data from/to iovec buffers directly
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*
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* `offset' bytes in the beginning of iovec buffer are skipped and
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* next `bytes' bytes are used, which must be within data of iovec.
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*
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* r = iov_send_recv(sockfd, iov, iovcnt, offset, bytes, true);
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*
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* is logically equivalent to
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*
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* char *buf = malloc(bytes);
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* iov_to_buf(iov, iovcnt, offset, buf, bytes);
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* r = send(sockfd, buf, bytes, 0);
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* free(buf);
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*
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* For iov_send_recv() _whole_ area being sent or received
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* should be within the iovec, not only beginning of it.
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*/
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ssize_t iov_send_recv(int sockfd, const struct iovec *iov, unsigned iov_cnt,
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size_t offset, size_t bytes, bool do_send);
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#define iov_recv(sockfd, iov, iov_cnt, offset, bytes) \
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iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, false)
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#define iov_send(sockfd, iov, iov_cnt, offset, bytes) \
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iov_send_recv(sockfd, iov, iov_cnt, offset, bytes, true)
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/**
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* Produce a text hexdump of iovec `iov' with `iov_cnt' number of elements
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* in file `fp', prefixing each line with `prefix' and processing not more
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* than `limit' data bytes.
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*/
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void iov_hexdump(const struct iovec *iov, const unsigned int iov_cnt,
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FILE *fp, const char *prefix, size_t limit);
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/*
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* Partial copy of vector from iov to dst_iov (data is not copied).
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* dst_iov overlaps iov at a specified offset.
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* size of dst_iov is at most bytes. dst vector count is returned.
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*/
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unsigned iov_copy(struct iovec *dst_iov, unsigned int dst_iov_cnt,
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const struct iovec *iov, unsigned int iov_cnt,
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size_t offset, size_t bytes);
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/*
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* Remove a given number of bytes from the front or back of a vector.
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* This may update iov and/or iov_cnt to exclude iovec elements that are
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* no longer required.
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*
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* The number of bytes actually discarded is returned. This number may be
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* smaller than requested if the vector is too small.
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*/
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size_t iov_discard_front(struct iovec **iov, unsigned int *iov_cnt,
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size_t bytes);
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size_t iov_discard_back(struct iovec *iov, unsigned int *iov_cnt,
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size_t bytes);
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/* Information needed to undo an iov_discard_*() operation */
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typedef struct {
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struct iovec *modified_iov;
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struct iovec orig;
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} IOVDiscardUndo;
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/*
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* Undo an iov_discard_front_undoable() or iov_discard_back_undoable()
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* operation. If multiple operations are made then each one needs a separate
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* IOVDiscardUndo and iov_discard_undo() must be called in the reverse order
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* that the operations were made.
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*/
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void iov_discard_undo(IOVDiscardUndo *undo);
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/*
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* Undoable versions of iov_discard_front() and iov_discard_back(). Use
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* iov_discard_undo() to reset to the state before the discard operations.
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*/
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size_t iov_discard_front_undoable(struct iovec **iov, unsigned int *iov_cnt,
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size_t bytes, IOVDiscardUndo *undo);
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size_t iov_discard_back_undoable(struct iovec *iov, unsigned int *iov_cnt,
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size_t bytes, IOVDiscardUndo *undo);
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typedef struct QEMUIOVector {
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struct iovec *iov;
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int niov;
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/*
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* For external @iov (qemu_iovec_init_external()) or allocated @iov
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* (qemu_iovec_init()), @size is the cumulative size of iovecs and
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* @local_iov is invalid and unused.
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*
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* For embedded @iov (QEMU_IOVEC_INIT_BUF() or qemu_iovec_init_buf()),
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* @iov is equal to &@local_iov, and @size is valid, as it has same
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* offset and type as @local_iov.iov_len, which is guaranteed by
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* static assertion below.
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*
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* @nalloc is always valid and is -1 both for embedded and external
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* cases. It is included in the union only to ensure the padding prior
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* to the @size field will not result in a 0-length array.
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*/
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union {
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struct {
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int nalloc;
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struct iovec local_iov;
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};
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struct {
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char __pad[sizeof(int) + offsetof(struct iovec, iov_len)];
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size_t size;
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};
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};
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} QEMUIOVector;
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QEMU_BUILD_BUG_ON(offsetof(QEMUIOVector, size) !=
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offsetof(QEMUIOVector, local_iov.iov_len));
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#define QEMU_IOVEC_INIT_BUF(self, buf, len) \
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{ \
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.iov = &(self).local_iov, \
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.niov = 1, \
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.nalloc = -1, \
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.local_iov = { \
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.iov_base = (void *)(buf), /* cast away const */ \
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.iov_len = (len), \
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}, \
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}
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/*
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* qemu_iovec_init_buf
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*
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* Initialize embedded QEMUIOVector.
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*
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* Note: "const" is used over @buf pointer to make it simple to pass
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* const pointers, appearing in read functions. Then this "const" is
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* cast away by QEMU_IOVEC_INIT_BUF().
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*/
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static inline void qemu_iovec_init_buf(QEMUIOVector *qiov,
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const void *buf, size_t len)
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{
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*qiov = (QEMUIOVector) QEMU_IOVEC_INIT_BUF(*qiov, buf, len);
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}
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static inline void *qemu_iovec_buf(QEMUIOVector *qiov)
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{
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/* Only supports embedded iov */
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assert(qiov->nalloc == -1 && qiov->iov == &qiov->local_iov);
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return qiov->local_iov.iov_base;
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}
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void qemu_iovec_init(QEMUIOVector *qiov, int alloc_hint);
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void qemu_iovec_init_external(QEMUIOVector *qiov, struct iovec *iov, int niov);
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void qemu_iovec_init_extended(
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QEMUIOVector *qiov,
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void *head_buf, size_t head_len,
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QEMUIOVector *mid_qiov, size_t mid_offset, size_t mid_len,
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void *tail_buf, size_t tail_len);
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void qemu_iovec_init_slice(QEMUIOVector *qiov, QEMUIOVector *source,
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size_t offset, size_t len);
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int qemu_iovec_subvec_niov(QEMUIOVector *qiov, size_t offset, size_t len);
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void qemu_iovec_add(QEMUIOVector *qiov, void *base, size_t len);
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void qemu_iovec_concat(QEMUIOVector *dst,
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QEMUIOVector *src, size_t soffset, size_t sbytes);
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size_t qemu_iovec_concat_iov(QEMUIOVector *dst,
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struct iovec *src_iov, unsigned int src_cnt,
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size_t soffset, size_t sbytes);
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bool qemu_iovec_is_zero(QEMUIOVector *qiov, size_t qiov_offeset, size_t bytes);
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void qemu_iovec_destroy(QEMUIOVector *qiov);
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void qemu_iovec_reset(QEMUIOVector *qiov);
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size_t qemu_iovec_to_buf(QEMUIOVector *qiov, size_t offset,
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void *buf, size_t bytes);
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size_t qemu_iovec_from_buf(QEMUIOVector *qiov, size_t offset,
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const void *buf, size_t bytes);
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size_t qemu_iovec_memset(QEMUIOVector *qiov, size_t offset,
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int fillc, size_t bytes);
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ssize_t qemu_iovec_compare(QEMUIOVector *a, QEMUIOVector *b);
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void qemu_iovec_clone(QEMUIOVector *dest, const QEMUIOVector *src, void *buf);
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void qemu_iovec_discard_back(QEMUIOVector *qiov, size_t bytes);
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#endif
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