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| | // SPDX-License-Identifier: GPL-2.0-or-later
/*
* iov.h - helpers for using (partial) iovecs.
*
* Copyright Red Hat
* Author: Laurent Vivier <lvivier@redhat.com>
*
* This file also contains code originally from QEMU include/qemu/iov.h
* and licensed under the following terms:
*
* Copyright (C) 2010 Red Hat, Inc.
*
* Author(s):
* Amit Shah <amit.shah@redhat.com>
* Michael Tokarev <mjt@tls.msk.ru>
*
* This work is licensed under the terms of the GNU GPL, version 2. See
* the COPYING file in the top-level directory.
*
* Contributions after 2012-01-13 are licensed under the terms of the
* GNU GPL, version 2 or (at your option) any later version.
*/
#include <sys/socket.h>
#include "util.h"
#include "iov.h"
/* iov_skip_bytes() - Skip leading bytes of an IO vector
* @iov: IO vector
* @n: Number of entries in @iov
* @skip: Number of leading bytes of @iov to skip
* @offset: Offset of first unskipped byte in its @iov entry
*
* Return: index I of individual struct iovec which contains the byte at @skip
* bytes into the vector (as though all its buffers were contiguous).
* If @offset is non-NULL, update it to the offset of that byte within
* @iov[I] (guaranteed to be less than @iov[I].iov_len) If the whole
* vector has <= @skip bytes, return @n.
*/
size_t iov_skip_bytes(const struct iovec *iov, size_t n,
size_t skip, size_t *offset)
{
size_t off = skip, i;
for (i = 0; i < n; i++) {
if (off < iov[i].iov_len)
break;
off -= iov[i].iov_len;
}
if (offset)
*offset = off;
return i;
}
/**
* iov_from_buf - Copy data from a buffer to an I/O vector (struct iovec)
* efficiently.
*
* @iov: Pointer to the array of struct iovec describing the
* scatter/gather I/O vector.
* @iov_cnt: Number of elements in the iov array.
* @offset: Byte offset in the iov array where copying should start.
* @buf: Pointer to the source buffer containing the data to copy.
* @bytes: Total number of bytes to copy from buf to iov.
*
* Returns: The number of bytes successfully copied.
*/
size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
size_t offset, const void *buf, size_t bytes)
{
unsigned int i;
size_t copied;
if (__builtin_constant_p(bytes) && iov_cnt &&
offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
memcpy((char *)iov[0].iov_base + offset, buf, bytes);
return bytes;
}
i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
/* copying data */
for (copied = 0; copied < bytes && i < iov_cnt; i++) {
size_t len = MIN(iov[i].iov_len - offset, bytes - copied);
memcpy((char *)iov[i].iov_base + offset, (char *)buf + copied,
len);
copied += len;
offset = 0;
}
return copied;
}
/**
* iov_to_buf - Copy data from a scatter/gather I/O vector (struct iovec) to
* a buffer efficiently.
*
* @iov: Pointer to the array of struct iovec describing the scatter/gather
* I/O vector.
* @iov_cnt: Number of elements in the iov array.
* @offset: Offset within the first element of iov from where copying should start.
* @buf: Pointer to the destination buffer where data will be copied.
* @bytes: Total number of bytes to copy from iov to buf.
*
* Returns: The number of bytes successfully copied.
*/
/* cppcheck-suppress unusedFunction */
size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,
size_t offset, void *buf, size_t bytes)
{
unsigned int i;
size_t copied;
if (__builtin_constant_p(bytes) && iov_cnt &&
offset <= iov[0].iov_len && bytes <= iov[0].iov_len - offset) {
memcpy(buf, (char *)iov[0].iov_base + offset, bytes);
return bytes;
}
i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
/* copying data */
for (copied = 0; copied < bytes && i < iov_cnt; i++) {
size_t len = MIN(iov[i].iov_len - offset, bytes - copied);
memcpy((char *)buf + copied, (char *)iov[i].iov_base + offset,
len);
copied += len;
offset = 0;
}
return copied;
}
/**
* iov_size - Calculate the total size of a scatter/gather I/O vector
* (struct iovec).
*
* @iov: Pointer to the array of struct iovec describing the
* scatter/gather I/O vector.
* @iov_cnt: Number of elements in the iov array.
*
* Returns: The total size in bytes.
*/
size_t iov_size(const struct iovec *iov, size_t iov_cnt)
{
unsigned int i;
size_t len;
for (i = 0, len = 0; i < iov_cnt; i++)
len += iov[i].iov_len;
return len;
}
/**
* iov_count - Calculate the number of I/O vectors and the size of
* the last one to store a given number of bytes.
*
* @iov: Pointer to the array of struct iovec describing the
* scatter/gather I/O vector.
* @iov_cnt: Number of elements in the iov array.
* @size: number of bytes we need to store in iovec
* @last_iov_length: output parameter, length used in the last iovec
* if return value is 0, this output parameter is
* undefined.
*
* Returns: The number of iovec needed to store @size bytes.
*/
size_t iov_count(const struct iovec *iov, size_t iov_cnt,
size_t size, size_t *last_iov_length)
{
size_t n = 0;
while (size && n < iov_cnt) {
if (size <= iov[n].iov_len) {
*last_iov_length = size;
return n + 1;
}
size -= iov[n].iov_len;
n++;
}
if (n > 0)
*last_iov_length = iov[n - 1].iov_len;
return n;
}
|