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iov: Add helper to find skip over first n bytes of an io vector

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Several of the IOV functions in iov.c, and also tap_send_frames_passt()
needs to determine which buffer element a byte offset into an IO vector
lies in.  Split this out into a helper function iov_skip_bytes().

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
This commit is contained in:
David Gibson 2024-02-28 12:52:01 +11:00 committed by Stefano Brivio
parent 2a6f8bcca7
commit 64b63d9e3e
3 changed files with 40 additions and 16 deletions
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42
iov.c
View file

@ -25,6 +25,36 @@
#include "util.h"
#include "iov.h"
/* iov_skip_bytes() - Skip the first n bytes into an IO vector
* @iov: IO vector
* @n: Number of entries in @iov
* @vec_offset: Total byte offset into the IO vector
* @buf_offset: Offset into a single buffer of the IO vector
*
* Return: index I of individual struct iovec which contains the byte at
* @vec_offset bytes into the vector (as though all its buffers were
* contiguous). If @buf_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 <= @vec_offset bytes, return @n.
*/
size_t iov_skip_bytes(const struct iovec *iov, size_t n,
size_t vec_offset, size_t *buf_offset)
{
size_t offset = vec_offset, i;
for (i = 0; i < n; i++) {
if (offset < iov[i].iov_len)
break;
offset -= iov[i].iov_len;
}
if (buf_offset)
*buf_offset = offset;
return i;
}
/**
* iov_from_buf - Copy data from a buffer to an I/O vector (struct iovec)
* efficiently.
@ -51,9 +81,7 @@ size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
return bytes;
}
/* skipping offset bytes in the iovec */
for (i = 0; i < iov_cnt && offset >= iov[i].iov_len; i++)
offset -= iov[i].iov_len;
i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
/* copying data */
for (copied = 0; copied < bytes && i < iov_cnt; i++) {
@ -94,9 +122,7 @@ size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,
return bytes;
}
/* skipping offset bytes in the iovec */
for (i = 0; i < iov_cnt && offset >= iov[i].iov_len; i++)
offset -= iov[i].iov_len;
i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
/* copying data */
for (copied = 0; copied < bytes && i < iov_cnt; i++) {
@ -155,9 +181,7 @@ unsigned iov_copy(struct iovec *dst_iov, size_t dst_iov_cnt,
{
unsigned int i, j;
/* skipping offset bytes in the iovec */
for (i = 0; i < iov_cnt && offset >= iov[i].iov_len; i++)
offset -= iov[i].iov_len;
i = iov_skip_bytes(iov, iov_cnt, offset, &offset);
/* copying data */
for (j = 0; i < iov_cnt && j < dst_iov_cnt && bytes; i++) {

2
iov.h
View file

@ -18,6 +18,8 @@
#include <unistd.h>
#include <string.h>
size_t iov_skip_bytes(const struct iovec *iov, size_t n,
size_t vec_offset, size_t *buf_offset);
size_t iov_from_buf(const struct iovec *iov, size_t iov_cnt,
size_t offset, const void *buf, size_t bytes);
size_t iov_to_buf(const struct iovec *iov, size_t iov_cnt,

12
tap.c
View file

@ -45,6 +45,7 @@
#include "checksum.h"
#include "util.h"
#include "iov.h"
#include "passt.h"
#include "arp.h"
#include "dhcp.h"
@ -389,6 +390,7 @@ static size_t tap_send_frames_passt(const struct ctx *c,
.msg_iov = (void *)iov,
.msg_iovlen = n,
};
size_t buf_offset;
unsigned int i;
ssize_t sent;
@ -397,15 +399,11 @@ static size_t tap_send_frames_passt(const struct ctx *c,
return 0;
/* Check for any partial frames due to short send */
for (i = 0; i < n; i++) {
if ((size_t)sent < iov[i].iov_len)
break;
sent -= iov[i].iov_len;
}
i = iov_skip_bytes(iov, n, sent, &buf_offset);
if (i < n && sent) {
if (i < n && buf_offset) {
/* A partial frame was sent */
tap_send_remainder(c, &iov[i], sent);
tap_send_remainder(c, &iov[i], buf_offset);
i++;
}