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(a)gibson.dropbear.id.au>
---
iov.c | 42 +++++++++++++++++++++++++++++++++---------
iov.h | 2 ++
tap.c | 12 +++++-------
3 files changed, 40 insertions(+), 16 deletions(-)
diff --git a/iov.c b/iov.c
index 8a48acb1..e3312628 100644
--- a/iov.c
+++ b/iov.c
@@ -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++) {
diff --git a/iov.h b/iov.h
index ee35a75d..e1becdea 100644
--- a/iov.h
+++ b/iov.h
@@ -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,
diff --git a/tap.c b/tap.c
index 396dee7e..dd11d1d4 100644
--- a/tap.c
+++ b/tap.c
@@ -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++;
}
--
2.43.2