tap_send_frames_passt() needs to determine which buffer element a byte
offset into an IO vector lies in. We have some upcoming uses for similar
logic, so split this out into a helper function iov_offset().
Signed-off-by: David Gibson <david(a)gibson.dropbear.id.au>
---
tap.c | 13 +++++--------
util.c | 23 +++++++++++++++++++++++
util.h | 1 +
3 files changed, 29 insertions(+), 8 deletions(-)
diff --git a/tap.c b/tap.c
index 396dee7e..f15eba6e 100644
--- a/tap.c
+++ b/tap.c
@@ -390,22 +390,19 @@ static size_t tap_send_frames_passt(const struct ctx *c,
.msg_iovlen = n,
};
unsigned int i;
+ size_t offset;
ssize_t sent;
sent = sendmsg(c->fd_tap, &mh, MSG_NOSIGNAL | MSG_DONTWAIT);
if (sent < 0)
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;
- }
+ offset = (size_t)sent;
+ i = iov_offset(iov, n, &offset);
- if (i < n && sent) {
+ if (i < n && offset) {
/* A partial frame was sent */
- tap_send_remainder(c, &iov[i], sent);
+ tap_send_remainder(c, &iov[i], offset);
i++;
}
diff --git a/util.c b/util.c
index 21b35ff9..fb6a0430 100644
--- a/util.c
+++ b/util.c
@@ -574,3 +574,26 @@ int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size,
int flags,
return clone(fn, stack_area + stack_size / 2, flags, arg);
#endif
}
+
+/* iov_offset() - interpret offset into an IO vector
+ * @iov: IO vector
+ * @n: Number of entries in @iov
+ * @offset: Pointer to offset into IO vector
+ *
+ * Return: index I of iovec which contains the given offset, or @n if
+ * the given offset is >= the total # of bytes in the vector.
+ * *@offset is updated to be the byte offset into (@iov + I),
+ * and is guaranteed to be less than @iov[I].iov_len
+ */
+size_t iov_offset(const struct iovec *iov, size_t n, size_t *offset)
+{
+ size_t i;
+
+ for (i = 0; i < n; i++) {
+ if (*offset < iov[i].iov_len)
+ break;
+ *offset -= iov[i].iov_len;
+ }
+
+ return i;
+}
diff --git a/util.h b/util.h
index d2320f8c..62fad6fe 100644
--- a/util.h
+++ b/util.h
@@ -229,6 +229,7 @@ void write_pidfile(int fd, pid_t pid);
int __daemon(int pidfile_fd, int devnull_fd);
int fls(unsigned long x);
int write_file(const char *path, const char *buf);
+size_t iov_offset(const struct iovec *iov, size_t n, size_t *offset);
/**
* mod_sub() - Modular arithmetic subtraction
--
2.43.2