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From: David Gibson <david@gibson.dropbear.id.au>
To: passt-dev@passt.top, Stefano Brivio <sbrivio@redhat.com>,
	Laurent Vivier <lvivier@redhat.com>
Cc: David Gibson <david@gibson.dropbear.id.au>
Subject: [PATCH 1/6] util: Add helper to find offset into io vector
Date: Thu, 22 Feb 2024 16:55:57 +1100	[thread overview]
Message-ID: <20240222055602.1872516-2-david@gibson.dropbear.id.au> (raw)
In-Reply-To: <20240222055602.1872516-1-david@gibson.dropbear.id.au>

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@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
-- 
@@ -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


  reply	other threads:[~2024-02-22  5:56 UTC|newest]

Thread overview: 16+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-02-22  5:55 [PATCH 0/6] Allow more use of iovecs in pcap and tap interfaces David Gibson
2024-02-22  5:55 ` David Gibson [this message]
2024-02-27 14:23   ` [PATCH 1/6] util: Add helper to find offset into io vector Stefano Brivio
2024-02-27 23:27     ` David Gibson
2024-02-22  5:55 ` [PATCH 2/6] pcap: Update pcap_frame() to take an iovec and offset David Gibson
2024-02-27 14:23   ` Stefano Brivio
2024-02-22  5:55 ` [PATCH 3/6] util: Add write_remainder() helper David Gibson
2024-02-27 14:25   ` Stefano Brivio
2024-02-28  0:44     ` David Gibson
2024-02-28  6:24       ` Stefano Brivio
2024-02-28  9:04         ` David Gibson
2024-02-28  9:22           ` Stefano Brivio
2024-02-22  5:56 ` [PATCH 4/6] pcap: Handle short writes in pcap_frame() David Gibson
2024-02-22  5:56 ` [PATCH 5/6] pcap: Allow pcap_frame() and pcap_multiple() to take multi-buffer frames David Gibson
2024-02-27 14:26   ` Stefano Brivio
2024-02-22  5:56 ` [PATCH 6/6] tap: Use write_remainder() in tap_send_frames_passt() David Gibson

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