[{"id":3674915,"web_url":"http://patchwork.ozlabs.org/comment/3674915/","msgid":"","list_archive_url":null,"date":"2026-04-08T12:13:19","subject":"Re: [RFC v4 5/5] chardev/socket: add AF_PACKET capture path","submitter":{"id":2694,"url":"http://patchwork.ozlabs.org/api/people/2694/","name":"Daniel P. Berrangé","email":"berrange@redhat.com"},"content":"On Tue, Apr 07, 2026 at 01:05:52PM +0800, Cindy Lu wrote:\n> Add the AF_PACKET capture read path for socket chardevs. When opened\n> with af-packet-mode=capture, the read side drains raw frames with\n> recvfrom(), keeps only PACKET_OUTGOING traffic, and feeds the result\n> through the normal chardev frontend interface.\n> \n> Signed-off-by: Cindy Lu \n> ---\n> chardev/char-socket.c | 133 +++++++++++++++++++++++++++++++++++++++++-\n> 1 file changed, 131 insertions(+), 2 deletions(-)\n> \n> diff --git a/chardev/char-socket.c b/chardev/char-socket.c\n> index 45d06fda8f..76a51a853d 100644\n> --- a/chardev/char-socket.c\n> +++ b/chardev/char-socket.c\n> @@ -107,9 +107,17 @@ static void tcp_chr_accept(QIONetListener *listener,\n> \n> static int tcp_chr_read_poll(void *opaque);\n> static void tcp_chr_disconnect_locked(Chardev *chr);\n> +static void tcp_chr_deliver_af_packet(Chardev *chr);\n> \n> #define TCP_CHARDEV_AF_PACKET_MAX_FRAME_SIZE 65536\n> \n> +static bool\n> +tcp_chr_uses_af_packet_capture(SocketChardev *s)\n> +{\n> + return s->is_af_packet && s->af_packet_mode_set &&\n> + s->af_packet_mode == CHARDEV_SOCKET_AF_PACKET_MODE_CAPTURE;\n> +}\n> +\n> static bool tcp_chr_uses_af_packet_inject(SocketChardev *s)\n> {\n> return s->is_af_packet &&\n> @@ -300,6 +308,9 @@ static int tcp_chr_read_poll(void *opaque)\n> return 0;\n> }\n> s->max_size = qemu_chr_be_can_write(chr);\n> + if (tcp_chr_uses_af_packet_capture(s) && s->af_packet_buf_len) {\n> + tcp_chr_deliver_af_packet(chr);\n> + }\n> return s->max_size;\n> }\n> \n> @@ -500,6 +511,98 @@ static void tcp_chr_reset_af_packet_send(SocketChardev *s)\n> s->af_packet_send_len_bytes = 0;\n> }\n> \n> +/* Push buffered AF_PACKET capture data into the chardev frontend. */\n> +static void\n> +tcp_chr_deliver_af_packet(Chardev *chr)\n> +{\n> + SocketChardev *s = SOCKET_CHARDEV(chr);\n> +\n> + while (s->max_size > 0 && s->af_packet_buf_offset < s->af_packet_buf_len) {\n> + size_t remaining = s->af_packet_buf_len - s->af_packet_buf_offset;\n> + size_t chunk = MIN((size_t)s->max_size, remaining);\n> +\n> + qemu_chr_be_write(chr, s->af_packet_buf + s->af_packet_buf_offset,\n> + (int)chunk);\n> + s->af_packet_buf_offset += chunk;\n> + s->max_size = qemu_chr_be_can_write(chr);\n> + }\n> +\n> + if (s->af_packet_buf_offset == s->af_packet_buf_len) {\n> + tcp_chr_reset_af_packet_buf(s);\n> + }\n> +}\n> +\n> +/* Copy buffered AF_PACKET capture data into a synchronous read buffer. */\n> +static int tcp_chr_copy_af_packet_buf(SocketChardev *s, uint8_t *buf,\n> + int len) {\n> + size_t remaining = s->af_packet_buf_len - s->af_packet_buf_offset;\n> + size_t copied = MIN((size_t)len, remaining);\n> +\n> + memcpy(buf, s->af_packet_buf + s->af_packet_buf_offset, copied);\n> + s->af_packet_buf_offset += copied;\n> +\n> + if (s->af_packet_buf_offset == s->af_packet_buf_len) {\n> + tcp_chr_reset_af_packet_buf(s);\n> + }\n> +\n> + return (int)copied;\n> +}\n> +\n> +static ssize_t\n> +tcp_chr_capture_af_packet(Chardev *chr)\n> +{\n> +#ifdef CONFIG_LINUX\n> + SocketChardev *s = SOCKET_CHARDEV(chr);\n> + struct sockaddr_ll sll;\n> + socklen_t sll_len;\n> + ssize_t size;\n> + uint32_t len;\n> +\n> + if (!tcp_chr_uses_af_packet_capture(s)) {\n> + errno = EIO;\n> + return -1;\n> + }\n> +\n> + if (s->af_packet_buf_size <\n> + sizeof(len) + TCP_CHARDEV_AF_PACKET_MAX_FRAME_SIZE) {\n> + s->af_packet_buf =\n> + g_realloc(s->af_packet_buf,\n> + sizeof(len) + TCP_CHARDEV_AF_PACKET_MAX_FRAME_SIZE);\n> + s->af_packet_buf_size =\n> + sizeof(len) + TCP_CHARDEV_AF_PACKET_MAX_FRAME_SIZE;\n> + }\n> +\n> + for (;;) {\n> + sll_len = sizeof(sll);\n> + do {\n> + size = recvfrom(s->sioc->fd, s->af_packet_buf + sizeof(len),\n> + TCP_CHARDEV_AF_PACKET_MAX_FRAME_SIZE, 0,\n> + (struct sockaddr *)&sll, &sll_len);\n> + } while (size < 0 && errno == EINTR);\n> +\n> + if (size <= 0) {\n> + if (size < 0 && errno != EAGAIN && errno != EWOULDBLOCK) {\n> + trace_chr_socket_recv_err(chr, chr->label, g_strerror(errno));\n> + }\n> + return size;\n> + }\n> +\n> + if (sll.sll_pkttype != PACKET_OUTGOING) {\n> + continue;\n> + }\n> +\n> + len = htonl(size);\n> + memcpy(s->af_packet_buf, &len, sizeof(len));\n> + s->af_packet_buf_len = sizeof(len) + size;\n> + s->af_packet_buf_offset = 0;\n> + return (ssize_t)s->af_packet_buf_len;\n> + }\n> +#else\n> + errno = EPROTONOSUPPORT;\n> + return -1;\n> +#endif\n> +}\n> +\n> static GSource *tcp_chr_add_watch(Chardev *chr, GIOCondition cond)\n> {\n> SocketChardev *s = SOCKET_CHARDEV(chr);\n> @@ -682,6 +785,22 @@ static gboolean tcp_chr_read(QIOChannel *chan, GIOCondition cond, void *opaque)\n> if (len > s->max_size) {\n> len = s->max_size;\n> }\n> + if (tcp_chr_uses_af_packet_capture(s)) {\n> + tcp_chr_deliver_af_packet(chr);\n> + if (s->max_size <= 0 || s->af_packet_buf_len) {\n> + return TRUE;\n> + }\n> +\n> + size = tcp_chr_capture_af_packet(chr);\n> + if (size == 0 || (size == -1 && errno != EAGAIN)) {\n> + tcp_chr_disconnect(chr);\n> + } else if (size > 0) {\n> + tcp_chr_deliver_af_packet(chr);\n> + }\n> +\n> + return TRUE;\n> + }\n> +\n> size = tcp_chr_recv(chr, (void *)buf, len);\n> if (size == 0 || (size == -1 && errno != EAGAIN)) {\n> /* connection closed */\n> @@ -715,6 +834,10 @@ static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)\n> int saved_errno;\n> Error *local_err = NULL;\n> \n> + if (tcp_chr_uses_af_packet_capture(s) && s->af_packet_buf_len) {\n> + return tcp_chr_copy_af_packet_buf(s, (uint8_t *)buf, len);\n> + }\n> +\n> if (s->state != TCP_CHARDEV_STATE_CONNECTED) {\n> return 0;\n> }\n> @@ -723,7 +846,14 @@ static int tcp_chr_sync_read(Chardev *chr, const uint8_t *buf, int len)\n> error_report_err(local_err);\n> return -1;\n> }\n> - size = tcp_chr_recv(chr, (void *) buf, len);\n> + if (tcp_chr_uses_af_packet_capture(s)) {\n> + size = tcp_chr_capture_af_packet(chr);\n> + if (size > 0) {\n> + size = tcp_chr_copy_af_packet_buf(s, (uint8_t *)buf, len);\n> + }\n> + } else {\n> + size = tcp_chr_recv(chr, (void *)buf, len);\n> + }\n\n\nSimilarly to the send side, I don't really think we should have this\npacket re-assembly logic in the chardev code. We should just be\ncalling the normal qio_channel_read APIs and let the netfilter code\nre-assemble packets it gets from the chardev. Mostly it seems we\nwould use TCP_CHARDEV_AF_PACKET_MAX_FRAME_SIZE instead of CHR_READ_BUF_LEN\nin the existing code paths.\n\n> saved_errno = errno;\n> if (s->state != TCP_CHARDEV_STATE_DISCONNECTED) {\n> if (!qio_channel_set_blocking(s->ioc, false, &local_err)) {\n> @@ -1448,7 +1578,6 @@ static gboolean socket_reconnect_timeout(gpointer opaque)\n> return false;\n> }\n> \n> -\n> static int qmp_chardev_open_socket_server(Chardev *chr,\n> bool is_telnet,\n> bool is_waitconnect,\n> -- \n> 2.52.0\n> \n> \n\nWith regards,\nDaniel","headers":{"Return-Path":"","X-Original-To":"incoming@patchwork.ozlabs.org","Delivered-To":"patchwork-incoming@legolas.ozlabs.org","Authentication-Results":["legolas.ozlabs.org;\n\tdkim=pass (1024-bit key;\n unprotected) header.d=redhat.com header.i=@redhat.com header.a=rsa-sha256\n header.s=mimecast20190719 header.b=dzDcA6ZP;\n\tdkim-atps=neutral","legolas.ozlabs.org;\n spf=pass (sender SPF authorized) smtp.mailfrom=nongnu.org\n (client-ip=209.51.188.17; helo=lists.gnu.org;\n envelope-from=qemu-devel-bounces+incoming=patchwork.ozlabs.org@nongnu.org;\n receiver=patchwork.ozlabs.org)"],"Received":["from lists.gnu.org (lists1p.gnu.org [209.51.188.17])\n\t(using TLSv1.2 with cipher ECDHE-ECDSA-AES256-GCM-SHA384 (256/256 bits))\n\t(No client certificate requested)\n\tby legolas.ozlabs.org (Postfix) with ESMTPS id 4frXfh1tZRz1xv0\n\tfor ; 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