- dev - passt

[PATCH] tap: Drop frames if no client connected
by Yumei Huang 18 Sep '25

18 Sep '25

If no client is attached, discard outgoing frames and report them as sent. This mimics the behavior of a physical host with its network cable unplugged. Suggested-by: David Gibson <david(a)gibson.dropbear.id.au> Signed-off-by: Yumei Huang <yuhuang(a)redhat.com> --- tap.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/tap.c b/tap.c index 7ba6399..e01219d 100644 --- a/tap.c +++ b/tap.c @@ -507,13 +507,17 @@ static size_t tap_send_frames_passt(const struct ctx *c, * @iov must have total length @bufs_per_frame * @nframes, with each set of * @bufs_per_frame contiguous buffers representing a single frame. * - * Return: number of frames actually sent + * Return: number of frames actually sent, or accounted as sent */ size_t tap_send_frames(const struct ctx *c, const struct iovec *iov, size_t bufs_per_frame, size_t nframes) { size_t m; + if (c->fd_tap == -1) + /* If no client connected, account the frames have been sent */ + return nframes; + if (!nframes) return 0; -- 2.47.0

3 7

[PATCH v3] Add CONTRIBUTING.md
by Yumei Huang 18 Sep '25

18 Sep '25

Signed-off-by: Yumei Huang <yuhuang(a)redhat.com> --- CONTRIBUTING.md | 152 ++++++++++++++++++++++++++++++++++++++++++++++++ README.md | 4 +- 2 files changed, 155 insertions(+), 1 deletion(-) create mode 100644 CONTRIBUTING.md diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md new file mode 100644 index 0000000..5f41bc3 --- /dev/null +++ b/CONTRIBUTING.md @@ -0,0 +1,152 @@ + + +# Contributing to passt + +Thank you for your interest in contributing! This document explains how +to prepare patches and participate in the email-based review process. + +## Workflow + +### 1. Clone the project + + git clone git://passt.top/passt + +### 2. Make Changes and Commit + +* You can decide to work on the master branch or a separate branch as below: + + cd passt + git checkout -b my-feature-branch + +* Edit the source code or documentation following the + [Linux kernel coding style](https://www.kernel.org/doc/html/latest/process/coding-style.html). + +* Stage your changes: + + git add <file1> <file2> ... + +* Commit with a message: + + git commit + + The message should describe your changes. See + [this link](https://docs.kernel.org/process/submitting-patches.html#describe-your… + for details. Here is an example of commit message format: + + Subsystem: Brief summary + + More detailed explanation if needed, wrapped at 72 chars. + + The `Subsystem` means: which part of the code your change touches. + For example, it could be "tcp", "test", or "doc" etc. + + If there are some references, use "Links:" tag for anything. + + Besides, passt uses the Linux kernel's "Signed-off-by" process. If you can + certify the below: + + Developer's Certificate of Origin 1.1 + + By making a contribution to this project, I certify that: + + (a) The contribution was created in whole or in part by me and I + have the right to submit it under the open source license + indicated in the file; or + + (b) The contribution is based upon previous work that, to the best + of my knowledge, is covered under an appropriate open source + license and I have the right under that license to submit that + work with modifications, whether created in whole or in part + by me, under the same open source license (unless I am + permitted to submit under a different license), as indicated + in the file; or + + (c) The contribution was provided directly to me by some other + person who certified (a), (b) or (c) and I have not modified + it. + + (d) I understand and agree that this project and the contribution + are public and that a record of the contribution (including all + personal information I submit with it, including my sign-off) is + maintained indefinitely and may be redistributed consistent with + this project or the open source license(s) involved. + + Add this line: + + Signed-off-by: Random J Developer <random(a)developer.example.org> + + using your name. This will be done for you automatically if you use + `git commit -s`. Reverts should also include "Signed-off-by". `git + revert -s` does that for you. + + Any further SoBs (Signed-off-by:'s) following the author's SoB are + from people handling and transporting the patch, but were not involved + in its development. SoB chains should reflect the **real** route a + patch took as it was propagated to the maintainers, with the first SoB + entry signalling primary authorship of a single author. + +### 3. Generate Patches + +Use `git format-patch` to generate patch(es): + + git format-patch -o outgoing/ origin/master + +It will generate numbered patch files such as 0001-...patch, 0002-...patch +etc. in the `outgoing` folder. + +Or you can use `git format-patch -n`. For example if you want to format just +three patches: + + git format-patch -3 -o outgoing/ + +If you send a series of patches, use the `--cover-letter` option with +`git format-patch`: + + git format-patch -o outgoing/ origin/main --cover-letter + +This will generate a cover letter besides your patches. Edit the cover +letter before sending. + +### 4. Send Patches + +Use `git send-email` to send patches directly to the mailing list: + + git send-email --to=passt-dev(a)passt.top 000*.patch -o outgoing/000*.patch + +If there are CCs (e.g. maintainers, reviewers), you can add them with `--cc`: + + git send-email --to=passt-dev(a)passt.top --cc=maintainer(a)example.com + outgoing/000*.patch + +### 5. Responding to Review Feedback + +* Be open to feedback on both code and documentation. + +* Update your patch as needed, and regenerate patches: + + git add <file1> <file2> ... + git commit --amend + git format-patch -v2 -o outgoing/ origin/master + +* Send the revised patches: + + git send-email --to=passt-dev(a)passt.top outgoing/v2-000*.patch + +### 6. Tips and Best Practices + +* Keep changes focused and easy to review. Please refer to + [split-changes](https://docs.kernel.org/process/submitting-patches.html#spli… + to separate each logical change into a separate patch. + +* Test your changes thoroughly. Refer to + [test/README.md](/passt/tree/test/README.md) file for testing. + It's recommended to run at least a 'make cppcheck' and 'make clang-tidy' + other than a specific manual test of the functionality / issue at hand. + +* Include documentation updates if your change affects usage. + +Thank you for helping improve passt! Your contributions make a big difference. diff --git a/README.md b/README.md index 8f188f4..897ae8b 100644 --- a/README.md +++ b/README.md @@ -625,7 +625,9 @@ See also the [test logs](/builds/latest/test/). ### [Mailing Lists](/passt/lists) * Submit, review patches, and discuss development ideas on - [`passt-dev`](https://lists.passt.top/postorius/lists/passt-dev.passt.top/) + [`passt-dev`](https://lists.passt.top/postorius/lists/passt-dev.passt.top/). + Please refer to the [CONTRIBUTING.md](/passt/tree/CONTRIBUTING.md) file for + details. * Ask your questions and discuss usage needs on [`passt-user`](https://lists.passt.top/postorius/lists/passt-user.passt.top/) -- 2.47.0

2 1

[PATCH v6 1/5]
by Volker Diels-Grabsch 18 Sep '25

18 Sep '25

This incorporates all feedback of v5, and the commits are slightly reordered so the comment of the last commit makes more sense.

3 11

[PATCH v2] Add CONTRIBUTING.md
by Yumei Huang 18 Sep '25

18 Sep '25

Signed-off-by: Yumei Huang <yuhuang(a)redhat.com> --- CONTRIBUTING.md | 152 ++++++++++++++++++++++++++++++++++++++++++++++++ README.md | 6 +- 2 files changed, 156 insertions(+), 2 deletions(-) create mode 100644 CONTRIBUTING.md diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md new file mode 100644 index 0000000..13fba69 --- /dev/null +++ b/CONTRIBUTING.md @@ -0,0 +1,152 @@ + + +# Contributing to passt + +Thank you for your interest in contributing! This document explains how +to prepare patches and participate in the email-based review process. + +## Workflow + +### 1. Clone the project + + git clone git://passt.top/passt + + +### 3. Make Changes and Commit + +* You can decide to work on the master branch or a separate branch as below: + + cd passt + git checkout -b my-feature-branch + +* Edit the source code or documentation following the [Linux kernel coding style](https://www.kernel.org/doc/html/latest/process/coding-style.html). + + +* Stage your changes: + + git add <file1> <file2> ... + +* Commit with a message. + + git commit + + The message should describe your changes. See [this link](https://docs.kernel.org/process/submitting-patches.html#describe-your… for details. + Here is an example of commit message format: + + Subsystem: Brief summary + + More detailed explanation if needed, wrapped at 72 chars. + + The `Subsystem` means: which part of the code your change touches. + For example, it could be "tcp", "test", and "doc" etc. + + If there are some references, use "Links: " tag for anything. + + Besides, passt uses the Linux kernel's "Signed-off-by" process. If you can + certify the below: + + Developer's Certificate of Origin 1.1 + + By making a contribution to this project, I certify that: + + (a) The contribution was created in whole or in part by me and I + have the right to submit it under the open source license + indicated in the file; or + + (b) The contribution is based upon previous work that, to the best + of my knowledge, is covered under an appropriate open source + license and I have the right under that license to submit that + work with modifications, whether created in whole or in part + by me, under the same open source license (unless I am + permitted to submit under a different license), as indicated + in the file; or + + (c) The contribution was provided directly to me by some other + person who certified (a), (b) or (c) and I have not modified + it. + + (d) I understand and agree that this project and the contribution + are public and that a record of the contribution (including all + personal information I submit with it, including my sign-off) is + maintained indefinitely and may be redistributed consistent with + this project or the open source license(s) involved. + + Add this line: + + Signed-off-by: Random J Developer <random(a)developer.example.org> + + using your real name (sorry, no pseudonyms or anonymous + contributions.) This will be done for you automatically if you use + `git commit -s`. Reverts should also include "Signed-off-by". `git + revert -s` does that for you. + + Any further SoBs (Signed-off-by:'s) following the author's SoB are + from people handling and transporting the patch, but were not involved + in its development. SoB chains should reflect the **real** route a + patch took as it was propagated to the maintainers, with the first SoB + entry signalling primary authorship of a single author. + +### 4. Generate Patches + +Use `git format-path` to generate patch(es): + + git format-patch -o outgoing/ origin/master + +It will generate numbered patch files such as 0001-...patch, 0002-...patch +etc. in the `outgoing` folder. + +Or you can use `git format-patch -n`. For exmaple if you want to format just +three patches: + + git format-patch -3 -o outgoing/ + +If you send a series of patches, use the `--cover-letter` option with +`git format-patch`: + + git format-patch -o outgoing/ origin/main --cover-letter + +This will generate a cover letter besides your patches. You can edit the cover +letter before sending. + +### 5. Send Patches + +Use `git send-email` to send patches directly to the mailing list: + + git send-email --to=passt-dev(a)passt.top 000*.patch -o outgoing/000*.patch + +If there are CCs (e.g. maintainers, reviewers), you can add them with `--cc`: + + git send-email --to=passt-dev(a)passt.top --cc=maintainer(a)example.com + outgoing/000*.patch + +### 6. Responding to Review Feedback + +* Be open to feedback on both code and documentation. + +* Update your patch as needed, and regenerate patches: + + git add <file1> <file2> ... + git commit --amend + git format-patch -v2 origin/master + +* Send the revised patches + + git send-email --to=passt-dev(a)passt.top v2-000*.patch + +### 7. Tips and Best Practices + +* Keep changes focused and easy to review. Please refer to [split-changes](https://docs.kernel.org/process/submitting-patches.html#spli… + to seperate each logical change into a separate patch. + +* Test your changes thoroughly. Refer to [test/README.md](/passt/tree/test/README.md) + for testing. + It's recommended to run at least a 'make cppcheck' and 'make clang-tidy' + other than a specific manual test of the functionality / issue at hand. + +* Include documentation updates if your change affects usage. + +Thank you for helping improve passt! Your contributions make a big difference. diff --git a/README.md b/README.md index 8f188f4..6ba6441 100644 --- a/README.md +++ b/README.md @@ -553,7 +553,7 @@ See also the [test logs](/builds/latest/test/). man ./passt.1 * run the demo script, that detaches user and network namespaces, configures the - new network namespace using `pasta`, starts `passt` and, optionally, `qemu`: + new network namespace using `pasta`, starts `passt` *and, optionally,* `qemu`: doc/demo.sh @@ -625,7 +625,9 @@ See also the [test logs](/builds/latest/test/). ### [Mailing Lists](/passt/lists) * Submit, review patches, and discuss development ideas on - [`passt-dev`](https://lists.passt.top/postorius/lists/passt-dev.passt.top/) + [`passt-dev`](https://lists.passt.top/postorius/lists/passt-dev.passt.top/). + Please refer to the [CONTRIBUTING.md](/passt/tree/CONTRIBUTING.md) for + details. * Ask your questions and discuss usage needs on [`passt-user`](https://lists.passt.top/postorius/lists/passt-user.passt.top/) -- 2.47.0

2 1

[PATCH 1/2] selinux: add container_var_run_t type transition
by Paul Holzinger 17 Sep '25

17 Sep '25

In some cases the podman runroot directory used to be labelled container_var_run_t instead of user_tmp_t which was expected here. Starting with a recent container-selinux change the runroot is now always container_var_run_t so make the policy handle both types to allow for a better upgrade path where passt-selinux and container-selinux are not updated at the same time. Link: https://github.com/containers/container-selinux/pull/405 Link: https://github.com/containers/podman/issues/26473 Signed-off-by: Paul Holzinger <pholzing(a)redhat.com> --- contrib/selinux/pasta.te | 5 +++++ 1 file changed, 5 insertions(+) diff --git a/contrib/selinux/pasta.te b/contrib/selinux/pasta.te index c0a1e9b..24e58c8 100644 --- a/contrib/selinux/pasta.te +++ b/contrib/selinux/pasta.te @@ -96,6 +96,7 @@ require { role staff_r; role user_r; type container_runtime_t; + type container_var_run_t; type container_t; type systemd_user_runtimedir_t; } @@ -242,8 +243,12 @@ type_transition container_runtime_t pasta_exec_t : process pasta_t; allow container_runtime_t pasta_t:process transition; # Label the user network namespace files +# Note podman files used to be user_tmp_t but now are container_var_run_t since +# https://github.com/containers/container-selinux/issues/404. type_transition container_runtime_t user_tmp_t : dir ifconfig_var_run_t "netns"; +type_transition container_runtime_t container_var_run_t : dir ifconfig_var_run_t "netns"; type_transition container_runtime_t user_tmp_t : dir ifconfig_var_run_t "rootless-netns"; +type_transition container_runtime_t container_var_run_t : dir ifconfig_var_run_t "rootless-netns"; allow pasta_t ifconfig_var_run_t:dir { add_name open rmdir write }; allow pasta_t ifconfig_var_run_t:file { create open write }; allow systemd_user_runtimedir_t ifconfig_var_run_t:dir rmdir; -- 2.51.0

2 4

[PATCH] dhcp: Fix coding style violations in dhcp() function
by Laurent Vivier 17 Sep '25

17 Sep '25

The dhcp() function wasn't following the inverted Christmas tree variable declaration ordering convention. Signed-off-by: Laurent Vivier <lvivier(a)redhat.com> --- dhcp.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/dhcp.c b/dhcp.c index 012cec6c0d04..6b9c2e3b9e5a 100644 --- a/dhcp.c +++ b/dhcp.c @@ -311,10 +311,10 @@ int dhcp(const struct ctx *c, struct iov_tail *data) const struct ethhdr *eh; const struct iphdr *iph; const struct udphdr *uh; + struct msg m_storage; struct msg const *m; struct msg reply; unsigned int i; - struct msg m_storage; eh = IOV_REMOVE_HEADER(data, eh_storage); iph = IOV_PEEK_HEADER(data, iph_storage); -- 2.50.1

2 1

[PATCH] Add CONTRIBUTING.md
by Yumei Huang 17 Sep '25

17 Sep '25

Signed-off-by: Yumei Huang <yuhuang(a)redhat.com> --- CONTRIBUTING.md | 86 +++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 86 insertions(+) create mode 100644 CONTRIBUTING.md diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md new file mode 100644 index 0000000..70e35b1 --- /dev/null +++ b/CONTRIBUTING.md @@ -0,0 +1,86 @@ +# Contributing to passt + +Thank you for your interest in contributing! This document explains how to prepare patches and participate in the email-based review process. + +## Workflow + +### 1. Clone the project + + git clone git://passt.top/passt + +### 2. Create a Branch + + cd passt + git checkout -b my-feature-branch + +Work on a separate branch instead of committing directly to `master`. + +### 3. Make Changes and Commit + +* Edit the source code or documentation. + +* Stage your changes: + + git add <file1> <file2> ... + +* Commit with a clear message containing `Signed-off-by:` tag: + + git commit -s + + Commit message format: + + Subsystem: Brief summary (max ~50 chars) + + More detailed explanation if needed, wrapped at 72 chars. + + Signed-off-by: Your Name <author@email> + + If there are some references, use "Links: " tag for simplicity. + +### 4. Generate Patches + +Use `git format-path` to generate patch(es): + + git format-patch origin/master + +This will generate numbered patch files such as 0001-...patch, 0002-...patch, etc. + +If you send a series of patches, use the `--cover-letter` option with `git format-patch`: + + git format-patch origin/main --cover-letter + +This will generate a cover letter besides your patches. You can edit the cover letter before sending. + +### 5. Send Patches + +Use `git send-email` to send patches directly to the mailing list: + + git send-email --to=passt-dev(a)passt.top 000*.patch + +If there are CCs (e.g. maintainers, reviewers), you can add them with `--cc`: + + git send-email --to=passt-dev(a)passt.top --cc=maintainer(a)example.com 000*.patch + +### 6. Responding to Review Feedback + +* Be open to feedback on both code and documentation. + +* Update your patch as needed, and regenerate patches: + + git add <file1> <file2> ... + git commit --amend + git format-patch -v2 origin/master + +* Send the revised patches + + git send-email --to=passt-dev(a)passt.top v2-000*.patch + +### 7. Tips and Best Practices + +* Keep changes focused and easy to review. + +* Test your changes thoroughly. + +* Include documentation updates if your change affects usage or APIs. + +Thank you for helping improve passt! Your contributions make a big difference. -- 2.47.0

3 3

[PATCH v5 1/5] Show debug message whenever we learn a new guest MAC address
by Volker Diels-Grabsch 16 Sep '25

16 Sep '25

Signed-off-by: Volker Diels-Grabsch <v(a)njh.eu> --- tap.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/tap.c b/tap.c index 7ba6399..3c08126 100644 --- a/tap.c +++ b/tap.c @@ -1096,7 +1096,11 @@ void tap_add_packet(struct ctx *c, struct iov_tail *data, return; if (memcmp(c->guest_mac, eh->h_source, ETH_ALEN)) { + char bufmac[ETH_ADDRSTRLEN]; + memcpy(c->guest_mac, eh->h_source, ETH_ALEN); + debug("Guest MAC address: %s", + eth_ntop(c->guest_mac, bufmac, sizeof(bufmac))); proto_update_l2_buf(c->guest_mac, NULL); } -- 2.47.3

3 12

[PATCH] Reduce tcp_buf_discard size
by xugu＠redhat.com 15 Sep '25

15 Sep '25

From: Xun Gu <xugu(a)redhat.com> On kernels without SO_PEEK_OFF, a 16MB static buffer is used to discard sent data. This patch reduces the buffer to 1MB. Larger discards are now handled by using multiple iovec entries pointing to the same 1MB buffer. Signed-off-by: Xun Gu <xugu(a)redhat.com> --- tcp.c | 66 +++++++++++++++++++++++++++++++++++++++++++++++++- tcp_buf.c | 18 +++++--------- tcp_internal.h | 7 +++++- tcp_vu.c | 17 ++++--------- 4 files changed, 82 insertions(+), 26 deletions(-) diff --git a/tcp.c b/tcp.c index a27b069..253cdb3 100644 --- a/tcp.c +++ b/tcp.c @@ -399,7 +399,7 @@ static int tcp_sock_ns [NUM_PORTS][IP_VERSIONS]; */ static union inany_addr low_rtt_dst[LOW_RTT_TABLE_SIZE]; -char tcp_buf_discard [MAX_WINDOW]; +char tcp_buf_discard [BUF_DISCARD_SIZE]; /* Does the kernel support TCP_PEEK_OFF? */ bool peek_offset_cap; @@ -3766,3 +3766,67 @@ fail: return 0; } + +/** + * tcp_prepare_iov() - Prepare iov according to kernel capability + * @msg: Message header to update + * @iov: iovec to receive TCP payload and data to discard + * @already_sent: Bytes sent after the last acknowledged one + * @payload_iov_cnt: Number of TCP payload iovec entries + * + * Return: 0 on success, -1 if already_sent cannot be discarded fully + */ +int tcp_prepare_iov(struct msghdr *msg, struct iovec *iov, + uint32_t already_sent, int payload_iov_cnt) +{ + /* + * IOV layout + * |- tcp_buf_discard -|---------- TCP data slots ------------| + * + * with discarded data: + * |------ddddddddddddd|ttttttttttttt-------------------------| + * ^ + * | + * msg_iov + * + * without discarded data: + * |-------------------|ttttttttttttt-------------------------| + * ^ + * | + * msg_iov + * d: discard data + * t: TCP data + */ + if (peek_offset_cap) { + msg->msg_iov = iov + DISCARD_IOV_NUM; + msg->msg_iovlen = payload_iov_cnt; + } else { + int discard_cnt, discard_iov_rem; + struct iovec *iov_start; + int i; + + discard_cnt = DIV_ROUND_UP(already_sent, BUF_DISCARD_SIZE); + if (discard_cnt > DISCARD_IOV_NUM) { + debug("Failed to discard %u already sent bytes", + already_sent); + return -1; + } + + discard_iov_rem = already_sent % BUF_DISCARD_SIZE; + + iov_start = iov + (DISCARD_IOV_NUM - discard_cnt); + + /* Multiple iov entries pointing to the same buffer */ + for (i = 0; i < discard_cnt; i++) { + iov_start[i].iov_base = tcp_buf_discard; + iov_start[i].iov_len = BUF_DISCARD_SIZE; + } + if (discard_iov_rem) + iov[DISCARD_IOV_NUM - 1].iov_len = discard_iov_rem; + + msg->msg_iov = iov_start; + msg->msg_iovlen = discard_cnt + payload_iov_cnt; + } + + return 0; +} diff --git a/tcp_buf.c b/tcp_buf.c index bc898de..4ebb013 100644 --- a/tcp_buf.c +++ b/tcp_buf.c @@ -60,7 +60,7 @@ static struct tcp_tap_conn *tcp_frame_conns[TCP_FRAMES_MEM]; static unsigned int tcp_payload_used; /* recvmsg()/sendmsg() data for tap */ -static struct iovec iov_sock [TCP_FRAMES_MEM + 1]; +static struct iovec iov_sock [TCP_FRAMES_MEM + DISCARD_IOV_NUM]; static struct iovec tcp_l2_iov[TCP_FRAMES_MEM][TCP_NUM_IOVS]; @@ -326,15 +326,9 @@ int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) iov_rem = (wnd_scaled - already_sent) % mss; } - /* Prepare iov according to kernel capability */ - if (!peek_offset_cap) { - mh_sock.msg_iov = iov_sock; - iov_sock[0].iov_base = tcp_buf_discard; - iov_sock[0].iov_len = already_sent; - mh_sock.msg_iovlen = fill_bufs + 1; - } else { - mh_sock.msg_iov = &iov_sock[1]; - mh_sock.msg_iovlen = fill_bufs; + if (tcp_prepare_iov(&mh_sock, iov_sock, already_sent, fill_bufs)) { + tcp_rst(c, conn); + return -1; } if (tcp_payload_used + fill_bufs > TCP_FRAMES_MEM) { @@ -344,12 +338,12 @@ int tcp_buf_data_from_sock(const struct ctx *c, struct tcp_tap_conn *conn) tcp_payload_used = 0; } - for (i = 0, iov = iov_sock + 1; i < fill_bufs; i++, iov++) { + for (i = 0, iov = iov_sock + DISCARD_IOV_NUM; i < fill_bufs; i++, iov++) { iov->iov_base = &tcp_payload[tcp_payload_used + i].data; iov->iov_len = mss; } if (iov_rem) - iov_sock[fill_bufs].iov_len = iov_rem; + iov_sock[fill_bufs + DISCARD_IOV_NUM - 1].iov_len = iov_rem; /* Receive into buffers, don't dequeue until acknowledged by guest. */ do diff --git a/tcp_internal.h b/tcp_internal.h index 9dae688..d0009f8 100644 --- a/tcp_internal.h +++ b/tcp_internal.h @@ -9,6 +9,9 @@ #define MAX_WS 8 #define MAX_WINDOW (1 << (16 + (MAX_WS))) +#define BUF_DISCARD_SIZE (1 << 20) +#define DISCARD_IOV_NUM DIV_ROUND_UP(MAX_WINDOW, BUF_DISCARD_SIZE) + #define MSS4 ROUND_DOWN(IP_MAX_MTU - \ sizeof(struct tcphdr) - \ sizeof(struct iphdr), \ @@ -139,7 +142,7 @@ struct tcp_syn_opts { .ws = TCP_OPT_WS(ws_), \ }) -extern char tcp_buf_discard [MAX_WINDOW]; +extern char tcp_buf_discard [BUF_DISCARD_SIZE]; void conn_flag_do(const struct ctx *c, struct tcp_tap_conn *conn, unsigned long flag); @@ -180,4 +183,6 @@ int tcp_prepare_flags(const struct ctx *c, struct tcp_tap_conn *conn, size_t *optlen); int tcp_set_peek_offset(const struct tcp_tap_conn *conn, int offset); +int tcp_prepare_iov(struct msghdr *msg, struct iovec *iov, + uint32_t already_sent, int payload_iov_cnt); #endif /* TCP_INTERNAL_H */ diff --git a/tcp_vu.c b/tcp_vu.c index cb39bc2..097ca13 100644 --- a/tcp_vu.c +++ b/tcp_vu.c @@ -35,7 +35,7 @@ #include "vu_common.h" #include <time.h> -static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE + 1]; +static struct iovec iov_vu[VIRTQUEUE_MAX_SIZE + DISCARD_IOV_NUM]; static struct vu_virtq_element elem[VIRTQUEUE_MAX_SIZE]; static int head[VIRTQUEUE_MAX_SIZE + 1]; @@ -200,7 +200,7 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, hdrlen = tcp_vu_hdrlen(v6); - vu_init_elem(elem, &iov_vu[1], VIRTQUEUE_MAX_SIZE); + vu_init_elem(elem, &iov_vu[DISCARD_IOV_NUM], VIRTQUEUE_MAX_SIZE); elem_cnt = 0; *head_cnt = 0; @@ -228,16 +228,9 @@ static ssize_t tcp_vu_sock_recv(const struct ctx *c, elem_cnt += cnt; } - if (peek_offset_cap) { - mh_sock.msg_iov = iov_vu + 1; - mh_sock.msg_iovlen = elem_cnt; - } else { - iov_vu[0].iov_base = tcp_buf_discard; - iov_vu[0].iov_len = already_sent; - - mh_sock.msg_iov = iov_vu; - mh_sock.msg_iovlen = elem_cnt + 1; - } + if (tcp_prepare_iov(&mh_sock, iov_vu, already_sent, elem_cnt)) + /* Expect caller to do a TCP reset */ + return -1; do ret = recvmsg(s, &mh_sock, MSG_PEEK); -- 2.51.0

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[PATCH v2] tap: Drop frames if no client connected
by Yumei Huang 15 Sep '25

15 Sep '25

If no client is attached, discard outgoing frames and report them as sent. Without this we will get an EBADF in either writev() (pasta) or sendmsg() (passt). That's basically harmless, but a bit ugly. Explicitly catching this case results in behaviour that's probably a bit clearer to debug if we hit it. There are several different approaches we can take here. Here's some reasoning as David explained: * Don't listen() until the tap connection is ready - It's not clear that the host rejecting the connection is better than the host accepting, then the connection stalling until the guest is ready. - Would require substantial rework because we currently listen() as we parse the command line and don't store the information we'd need to do it later. * Don't accept() until the tap connection is ready - To the peer, will behave basically the same as this patch - the host will complete the TCP handshake, then the connection will stall until the guest is ready. - More work to implement, because essentially every sock-side handler has to check fd_tap and abort early * Drop packets in tap_send_frames(), but return 0 - To the peer, would behave basically the same - Would make the TCP code do a bunch of busy work attempting to resend, probably to no avail - Handling of errors returned by tap_send_frames() is on the basis that it's probably a transient fault (buffer full) and we want to resend very soon. That approach doesn't make sense for a missing guest. Suggested-by: David Gibson <david(a)gibson.dropbear.id.au> Signed-off-by: Yumei Huang <yuhuang(a)redhat.com> --- tap.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/tap.c b/tap.c index 7ba6399..2e371b3 100644 --- a/tap.c +++ b/tap.c @@ -507,13 +507,16 @@ static size_t tap_send_frames_passt(const struct ctx *c, * @iov must have total length @bufs_per_frame * @nframes, with each set of * @bufs_per_frame contiguous buffers representing a single frame. * - * Return: number of frames actually sent + * Return: number of frames actually sent, or accounted as sent */ size_t tap_send_frames(const struct ctx *c, const struct iovec *iov, size_t bufs_per_frame, size_t nframes) { size_t m; + if (c->fd_tap == -1) + return nframes; + if (!nframes) return 0; -- 2.47.0

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