From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH v2 18/18] tap: Improve handling of partial frame sends
Date: Thu, 5 Jan 2023 15:57:21 +1100 [thread overview]
Message-ID: <Y7ZYsZxiUY8+7Llz@yekko> (raw)
In-Reply-To: <20230104184533.0f9ea7b4@elisabeth>
[-- Attachment #1: Type: text/plain, Size: 2242 bytes --]
On Wed, Jan 04, 2023 at 06:45:33PM +0100, Stefano Brivio wrote:
> On Fri, 9 Dec 2022 16:42:28 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
>
> > In passt mode, when writing frames to the qemu socket, we might get a short
> > send. If we ignored this and carried on, the qemu socket would get out of
> > sync, because the bytes we actually sent wouldn't correspond to the length
> > header we already sent. tap_send_frames_passt() handles that by doing a
> > a blocking send to complete the message, but it has a few flaws:
> > * We only attempt to resend once: although it's unlikely in practice,
> > nothing prevents the blocking send() from also being short
> > * We print a debug error if send() returns non-zero.. but send() returns
> > the number of bytes sent, so we actually want it to return the length
> > of the remaining data.
> >
> > Correct those flaws and also be a bit more thorough about reporting
> > problems here.
> >
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> > tap.c | 51 ++++++++++++++++++++++++++++++++++++++-------------
> > 1 file changed, 38 insertions(+), 13 deletions(-)
> >
> > diff --git a/tap.c b/tap.c
> > index 5ec6b70..4fb27ca 100644
> > --- a/tap.c
> > +++ b/tap.c
> > @@ -326,13 +326,39 @@ static void tap_send_frames_pasta(struct ctx *c,
> > }
> > }
> >
> > +/**
> > + * tap_send_remainder() - Send remainder of a partiall sent frame
>
> s/partiall/partially/
Fixed.
> > + * @c: Execution context
> > + * @iov: Partially sent buffer
> > + * @offset: Number of bytes already sent from @iov
> > + *
> > + * #syscalls:passt sendto
>
> We should probably drop this, it's actually send(2) on armv6/armv7 and
> ppc64le, sendto(2) otherwise -- initially I sprinkled those annotations
> all over the place to show where specific calls were issued (and make
> it easier to drop them from the filter if calls disappeared) but I
> think it's not really practical for send(3).
Heh, right. Done.
--
David Gibson | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au | minimalist, thank you. NOT _the_ _other_
| _way_ _around_!
http://www.ozlabs.org/~dgibson
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2023-01-05 5:45 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-12-09 5:42 [PATCH v2 00/18] RFC: Unify and simplify tap send path David Gibson
2022-12-09 5:42 ` [PATCH v2 01/18] pcap: Introduce pcap_frame() helper David Gibson
2023-01-04 17:45 ` Stefano Brivio
2023-01-05 4:47 ` David Gibson
2022-12-09 5:42 ` [PATCH v2 02/18] pcap: Replace pcapm() with pcap_multiple() David Gibson
2022-12-09 5:42 ` [PATCH v2 03/18] tcp: Combine two parts of passt tap send path together David Gibson
2022-12-09 5:42 ` [PATCH v2 04/18] tcp: Don't keep compute total bytes in a message until we need it David Gibson
2023-01-04 17:45 ` Stefano Brivio
2023-01-05 4:48 ` David Gibson
2022-12-09 5:42 ` [PATCH v2 05/18] tcp: Improve interface to tcp_l2_buf_flush() David Gibson
2023-01-04 17:45 ` Stefano Brivio
2023-01-05 4:53 ` David Gibson
2022-12-09 5:42 ` [PATCH v2 06/18] tcp: Combine two parts of pasta tap send path together David Gibson
2022-12-09 5:42 ` [PATCH v2 07/18] tap, tcp: Move tap send path to tap.c David Gibson
2022-12-09 5:42 ` [PATCH v2 08/18] util: Introduce hton*_constant() in place of #ifdefs David Gibson
2022-12-09 5:42 ` [PATCH v2 09/18] tcp, udp: Use named field initializers in iov_init functions David Gibson
2022-12-09 5:42 ` [PATCH v2 10/18] util: Parameterize ethernet header initializer macro David Gibson
2022-12-09 5:42 ` [PATCH v2 11/18] tcp: Remove redundant and incorrect initialization from *_iov_init() David Gibson
2022-12-09 5:42 ` [PATCH v2 12/18] tcp: Consolidate calculation of total frame size David Gibson
2022-12-09 5:42 ` [PATCH v2 13/18] tap: Add "tap headers" abstraction David Gibson
2022-12-09 5:42 ` [PATCH v2 14/18] tcp: Use abstracted tap header David Gibson
2022-12-09 5:42 ` [PATCH v2 15/18] tap: Use different io vector bases depending on tap type David Gibson
2022-12-09 5:42 ` [PATCH v2 16/18] udp: Use abstracted tap header David Gibson
2022-12-09 5:42 ` [PATCH v2 17/18] udp: Use tap_send_frames() David Gibson
2023-01-04 17:45 ` Stefano Brivio
2023-01-05 4:54 ` David Gibson
2022-12-09 5:42 ` [PATCH v2 18/18] tap: Improve handling of partial frame sends David Gibson
2023-01-04 17:45 ` Stefano Brivio
2023-01-05 4:57 ` David Gibson [this message]
2023-01-04 17:45 ` [PATCH v2 00/18] RFC: Unify and simplify tap send path Stefano Brivio
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Y7ZYsZxiUY8+7Llz@yekko \
--to=david@gibson.dropbear.id.au \
--cc=passt-dev@passt.top \
--cc=sbrivio@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://passt.top/passt
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for IMAP folder(s).