From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top, Laurent Vivier <lvivier@redhat.com>
Subject: Re: [PATCH 3/6] util: Add write_remainder() helper
Date: Wed, 28 Feb 2024 11:44:28 +1100 [thread overview]
Message-ID: <Zd6B7IpsZJbEu5GA@zatzit> (raw)
In-Reply-To: <20240227152551.72d8744f@elisabeth>
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On Tue, Feb 27, 2024 at 03:25:51PM +0100, Stefano Brivio wrote:
> On Thu, 22 Feb 2024 16:55:59 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
>
> > We have several places where we want to write(2) a buffer or buffers and we
> > do (or should) handle sort write()s by retrying until everything is
>
> After making sure that "handle sorting" doesn't exist (yet): is one
> between "handle" and "sort" redundant, or is there another meaning to
> this?
Oops. s/sort/short/ is what makes this make sense.
>
> > successfully written. Add a helper for this in util.c.
> >
> > This version has some differences from the typical write_all() function.
> > First, take an IO vector rather than a single buffer, because that will be
> > useful for some of our cases. Second, allow it to take an parameter to
> > skip the first n bytes of the given buffers. This will be usefl for some
> > of the cases we want, and also falls out quite naturally from the
> > implementation.
> >
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> > util.c | 32 ++++++++++++++++++++++++++++++++
> > util.h | 1 +
> > 2 files changed, 33 insertions(+)
> >
> > diff --git a/util.c b/util.c
> > index fb6a0430..a475f2b5 100644
> > --- a/util.c
> > +++ b/util.c
> > @@ -19,6 +19,7 @@
> > #include <arpa/inet.h>
> > #include <net/ethernet.h>
> > #include <sys/epoll.h>
> > +#include <sys/uio.h>
> > #include <fcntl.h>
> > #include <string.h>
> > #include <time.h>
> > @@ -597,3 +598,34 @@ size_t iov_offset(const struct iovec *iov, size_t n, size_t *offset)
> >
> > return i;
> > }
> > +
> > +/* write_remainder() - write the tail of an IO vector to an fd
> > + * @fd: File descriptor
> > + * @iov: IO vector
> > + * @iovcnt: Number of entries in @iov
> > + * @skip: Number of bytes of the vector to skip writing
> > + *
> > + * Return: 0 on success, -1 on error (with errno set)
> > + *
> > + * #syscalls write writev
> > + */
> > +int write_remainder(int fd, const struct iovec *iov, int iovcnt, size_t skip)
> > +{
> > + int i;
> > +
> > + while ((i = iov_offset(iov, iovcnt, &skip)) < iovcnt) {
>
> With my proposal for 1/6 this becomes:
>
> while ((i = iov_entry_index(iov, iovcnt, skip, &offset)) < iovcnt) {
Hrm, the easiest conversion is to use (..., skip, &skip). Using a new
variable means we'd need to feed that back into skip somehow on the
next loop.
>
> if (offset)
> ...
>
> which I don't really find brilliant, but at least we don't do if (skip)
> where 'skip' used to be something completely different.
So.. the version I have now you might not like based on this comment,
because it still has 'skip' essentially become a local variable with a
different meaning from the one it has at entry.
> > + ssize_t rc;
> > +
> > + if (skip)
>
> Curly brackets here for consistency (undecided about readability to be
> honest).
Uh.. consistency with what? We don't typically brace single line
clauses in passt.
>
> > + rc = write(fd, (char *)iov[i].iov_base + skip,
> > + iov[i].iov_len - skip);
> > + else
> > + rc = writev(fd, &iov[i], iovcnt - i);
> > +
> > + if (rc < 0)
> > + return -1;
> > + skip += rc;
> > + }
> > +
> > + return 0;
> > +}
> > diff --git a/util.h b/util.h
> > index 62fad6fe..ee380f55 100644
> > --- a/util.h
> > +++ b/util.h
> > @@ -230,6 +230,7 @@ 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);
> > +int write_remainder(int fd, const struct iovec *iov, int iovcnt, size_t skip);
> >
> > /**
> > * mod_sub() - Modular arithmetic subtraction
>
--
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
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next prev parent reply other threads:[~2024-02-28 1:02 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 ` [PATCH 1/6] util: Add helper to find offset into io vector David Gibson
2024-02-27 14:23 ` 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 [this message]
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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