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From: David Gibson <david@gibson.dropbear.id.au>
To: Markus Armbruster <armbru@redhat.com>
Cc: passt-dev@passt.top, Stefano Brivio <sbrivio@redhat.com>
Subject: Re: [PATCH v2 1/2] util: Add helper to write() all of a buffer
Date: Wed, 18 Sep 2024 20:22:59 +1000	[thread overview]
Message-ID: <ZuqqA0ntGUCgzrQY@zatzit.fritz.box> (raw)
In-Reply-To: <878qvp4huh.fsf@pond.sub.org>

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On Wed, Sep 18, 2024 at 08:05:26AM +0200, Markus Armbruster wrote:
> David Gibson <david@gibson.dropbear.id.au> writes:
> 
> > write(2) might not write all the data it is given.  Add a write_all_buf()
> > helper to keep calling it until all the given data is written, or we get an
> > error.
> >
> > Currently we use write_remainder() to do this operation in pcap_frame().
> > That's a little awkward since it requires constructing an iovec, and future
> > changes we want to make to write_remainder() will be easier in terms of
> > this single buffer helper.
> >
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  pcap.c |  3 +--
> >  util.c | 25 +++++++++++++++++++++++++
> >  util.h |  1 +
> >  3 files changed, 27 insertions(+), 2 deletions(-)
> >
> > diff --git a/pcap.c b/pcap.c
> > index 46cc4b0d..e6b5ced4 100644
> > --- a/pcap.c
> > +++ b/pcap.c
> > @@ -86,9 +86,8 @@ static void pcap_frame(const struct iovec *iov, size_t iovcnt,
> >  		.caplen = l2len,
> >  		.len = l2len
> >  	};
> > -	struct iovec hiov = { &h, sizeof(h) };
> >  
> > -	if (write_remainder(pcap_fd, &hiov, 1, 0) < 0 ||
> > +	if (write_all_buf(pcap_fd, &h, sizeof(h)) < 0 ||
> >  	    write_remainder(pcap_fd, iov, iovcnt, offset) < 0)
> >  		debug_perror("Cannot log packet, length %zu", l2len);
> >  }
> > diff --git a/util.c b/util.c
> > index eede4e58..7db7c2e7 100644
> > --- a/util.c
> > +++ b/util.c
> > @@ -582,6 +582,31 @@ int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
> >  #endif
> >  }
> >  
> > +/* write_all_buf() - write all of a buffer to an fd
> > + * @fd:		File descriptor
> > + * @buf:	Pointer to base of buffer
> > + * @len:	Length of buffer
> > + *
> > + * Return: 0 on success, -1 on error (with errno set)
> > + *
> > + * #syscalls write
> > + */
> > +int write_all_buf(int fd, const void *buf, size_t len)
> 
> I'd call it write_all(), but that's strictly a matter of taste.

I usually would too, but given we work pretty heavily with both plain
buffers and iovs, I thought it was worth emphasising that this works
on the former.

> > +{
> > +	const char *p = buf;
> > +	size_t left = len;
> > +
> > +	while (left) {
> > +		ssize_t rc = write(fd, p, left);
> > +
> > +		if (rc < 0)
> > +			return -1;
> 
> Loop when errno == EINTR?

Oh, good idea.

-- 
David Gibson (he or they)	| 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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  reply	other threads:[~2024-09-18 10:39 UTC|newest]

Thread overview: 7+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-09-17  6:45 [PATCH v2 0/2] util: Fix some problems in write_remainder() David Gibson
2024-09-17  6:45 ` [PATCH v2 1/2] util: Add helper to write() all of a buffer David Gibson
2024-09-18  6:05   ` Markus Armbruster
2024-09-18 10:22     ` David Gibson [this message]
2024-09-17  6:45 ` [PATCH v2 2/2] util: Remove possible quadratic behaviour from write_remainder() David Gibson
2024-09-18  6:20   ` Markus Armbruster
2024-09-18 10:27     ` David Gibson

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