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