Re: [PATCH v2 2/7] iov: Add helper to find skip over first n bytes of an io vector

[David Gibson <david@gibson.dropbear.id.au>]

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On Thu, Feb 29, 2024 at 09:10:02AM +0100, Stefano Brivio wrote:
> On Wed, 28 Feb 2024 12:52:01 +1100
> David Gibson <david@gibson.dropbear.id.au> wrote:
> 
> > Several of the IOV functions in iov.c, and also tap_send_frames_passt()
> > needs to determine which buffer element a byte offset into an IO vector
> > lies in.  Split this out into a helper function iov_skip_bytes().
> > 
> > Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> > ---
> >  iov.c | 42 +++++++++++++++++++++++++++++++++---------
> >  iov.h |  2 ++
> >  tap.c | 12 +++++-------
> >  3 files changed, 40 insertions(+), 16 deletions(-)
> > 
> > diff --git a/iov.c b/iov.c
> > index 8a48acb1..e3312628 100644
> > --- a/iov.c
> > +++ b/iov.c
> > @@ -25,6 +25,36 @@
> >  #include "util.h"
> >  #include "iov.h"
> >  
> > +
> > +/* iov_skip_bytes() - Skip the first n bytes into an IO vector
> > + * @iov:	IO vector
> > + * @n:		Number of entries in @iov
> 
> ...which is a different 'n' compared to two lines above.

Ouch, good point.

> > + * @vec_offset: Total byte offset into the IO vector
> 
> This doesn't clearly correlate with the description of the function
> ("first n bytes").
> 
> Same here, I have no other comments about the series, so I'll
> apply this and try to improve this a bit as a follow-up.

Ok, thanks.  I might see if I can improve this one too.

> 
> > + * @buf_offset:	Offset into a single buffer of the IO vector
> > + *
> > + * Return: index I of individual struct iovec which contains the byte at
> > + *         @vec_offset bytes into the vector (as though all its buffers were
> > + *         contiguous).  If @buf_offset is non-NULL, update it to the offset of
> > + *         that byte within @iov[I] (guaranteed to be less than @iov[I].iov_len)
> > + *	   If the whole vector has <= @vec_offset bytes, return @n.
> > + */
> > +size_t iov_skip_bytes(const struct iovec *iov, size_t n,
> > +		      size_t vec_offset, size_t *buf_offset)
> 

-- 
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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