From: Stefano Brivio <sbrivio@redhat.com>
To: David Gibson <david@gibson.dropbear.id.au>,
Laurent Vivier <lvivier@redhat.com>
Cc: passt-dev@passt.top
Subject: Re: [PATCH 1/6] util: Add helper to find offset into io vector
Date: Tue, 27 Feb 2024 15:23:35 +0100 [thread overview]
Message-ID: <20240227152335.75ce9127@elisabeth> (raw)
In-Reply-To: <20240222055602.1872516-2-david@gibson.dropbear.id.au>
On Thu, 22 Feb 2024 16:55:57 +1100
David Gibson <david@gibson.dropbear.id.au> wrote:
> tap_send_frames_passt() needs to determine which buffer element a byte
> offset into an IO vector lies in. We have some upcoming uses for similar
> logic, so split this out into a helper function iov_offset().
>
> Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
> ---
> tap.c | 13 +++++--------
> util.c | 23 +++++++++++++++++++++++
> util.h | 1 +
Laurent, I guess this will need to be moved to iov.h by your series, at
the point where you introduce the new header.
> 3 files changed, 29 insertions(+), 8 deletions(-)
>
> diff --git a/tap.c b/tap.c
> index 396dee7e..f15eba6e 100644
> --- a/tap.c
> +++ b/tap.c
> @@ -390,22 +390,19 @@ static size_t tap_send_frames_passt(const struct ctx *c,
> .msg_iovlen = n,
> };
> unsigned int i;
> + size_t offset;
> ssize_t sent;
>
> sent = sendmsg(c->fd_tap, &mh, MSG_NOSIGNAL | MSG_DONTWAIT);
> if (sent < 0)
> return 0;
>
> - /* Check for any partial frames due to short send */
Why would you drop this comment, though? I feel it's needed even more
as we don't open-code that any longer.
> - for (i = 0; i < n; i++) {
> - if ((size_t)sent < iov[i].iov_len)
> - break;
> - sent -= iov[i].iov_len;
> - }
> + offset = (size_t)sent;
> + i = iov_offset(iov, n, &offset);
I think with these names and interface this becomes quite obscure: it
sounds like 'i' should be an offset at this point... and 'offset', I
have no idea (unless I read the comment to iov_offset()). Slightly
different proposal below.
>
> - if (i < n && sent) {
> + if (i < n && offset) {
> /* A partial frame was sent */
> - tap_send_remainder(c, &iov[i], sent);
> + tap_send_remainder(c, &iov[i], offset);
> i++;
> }
>
> diff --git a/util.c b/util.c
> index 21b35ff9..fb6a0430 100644
> --- a/util.c
> +++ b/util.c
> @@ -574,3 +574,26 @@ int do_clone(int (*fn)(void *), char *stack_area, size_t stack_size, int flags,
> return clone(fn, stack_area + stack_size / 2, flags, arg);
> #endif
> }
> +
> +/* iov_offset() - interpret offset into an IO vector
> + * @iov: IO vector
> + * @n: Number of entries in @iov
> + * @offset: Pointer to offset into IO vector
> + *
> + * Return: index I of iovec which contains the given offset, or @n if
> + * the given offset is >= the total # of bytes in the vector.
> + * *@offset is updated to be the byte offset into (@iov + I),
> + * and is guaranteed to be less than @iov[I].iov_len
> + */
> +size_t iov_offset(const struct iovec *iov, size_t n, size_t *offset)
...what do you think of:
/* iov_entry_index() - Index and optionally entry offset, given global offset
* @iov: IO vector
* @n: Number of entries in @iov
* @global_offset: Global offset of byte in IO vector we're looking for
* @entry_offset: If not NULL, set on return: entry offset
*
* Return: index of IO vector entry for given byte offset, @n if not found
*
* Note: @entry_offset is guaranteed to be less than @iov[i].iov_len, where i is
* the return value
*/
and tap_send_frames_passt() could (more) happily do:
i = iov_entry_index(iov, n, sent, &entry_offset);
if (i < n) {
/* A partial frame was sent */
tap_send_remainder(c, &iov[i], entry_offset);
i++;
}
> +{
> + size_t i;
> +
> + for (i = 0; i < n; i++) {
> + if (*offset < iov[i].iov_len)
Indentation.
> + break;
> + *offset -= iov[i].iov_len;
> + }
> +
> + return i;
> +}
> diff --git a/util.h b/util.h
> index d2320f8c..62fad6fe 100644
> --- a/util.h
> +++ b/util.h
> @@ -229,6 +229,7 @@ void write_pidfile(int fd, pid_t pid);
> 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);
>
> /**
> * mod_sub() - Modular arithmetic subtraction
--
Stefano
next prev parent reply other threads:[~2024-02-27 14:24 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 [this message]
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
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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