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[164.138.29.33]) by smtp.gmail.com with ESMTPSA id o24-20020aa7c7d8000000b0055c60ba9640sm802946eds.77.2024.02.27.06.24.08 (version=TLS1_2 cipher=ECDHE-ECDSA-AES128-GCM-SHA256 bits=128/128); Tue, 27 Feb 2024 06:24:08 -0800 (PST) Date: Tue, 27 Feb 2024 15:23:35 +0100 From: Stefano Brivio To: David Gibson , Laurent Vivier Subject: Re: [PATCH 1/6] util: Add helper to find offset into io vector Message-ID: <20240227152335.75ce9127@elisabeth> In-Reply-To: <20240222055602.1872516-2-david@gibson.dropbear.id.au> References: <20240222055602.1872516-1-david@gibson.dropbear.id.au> <20240222055602.1872516-2-david@gibson.dropbear.id.au> Organization: Red Hat X-Mailer: Claws Mail 4.2.0 (GTK 3.24.36; x86_64-pc-linux-gnu) MIME-Version: 1.0 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Message-ID-Hash: GGL3AMGUYXQLQL55NAM5GQZPUPK74KLF X-Message-ID-Hash: GGL3AMGUYXQLQL55NAM5GQZPUPK74KLF X-MailFrom: sbrivio@redhat.com X-Mailman-Rule-Misses: dmarc-mitigation; no-senders; approved; emergency; loop; banned-address; member-moderation; nonmember-moderation; administrivia; implicit-dest; max-recipients; max-size; news-moderation; no-subject; digests; suspicious-header CC: passt-dev@passt.top X-Mailman-Version: 3.3.8 Precedence: list List-Id: Development discussion and patches for passt Archived-At: Archived-At: List-Archive: List-Archive: List-Help: List-Owner: List-Post: List-Subscribe: List-Unsubscribe: On Thu, 22 Feb 2024 16:55:57 +1100 David Gibson 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 > --- > 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