From: David Gibson <david@gibson.dropbear.id.au>
To: Stefano Brivio <sbrivio@redhat.com>
Cc: passt-dev@passt.top, Laurent Vivier <lvivier@redhat.com>
Subject: Re: [PATCH v2 4/8] util: Add read_remainder() and read_all_buf()
Date: Wed, 29 Jan 2025 12:37:40 +1100 [thread overview]
Message-ID: <Z5mGZIBnsYG9IEr8@zatzit> (raw)
In-Reply-To: <20250128233940.1235855-5-sbrivio@redhat.com>
[-- Attachment #1: Type: text/plain, Size: 4121 bytes --]
On Wed, Jan 29, 2025 at 12:39:36AM +0100, Stefano Brivio wrote:
> These are symmetric to write_remainder() and write_all_buf() and
> almost a copy and paste of them, with the most notable differences
> being reversed reads/writes and a couple of better-safe-than-sorry
> asserts to keep Coverity happy.
>
> I'll use them in the next patch. At least for the moment, they're
> going to be used for vhost-user mode only, so I'm not unconditionally
> enabling readv() in the seccomp profile: the caller has to ensure it's
> there.
>
> Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Reviewed-by: David Gibson <david@gibson.dropbear.id.au>
I don't think I've ever encountered ENODATA before, so it seems a good
choice. Other options would be
a) 0 for success, -ve for read error, 1 for EOF
b) -ve for read error, 0 for EOF, # of bytes for success (redundant,
but harmless)
but this is fine.
> ---
> util.c | 80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> util.h | 2 ++
> 2 files changed, 82 insertions(+)
>
> diff --git a/util.c b/util.c
> index 11973c4..36857d4 100644
> --- a/util.c
> +++ b/util.c
> @@ -606,6 +606,86 @@ int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip)
> return 0;
> }
>
> +/**
> + * read_all_buf() - Fill a whole buffer from a file descriptor
> + * @fd: File descriptor
> + * @buf: Pointer to base of buffer
> + * @len: Length of buffer
> + *
> + * Return: 0 on success, -1 on error (with errno set)
> + *
> + * #syscalls read
> + */
> +int read_all_buf(int fd, void *buf, size_t len)
> +{
> + size_t left = len;
> + char *p = buf;
> +
> + while (left) {
> + ssize_t rc;
> +
> + ASSERT(left <= len);
> +
> + do
> + rc = read(fd, p, left);
> + while ((rc < 0) && errno == EINTR);
> +
> + if (rc < 0)
> + return -1;
> +
> + if (rc == 0) {
> + errno = ENODATA;
> + return -1;
> + }
> +
> + p += rc;
> + left -= rc;
> + }
> + return 0;
> +}
> +
> +/**
> + * read_remainder() - Read the tail of an IO vector from a file descriptor
> + * @fd: File descriptor
> + * @iov: IO vector
> + * @cnt: Number of entries in @iov
> + * @skip: Number of bytes of the vector to skip reading
> + *
> + * Return: 0 on success, -1 on error (with errno set)
> + *
> + * Note: mode-specific seccomp profiles need to enable readv() to use this.
> + */
> +int read_remainder(int fd, struct iovec *iov, size_t cnt, size_t skip)
> +{
> + size_t i = 0, offset;
> +
> + while ((i += iov_skip_bytes(iov + i, cnt - i, skip, &offset)) < cnt) {
> + ssize_t rc;
> +
> + if (offset) {
> + ASSERT(offset < iov[i].iov_len);
> + /* Read the remainder of the partially read buffer */
> + if (read_all_buf(fd, (char *)iov[i].iov_base + offset,
> + iov[i].iov_len - offset) < 0)
> + return -1;
> + i++;
> + }
> +
> + /* Fill as many of the remaining buffers as we can */
> + rc = readv(fd, &iov[i], cnt - i);
> + if (rc < 0)
> + return -1;
> +
> + if (rc == 0) {
> + errno = ENODATA;
> + return -1;
> + }
> +
> + skip = rc;
> + }
> + return 0;
> +}
> +
> /** sockaddr_ntop() - Convert a socket address to text format
> * @sa: Socket address
> * @dst: output buffer, minimum SOCKADDR_STRLEN bytes
> diff --git a/util.h b/util.h
> index d02333d..73a7a33 100644
> --- a/util.h
> +++ b/util.h
> @@ -203,6 +203,8 @@ int fls(unsigned long x);
> int write_file(const char *path, const char *buf);
> int write_all_buf(int fd, const void *buf, size_t len);
> int write_remainder(int fd, const struct iovec *iov, size_t iovcnt, size_t skip);
> +int read_all_buf(int fd, void *buf, size_t len);
> +int read_remainder(int fd, struct iovec *iov, size_t cnt, size_t skip);
> void close_open_files(int argc, char **argv);
> bool snprintf_check(char *str, size_t size, const char *format, ...);
>
--
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
[-- Attachment #2: signature.asc --]
[-- Type: application/pgp-signature, Size: 833 bytes --]
next prev parent reply other threads:[~2025-01-29 4:00 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-01-28 23:39 [PATCH v2 0/8] Draft, incomplete series introducing state migration Stefano Brivio
2025-01-28 23:39 ` [PATCH v2 1/8] icmp, udp: Pad time_t timestamp to 64-bit to ease " Stefano Brivio
2025-01-29 1:34 ` David Gibson
2025-01-28 23:39 ` [PATCH v2 2/8] flow, flow_table: Pad flow table entries to 128 bytes, hash entries to 32 bits Stefano Brivio
2025-01-29 1:35 ` David Gibson
2025-01-28 23:39 ` [PATCH v2 3/8] flow_table: Use size in extern declaration for flowtab Stefano Brivio
2025-01-28 23:39 ` [PATCH v2 4/8] util: Add read_remainder() and read_all_buf() Stefano Brivio
2025-01-29 1:37 ` David Gibson [this message]
2025-01-28 23:39 ` [PATCH v2 5/8] Introduce facilities for guest migration on top of vhost-user infrastructure Stefano Brivio
2025-01-29 5:41 ` David Gibson
2025-01-29 8:46 ` Stefano Brivio
2025-01-30 1:28 ` David Gibson
2025-01-28 23:39 ` [PATCH v2 6/8] Introduce passt-repair Stefano Brivio
2025-01-28 23:39 ` [PATCH v2 7/8] Add interfaces and configuration bits for passt-repair Stefano Brivio
2025-01-29 6:09 ` David Gibson
2025-01-29 8:46 ` Stefano Brivio
2025-01-30 1:33 ` David Gibson
2025-01-28 23:39 ` [PATCH v2 8/8] flow, tcp: Basic pre-migration source handler to dump sequence numbers Stefano Brivio
2025-01-29 6:15 ` David Gibson
2025-01-29 8:46 ` Stefano Brivio
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=Z5mGZIBnsYG9IEr8@zatzit \
--to=david@gibson.dropbear.id.au \
--cc=lvivier@redhat.com \
--cc=passt-dev@passt.top \
--cc=sbrivio@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
Code repositories for project(s) associated with this public inbox
https://passt.top/passt
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for IMAP folder(s).