linux-kernel - Re: [PATCH v3 0/5] iov_iter: Adjust styling/location of new splice functions

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Message-ID: <2677038.1676389769@warthog.procyon.org.uk>
Date:   Tue, 14 Feb 2023 15:49:29 +0000
From:   David Howells <dhowells@...hat.com>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     dhowells@...hat.com, David Hildenbrand <david@...hat.com>,
        Al Viro <viro@...iv.linux.org.uk>,
        Christoph Hellwig <hch@...radead.org>,
        Matthew Wilcox <willy@...radead.org>, Jan Kara <jack@...e.cz>,
        Jeff Layton <jlayton@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Logan Gunthorpe <logang@...tatee.com>,
        Hillf Danton <hdanton@...a.com>, linux-fsdevel@...r.kernel.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH v3 0/5] iov_iter: Adjust styling/location of new splice functions

Jens Axboe <axboe@...nel.dk> wrote:

> That is indeed the question, and unanswered so far... Let's turn it into
> one clean series, and get it stuffed into for-next and most likely
> target 6.4 for inclusion at this point.

I was waiting to see if the patch worked for Daniel (which it does) and
Guenter (no answer yet) before answering.  It appears to fix shmem - I've
tested it with:

	dd if=/dev/zero of=/tmp/sparse count=1 seek=401 bs=4096
	just-splice /tmp/sparse 11234000 | sha1sum

where just-splice.c is attached (note that piping the output into another
program is important to make the splice work).

Meanwhile, I'm working on working the changes into my patchset at appropriate
points.

David
---
#define _GNU_SOURCE 
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/sendfile.h>
#include <sys/wait.h>

static char *prog;

int main(int argc, char *argv[])
{
        unsigned int iflags = 0;
        ssize_t spliced, remain;
        int in, out;

        prog = argv[0];
        if (argc > 1 && strcmp(argv[1], "-d") == 0) {
                iflags |= O_DIRECT;
                argv++;
                argc--;
        }

        if (argc != 3 || !argv[1][0] || !argv[2][0]) {
                fprintf(stderr, "Usage: %s <file> <amount>\n", prog);
                exit(2);
        }

        in = open(argv[1], O_RDONLY | O_NOFOLLOW | iflags);
        if (in < 0) {
                perror("open");
                exit(1);
        }

        remain = strtoul(argv[2], NULL, 0);
        while (remain > 0) {
                spliced = splice(in, NULL, 1, NULL, remain, 0);
                if (spliced < 0) {
                        perror("splice");
                        exit(1);
                }
                if (spliced == 0)
                        break;
                remain -= spliced;
        }

        exit(0);
}