linux-kernel - [PATCH v2 0/3] fanotify accounting for fs/splice.c

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Date:   Tue, 27 Jun 2023 01:08:38 +0200
From:   наб <nabijaczleweli@...ijaczleweli.xyz>
To:     Amir Goldstein <amir73il@...il.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jan Kara <jack@...e.cz>,
        Chung-Chiang Cheng <cccheng@...ology.com>
Subject: [PATCH v2 0/3] fanotify accounting for fs/splice.c

"people just forget to add inotify hooks to their I/O routines as a rule"?
Guess what I did, fully knowing that some are missing in this file :)

==> te.c <==
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
int main() {
  ssize_t rd, acc = 0;
  while ((rd = tee(0, 1, 128 * 1024 * 1024, 0)) > 0)
    acc += rd;
  fprintf(stderr, "te=%zd: %m\n", acc);
}

==> vm.c <==
#define _GNU_SOURCE
#include <fcntl.h>
#include <stdio.h>
#include <string.h>
static char sb[1024 * 1024];
int main() {
  memcpy(sb, "żupan", sizeof("żupan"));
  ssize_t rd =
      vmsplice(1, &(struct iovec){.iov_base = sb, .iov_len = sizeof(sb)}, 1,
               SPLICE_F_GIFT);
  fprintf(stderr, "vm=%zd: %m\n", rd);
}


echo zupa | ./te > fifo tees a few times and then blocks when the pipe
fills, at which point we get into the broken state.

Similarly, ./vm > fifo (with the default 64k F_GETPIPE_SZ) enters that
same state instantly.

With 2/3 and 3/3, they instead do
  1: mask=2, cook=0, len=0, name=
  rd=80
  1: mask=2, cook=0, len=0, name=
  rd=80
  ...
in a loop, as-expected, and 
  # ./vm > fifo
  vm=65200: Success
  1: mask=2, cook=0, len=0, name=
  rd=65200

I took the liberty of marking 2/3 and 3/3 as Fixes: of the original
fanotify-in-splice commit as well, I think they fit the bill.

Ahelenia Ziemiańska (3):
  splice: always fsnotify_access(in), fsnotify_modify(out) on success
  splice: fsnotify_modify(fd) in vmsplice
  splice: fsnotify_access(in), fsnotify_modify(out) on success in tee

 fs/splice.c | 29 ++++++++++++++++++++---------
 1 file changed, 20 insertions(+), 9 deletions(-)

-- 
2.39.2

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