From: Jens Axboe <axboe@kernel.dk>
To: Al Viro <viro@zeniv.linux.org.uk>
Cc: Jann Horn <jannh@google.com>,
linux-aio@kvack.org, linux-block@vger.kernel.org,
Linux API <linux-api@vger.kernel.org>,
hch@lst.de, jmoyer@redhat.com, avi@scylladb.com,
linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH 13/18] io_uring: add file set registration
Date: Thu, 7 Feb 2019 09:14:41 -0700 [thread overview]
Message-ID: <51f167c6-aacc-dd5b-4481-7168c6f8b413@kernel.dk> (raw)
In-Reply-To: <20190207040547.GX2217@ZenIV.linux.org.uk>
[-- Attachment #1: Type: text/plain, Size: 1524 bytes --]
On 2/6/19 9:05 PM, Al Viro wrote:
> On Wed, Feb 06, 2019 at 10:56:41AM -0700, Jens Axboe wrote:
>> On 2/5/19 6:01 PM, Al Viro wrote:
>>> On Tue, Feb 05, 2019 at 05:27:29PM -0700, Jens Axboe wrote:
>>>
>>>> This should be better, passes some basic testing, too:
>>>>
>>>> http://git.kernel.dk/cgit/linux-block/commit/?h=io_uring&id=01a93aa784319a02ccfa6523371b93401c9e0073
>>>>
>>>> Verified that we're grabbing the right refs, and don't hold any
>>>> ourselves. For the file registration, forbid registration of the
>>>> io_uring fd, as that is pointless and will introduce a loop regardless
>>>> of fd passing.
>>>
>>> *shrug*
>>>
>>> So pass it to AF_UNIX socket and register _that_ - does't change the
>>> underlying problem.
>>
>> Maybe I'm being dense here, but it's an f_op match. Should catch a
>> passed fd as well, correct?
>
> f_op match on _what_?
>
>> With that, how can there be a loop?
>
> io_uring_fd = ....
> socketpair(PF_UNIX, SOCK_STREAM, 0, sock_fds);
> register sock_fds[0] and sock_fds[1] to io_uring_fd
> send SCM_RIGHTS datagram with io_uring_fd to sock_fds[0]
> close sock_fds[0], sock_fds[1] and io_uring_fd
>
> And there's your unreachable loop.
I created a small app to do just that, and ran it and verified that
->release() is called and the io_uring is released as expected. This
is run on the current -git branch, which has a socket backing for
the io_uring fd itself, but not for the registered files.
What am I missing here? Attaching the program as a reference.
--
Jens Axboe
[-- Attachment #2: viro.c --]
[-- Type: text/x-csrc, Size: 2969 bytes --]
#include <stdio.h>
#include <stdlib.h>
#include <stddef.h>
#include <signal.h>
#include <inttypes.h>
#include <sys/types.h>
#include <sys/syscall.h>
#include <sys/socket.h>
#include <sys/wait.h>
#include <fcntl.h>
#include <unistd.h>
#include <string.h>
#include <linux/fs.h>
struct io_sqring_offsets {
__u32 head;
__u32 tail;
__u32 ring_mask;
__u32 ring_entries;
__u32 flags;
__u32 dropped;
__u32 array;
__u32 resv[3];
};
struct io_cqring_offsets {
__u32 head;
__u32 tail;
__u32 ring_mask;
__u32 ring_entries;
__u32 overflow;
__u32 cqes;
__u32 resv[4];
};
struct io_uring_params {
__u32 sq_entries;
__u32 cq_entries;
__u32 flags;
__u32 sq_thread_cpu;
__u32 sq_thread_idle;
__u32 resv[5];
struct io_sqring_offsets sq_off;
struct io_cqring_offsets cq_off;
};
#define IORING_REGISTER_FILES 2
#define __NR_sys_io_uring_setup 425
#define __NR_sys_io_uring_register 427
static int io_uring_register_files(int ring_fd, int fd1, int fd2)
{
__s32 *fds;
fds = calloc(2, sizeof(__s32));
fds[0] = fd1;
fds[1] = fd2;
return syscall(__NR_sys_io_uring_register, ring_fd,
IORING_REGISTER_FILES, fds, 2);
}
static int io_uring_setup(unsigned entries, struct io_uring_params *p)
{
return syscall(__NR_sys_io_uring_setup, entries, p);
}
static int get_ring_fd(void)
{
struct io_uring_params p;
int fd;
memset(&p, 0, sizeof(p));
fd = io_uring_setup(2, &p);
if (fd < 0) {
perror("io_uring_setup");
return -1;
}
return fd;
}
static void send_fd(int socket, int fd)
{
char buf[CMSG_SPACE(sizeof(fd))];
struct cmsghdr *cmsg;
struct msghdr msg;
memset(buf, 0, sizeof(buf));
memset(&msg, 0, sizeof(msg));
msg.msg_control = buf;
msg.msg_controllen = sizeof(buf);
cmsg = CMSG_FIRSTHDR(&msg);
cmsg->cmsg_level = SOL_SOCKET;
cmsg->cmsg_type = SCM_RIGHTS;
cmsg->cmsg_len = CMSG_LEN(sizeof(fd));
memmove(CMSG_DATA(cmsg), &fd, sizeof(fd));
msg.msg_controllen = CMSG_SPACE(sizeof(fd));
if (sendmsg(socket, &msg, 0) < 0)
perror("sendmsg");
}
static int recv_fd(int socket)
{
struct msghdr msg;
char c_buffer[256];
struct cmsghdr *cmsg;
int fd;
memset(&msg, 0, sizeof(msg));
msg.msg_control = c_buffer;
msg.msg_controllen = sizeof(c_buffer);
if (recvmsg(socket, &msg, 0) < 0)
perror("recvmsg\n");
cmsg = CMSG_FIRSTHDR(&msg);
memmove(&fd, CMSG_DATA(cmsg), sizeof(fd));
return fd;
}
int main(int argc, char *argv[])
{
int sp[2], pid, ring_fd, ret;
if (socketpair(AF_UNIX, SOCK_DGRAM, 0, sp) != 0) {
perror("Failed to create Unix-domain socket pair\n");
return 1;
}
ring_fd = get_ring_fd();
if (ring_fd < 0)
return 1;
ret = io_uring_register_files(ring_fd, sp[0], sp[1]);
if (ret < 0) {
perror("register files");
return 1;
}
pid = fork();
if (pid) {
printf("Sending fd %d\n", ring_fd);
send_fd(sp[0], ring_fd);
} else {
int fd;
fd = recv_fd(sp[1]);
printf("Got fd %d\n", fd);
close(fd);
}
usleep(500000);
close(ring_fd);
close(sp[0]);
close(sp[1]);
return 0;
}
next prev parent reply other threads:[~2019-02-07 16:14 UTC|newest]
Thread overview: 30+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190129192702.3605-1-axboe@kernel.dk>
[not found] ` <20190129192702.3605-14-axboe@kernel.dk>
2019-01-30 1:29 ` [PATCH 13/18] io_uring: add file set registration Jann Horn
2019-01-30 15:35 ` Jens Axboe
2019-02-04 2:56 ` Al Viro
2019-02-05 2:19 ` Jens Axboe
2019-02-05 17:57 ` Jens Axboe
2019-02-05 19:08 ` Jens Axboe
2019-02-06 0:27 ` Jens Axboe
2019-02-06 1:01 ` Al Viro
2019-02-06 17:56 ` Jens Axboe
2019-02-07 4:05 ` Al Viro
2019-02-07 16:14 ` Jens Axboe [this message]
2019-02-07 16:30 ` Al Viro
2019-02-07 16:35 ` Jens Axboe
2019-02-07 16:51 ` Al Viro
2019-02-06 0:56 ` Al Viro
2019-02-06 13:41 ` Jens Axboe
2019-02-07 4:00 ` Al Viro
2019-02-07 9:22 ` Miklos Szeredi
2019-02-07 13:31 ` Al Viro
2019-02-07 14:20 ` Miklos Szeredi
2019-02-07 15:20 ` Al Viro
2019-02-07 15:27 ` Miklos Szeredi
2019-02-07 16:26 ` Al Viro
2019-02-07 19:08 ` Miklos Szeredi
2019-02-07 18:45 ` Jens Axboe
2019-02-07 18:58 ` Jens Axboe
2019-02-11 15:55 ` Jonathan Corbet
2019-02-11 17:35 ` Al Viro
2019-02-11 20:33 ` Jonathan Corbet
2019-01-23 15:35 [PATCHSET v7] io_uring IO interface Jens Axboe
2019-01-23 15:35 ` [PATCH 13/18] io_uring: add file set registration Jens Axboe
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