SQPOLL behaviour with openat

PATCH [email protected] 2 participants 4 messages Jan 4, 2020 io_uring

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[email protected]

author

2020-01-04 16:22 UTC #0 lore raw

Hello,

I am trying to understand SQPOLL behaviour using liburing. I modified the test in liburing (see below). The test is failing when we use openat with SQPOLL:

cqe res -9
test_io failed 0/0/1/0/0

Is openat supported with SQPOLL? If not I would expect -EINVAL as a return value, but maybe I'm missing something.
note: I also tested without io_uring_register_files call.

Signature · 5 lines

William

---
 test/read-write.c | 47 ++++++++++++++++++++++++++++++++++++++++++++---
 1 file changed, 44 insertions(+), 3 deletions(-)

test/read-write.c +44 -3

index d150f44..05baf0f 100644
@@ -58,7 +58,7 @@ static int test_io(const char *file, int write, int buffered, int sqthread,
 	struct io_uring_cqe *cqe;
 	struct io_uring ring;
 	int open_flags, ring_flags;
-	int i, fd, ret;
+	int i, dirfd, fd, use_fd, ret;
 
 #ifdef VERBOSE
 	fprintf(stdout, "%s: start %d/%d/%d/%d/%d: ", __FUNCTION__, write,

@@ -79,7 +79,7 @@ static int test_io(const char *file, int write, int buffered, int sqthread,
 	if (!buffered)
 		open_flags |= O_DIRECT;
 
-	fd = open(file, open_flags);
+	dirfd = open(".", O_RDONLY);
 	if (fd < 0) {
 		perror("file open");
 		goto err;

@@ -95,6 +95,46 @@ static int test_io(const char *file, int write, int buffered, int sqthread,
 		goto err;
 	}
 
+	use_fd = dirfd;
+	if (sqthread) {
+		ret = io_uring_register_files(&ring, &dirfd, 1);
+		if (ret) {
+			fprintf(stderr, "file reg failed: %d\n", ret);
+			goto err;
+		}
+		use_fd = 0;
+	}
+	sqe = io_uring_get_sqe(&ring);
+	if (!sqe) {
+		fprintf(stderr, "sqe get failed\n");
+		goto err;
+	}
+	io_uring_prep_openat(sqe, use_fd, file, open_flags, 0);
+	ret = io_uring_submit(&ring);
+	if (ret != 1) {
+		fprintf(stderr, "submit got %d\n", ret);
+		goto err;
+	}
+	ret = io_uring_wait_cqe(&ring, &cqe);
+	if (ret) {
+		fprintf(stderr, "wait_cqe=%d\n", ret);
+		goto err;
+	}
+	if (cqe->res < 0) {
+		fprintf(stderr, "cqe res %d\n", cqe->res);
+		goto err;
+	}
+	fd = cqe->res;
+	io_uring_cqe_seen(&ring, cqe);
+
+	if (sqthread) {
+		ret = io_uring_unregister_files(&ring);
+		if (ret) {
+			fprintf(stderr, "file unreg failed: %d\n", ret);
+			goto err;
+		}
+	}
+
 	if (fixed) {
 		ret = io_uring_register_buffers(&ring, vecs, BUFFERS);
 		if (ret) {

@@ -121,7 +161,7 @@ static int test_io(const char *file, int write, int buffered, int sqthread,
 		offset = BS * (rand() % BUFFERS);
 		if (write) {
 			int do_fixed = fixed;
-			int use_fd = fd;
+			use_fd = fd;
 
 			if (sqthread)
 				use_fd = 0;

@@ -193,6 +233,7 @@ static int test_io(const char *file, int write, int buffered, int sqthread,
 
 	io_uring_queue_exit(&ring);
 	close(fd);
+	close(dirfd);
 #ifdef VERBOSE
 	printf("PASS\n");
 #endif

Signature · 1 line

2.24.1

Jens Axboe

maintainer

2020-01-04 16:28 UTC #1 lore raw

Quoted 6 lines · On 1/4/20 9:22 AM, [email protected] wrote:

Hello,
I am trying to understand SQPOLL behaviour using liburing. I modified the test in liburing (see below). The test is failing when we use openat with SQPOLL:

Quoted 6 lines

cqe res -9
test_io failed 0/0/1/0/0
Is openat supported with SQPOLL? If not I would expect -EINVAL as a return value, but maybe I'm missing something.
note: I also tested without io_uring_register_files call.

sqpoll requires the use of fixed files for any sqe, at least for now. That's why it returns -EBADF if the request doesn't have fixed files specified.

So it cannot be used with opcodes that create (or close) file descriptors either.

Signature · 1 line

Jens Axboe

William Dauchy

author

2020-01-04 16:42 UTC #2 lore raw

Hello Jens,

Thank you for the quick answer.

Quoted 3 lines · Jens Axboe

sqpoll requires the use of fixed files for any sqe, at least for now. That's why it returns -EBADF if the request doesn't have fixed files specified.

I indeed forgot sqe->flags |= IOSQE_FIXED_FILE; in my modified test.

Quoted 2 lines

So it cannot be used with opcodes that create (or close) file descriptors either.

ok, I thought dirfd could have been the index of my registered fd for openat call. It was not very clear to me this was not possible to use fixed files for those opcodes.

Thanks,

Signature · 1 line

William

Jens Axboe

maintainer

2020-01-04 17:41 UTC #3 lore raw

Quoted 9 lines · William Dauchy

Hello Jens,
Thank you for the quick answer.
Quoted 3 lines · Jens Axboe
sqpoll requires the use of fixed files for any sqe, at least for now. That's why it returns -EBADF if the request doesn't have fixed files specified.

Quoted 8 lines

I indeed forgot sqe->flags |= IOSQE_FIXED_FILE; in my modified test.
Quoted 2 lines
So it cannot be used with opcodes that create (or close) file descriptors either.
ok, I thought dirfd could have been the index of my registered fd for openat call. It was not very clear to me this was not possible to use fixed files for those opcodes.

I should probably clarify that in the man pages! I'll get that done. But yes, that it is how it _should_ work for registered files. I haven't spent too much time on sqpoll lately, but there's really no reason why it cannot do everything that the regular path can. Just need to ensure the proper inheritance is done, it's a kernel thread just like the async workers.

Signature · 1 line

Jens Axboe