[PATCH] io_uring: add IORING_OP_NOP_FAIL

[PATCH] io_uring: add IORING_OP_NOP_FAIL

[Ming Lei]

Add IORING_OP_NOP_FAIL so that it is easy to inject failure from
userspace.

Like IORING_OP_NOP, the main use case is test, and it is very helpful
for covering failure handling code in io_uring core change.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
---
 include/uapi/linux/io_uring.h |  2 ++
 io_uring/nop.c                | 27 +++++++++++++++++++++++++++
 io_uring/nop.h                |  3 +++
 io_uring/opdef.c              |  9 +++++++++
 4 files changed, 41 insertions(+)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 922f29b07ccc..18e58477e0f0 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -72,6 +72,7 @@ struct io_uring_sqe {
 		__u32		waitid_flags;
 		__u32		futex_flags;
 		__u32		install_fd_flags;
+		__s32		nop_fail_res;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	/* pack this to avoid bogus arm OABI complaints */
@@ -259,6 +260,7 @@ enum io_uring_op {
 	IORING_OP_FUTEX_WAITV,
 	IORING_OP_FIXED_FD_INSTALL,
 	IORING_OP_FTRUNCATE,
+	IORING_OP_NOP_FAIL,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
diff --git a/io_uring/nop.c b/io_uring/nop.c
index d956599a3c1b..c30547e53b5c 100644
--- a/io_uring/nop.c
+++ b/io_uring/nop.c
@@ -10,6 +10,12 @@
 #include "io_uring.h"
 #include "nop.h"
 
+struct io_nop_fail {
+	/* NOTE: kiocb has the file as the first member, so don't do it here */
+	struct file	*file;
+	int		res;
+};
+
 int io_nop_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	return 0;
@@ -23,3 +29,24 @@ int io_nop(struct io_kiocb *req, unsigned int issue_flags)
 	io_req_set_res(req, 0, 0);
 	return IOU_OK;
 }
+
+int io_nop_fail_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_nop_fail *nf = io_kiocb_to_cmd(req, struct io_nop_fail);
+
+	nf->res = READ_ONCE(sqe->nop_fail_res);
+	return 0;
+}
+
+/*
+ * IORING_OP_NOP just posts a completion event, nothing else.
+ */
+int io_nop_fail(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_nop_fail *nf = io_kiocb_to_cmd(req, struct io_nop_fail);
+
+	if (nf->res < 0)
+		req_set_fail(req);
+	io_req_set_res(req, nf->res, 0);
+	return IOU_OK;
+}
diff --git a/io_uring/nop.h b/io_uring/nop.h
index 97f1535c9dec..ef40d3b15899 100644
--- a/io_uring/nop.h
+++ b/io_uring/nop.h
@@ -2,3 +2,6 @@
 
 int io_nop_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_nop(struct io_kiocb *req, unsigned int issue_flags);
+
+int io_nop_fail_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_nop_fail(struct io_kiocb *req, unsigned int issue_flags);
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 92b657a063a0..eadc5a12ee06 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -56,6 +56,12 @@ const struct io_issue_def io_issue_defs[] = {
 		.prep			= io_nop_prep,
 		.issue			= io_nop,
 	},
+	[IORING_OP_NOP_FAIL] = {
+		.audit_skip		= 1,
+		.iopoll			= 1,
+		.prep			= io_nop_fail_prep,
+		.issue			= io_nop_fail,
+	},
 	[IORING_OP_READV] = {
 		.needs_file		= 1,
 		.unbound_nonreg_file	= 1,
@@ -506,6 +512,9 @@ const struct io_cold_def io_cold_defs[] = {
 	[IORING_OP_NOP] = {
 		.name			= "NOP",
 	},
+	[IORING_OP_NOP_FAIL] = {
+		.name			= "NOP_FAIL",
+	},
 	[IORING_OP_READV] = {
 		.name			= "READV",
 		.cleanup		= io_readv_writev_cleanup,
-- 
2.44.0

Re: [PATCH] io_uring: add IORING_OP_NOP_FAIL

[Jens Axboe]

On 5/8/24 8:34 PM, Ming Lei wrote:
> Add IORING_OP_NOP_FAIL so that it is easy to inject failure from
> userspace.
> 
> Like IORING_OP_NOP, the main use case is test, and it is very helpful
> for covering failure handling code in io_uring core change.

Rather than use a new opcode for this, why don't we just add it to
the existing NOP? I know we don't check for flags in currently, so
you would not know if it worked, but we could add that and just
backport that one-liner as well.

And if we had such a flag, the fail res could be passed in as well.

-- 
Jens Axboe

Re: [PATCH] io_uring: add IORING_OP_NOP_FAIL

[Ming Lei]

On Wed, May 08, 2024 at 08:55:09PM -0600, Jens Axboe wrote:
> On 5/8/24 8:34 PM, Ming Lei wrote:
> > Add IORING_OP_NOP_FAIL so that it is easy to inject failure from
> > userspace.
> > 
> > Like IORING_OP_NOP, the main use case is test, and it is very helpful
> > for covering failure handling code in io_uring core change.
> 
> Rather than use a new opcode for this, why don't we just add it to
> the existing NOP? I know we don't check for flags in currently, so
> you would not know if it worked, but we could add that and just
> backport that one-liner as well.

Yeah, it is just for avoiding to break existed tests which may not build
over liburing.

I will switch to this way, looks one-line backporting can solve it.

> And if we had such a flag, the fail res could be passed in as well.

We can just pass the 'injected_fail_res' via sqe->len, meantime keep
'nop_flags' for error injection and future extension.


thanks,
Ming

Re: [PATCH] io_uring: add IORING_OP_NOP_FAIL

[Ming Lei]

On Thu, May 9, 2024 at 11:05 AM Ming Lei <ming.lei@redhat.com> wrote:
>
> On Wed, May 08, 2024 at 08:55:09PM -0600, Jens Axboe wrote:
> > On 5/8/24 8:34 PM, Ming Lei wrote:
> > > Add IORING_OP_NOP_FAIL so that it is easy to inject failure from
> > > userspace.
> > >
> > > Like IORING_OP_NOP, the main use case is test, and it is very helpful
> > > for covering failure handling code in io_uring core change.
> >
> > Rather than use a new opcode for this, why don't we just add it to
> > the existing NOP? I know we don't check for flags in currently, so
> > you would not know if it worked, but we could add that and just
> > backport that one-liner as well.
>
> Yeah, it is just for avoiding to break existed tests which may not build
> over liburing.
>
> I will switch to this way, looks one-line backporting can solve it.

I guess backporting can't work, because application code expects
NOP to complete successfully with and w/o non-zero sqe->rw_flags.

However, the backport has to fail NOP in case of non-zero sqe->rw_flags.

Thanks.

Re: [PATCH] io_uring: add IORING_OP_NOP_FAIL

[Jens Axboe]

On 5/8/24 9:05 PM, Ming Lei wrote:
> On Wed, May 08, 2024 at 08:55:09PM -0600, Jens Axboe wrote:
>> On 5/8/24 8:34 PM, Ming Lei wrote:
>>> Add IORING_OP_NOP_FAIL so that it is easy to inject failure from
>>> userspace.
>>>
>>> Like IORING_OP_NOP, the main use case is test, and it is very helpful
>>> for covering failure handling code in io_uring core change.
>>
>> Rather than use a new opcode for this, why don't we just add it to
>> the existing NOP? I know we don't check for flags in currently, so
>> you would not know if it worked, but we could add that and just
>> backport that one-liner as well.
> 
> Yeah, it is just for avoiding to break existed tests which may not build
> over liburing.

Don't think that's a huge risk, if someone is using the raw interface
and just not clearing, they would run into issues with mixed command
usage anyway. And a pure nop test would be fine anyway, as everything
starts out cleared.

> I will switch to this way, looks one-line backporting can solve it.

Exactly, thanks!

>> And if we had such a flag, the fail res could be passed in as well.
> 
> We can just pass the 'injected_fail_res' via sqe->len, meantime keep
> 'nop_flags' for error injection and future extension.

Precisely.

-- 
Jens Axboe