[PATCH v11 06/10] io_uring: introduce attributes for read/write and PI support

[Anuj Gupta]

On Mon, Dec 02, 2024 at 09:13:14PM -0500, Martin K. Petersen wrote:
> 
> I have things running on my end on top of Jens' tree (without error
> injection, that's to come).
> 
> One question, though: How am I to determine that the kernel supports
> attr_ptr and IORING_RW_ATTR_FLAG_PI? Now that we no longer have separate
> IORING_OP_{READ,WRITE}_META commands I can't use IO_URING_OP_SUPPORTED
> to find out whether the running kernel supports PI passthrough.

Martin, right currently there is no way to probe whether the kernel
supports read/write attributes or not.

Jens, Pavel how about introducing a new IO_URING_OP_* flag (something
like IO_URING_OP_RW_ATTR_SUPPORTED) to probe whether read/write attributes
are supported or not. Something like this [*]

[*]
diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 38f0d6b10eaf..787a2df8037f 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -723,6 +723,7 @@ struct io_uring_rsrc_update2 {
 #define IORING_REGISTER_FILES_SKIP	(-2)
 
 #define IO_URING_OP_SUPPORTED	(1U << 0)
+#define IO_URING_OP_RW_ATTR_SUPPORTED	(1U << 1)
 
 struct io_uring_probe_op {
 	__u8 op;
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index 3de75eca1c92..64e1e5d48dec 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -67,6 +67,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
 		.vectored		= 1,
+		.rw_attr		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_readv,
 		.issue			= io_read,
@@ -82,6 +83,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
 		.vectored		= 1,
+		.rw_attr		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_writev,
 		.issue			= io_write,
@@ -101,6 +103,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.ioprio			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
+		.rw_attr		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_read_fixed,
 		.issue			= io_read,
@@ -115,6 +118,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.ioprio			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
+		.rw_attr		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_write_fixed,
 		.issue			= io_write,
@@ -246,6 +250,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.ioprio			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
+		.rw_attr		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_read,
 		.issue			= io_read,
@@ -260,6 +265,7 @@ const struct io_issue_def io_issue_defs[] = {
 		.ioprio			= 1,
 		.iopoll			= 1,
 		.iopoll_queue		= 1,
+		.rw_attr		= 1,
 		.async_size		= sizeof(struct io_async_rw),
 		.prep			= io_prep_write,
 		.issue			= io_write,
diff --git a/io_uring/opdef.h b/io_uring/opdef.h
index 14456436ff74..61460c762ea7 100644
--- a/io_uring/opdef.h
+++ b/io_uring/opdef.h
@@ -27,6 +27,8 @@ struct io_issue_def {
 	unsigned		iopoll_queue : 1;
 	/* vectored opcode, set if 1) vectored, and 2) handler needs to know */
 	unsigned		vectored : 1;
+	/* supports rw attributes */
+	unsigned		rw_attr : 1;
 
 	/* size of async data needed, if any */
 	unsigned short		async_size;
diff --git a/io_uring/register.c b/io_uring/register.c
index f1698c18c7cb..a54aeaec116c 100644
--- a/io_uring/register.c
+++ b/io_uring/register.c
@@ -60,8 +60,11 @@ static __cold int io_probe(struct io_ring_ctx *ctx, void __user *arg,
 
 	for (i = 0; i < nr_args; i++) {
 		p->ops[i].op = i;
-		if (io_uring_op_supported(i))
+		if (io_uring_op_supported(i)) {
 			p->ops[i].flags = IO_URING_OP_SUPPORTED;
+			if (io_issue_defs[i].rw_attr)
+				p->ops[i].flags |= IO_URING_OP_RW_ATTR_SUPPORTED;
+		}
 	}
 	p->ops_len = i;
 
-- 
2.25.1