Re: [PATCH] btrfs: add io_uring interface for encoded writes

[Jens Axboe <axboe@kernel.dk>]

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On 11/12/24 2:01 PM, Jens Axboe wrote:
> This is why io_kiocb->async_data exists. uring_cmd is already using that
> for the sqe, I think you'd want to add a 2nd "void *op_data" or
> something in there, and have the uring_cmd alloc cache get clear that to
> NULL and have uring_cmd alloc cache put kfree() it if it's non-NULL.
> 
> We'd also need to move the uring_cache struct into
> include/linux/io_uring_types.h so that btrfs can get to it (and probably
> rename it to something saner, uring_cmd_async_data for example).

Here are two patches that implement that basic thing on the io_uring
uring_cmd side. With that, you can then do:

> static int btrfs_uring_encoded_write(struct io_uring_cmd *cmd, unsigned int issue_flags)
> {
> 	struct io_kiocb *req = cmd_to_io_kiocb(cmd);
> 	struct uring_cmd_async_data *data = req->async_data;
> 	struct btrfs_ioctl_encoded_io_args *args;
> 
> 	if (!data->op_data) {
> 		data->op_data = kmalloc(sizeof(*args), GFP_NOIO);
> 		if (!data->op_data)
> 			return -ENOMEM;
> 		if (copy_from_user(data->op_data, sqe_addr, sizeof(*args))
> 			return -EFAULT;
> 	}
> 	...
> }

and have it be both stable, and not need to worry about freeing it
either. Hope that helps. Totally untested...

-- 
Jens Axboe

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From f06038764982dcf0440e2eef8073700becd8203d Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 12 Nov 2024 14:09:12 -0700
Subject: [PATCH 2/2] io_uring/cmd: add per-op data to struct io_uring_cmd_data

In case an op handler for ->uring_cmd() needs stable storage for user
data, it can allocate io_uring_cmd_data->op_data and use it for the
duration of the request. When the request gets cleaned up, uring_cmd
will free it automatically.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 include/linux/io_uring/cmd.h |  1 +
 io_uring/uring_cmd.c         | 13 +++++++++++--
 2 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 9541b8924e89..cb3a4c4f263c 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -20,6 +20,7 @@ struct io_uring_cmd {
 
 struct io_uring_cmd_data {
 	struct io_uring_sqe	sqes[2];
+	void			*op_data;
 };
 
 static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index a7a11cb5e22e..e676dae73a0f 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -23,12 +23,16 @@ static struct io_uring_cmd_data *io_uring_async_get(struct io_kiocb *req)
 
 	cache = io_alloc_cache_get(&ctx->uring_cache);
 	if (cache) {
+		cache->op_data = NULL;
 		req->flags |= REQ_F_ASYNC_DATA;
 		req->async_data = cache;
 		return cache;
 	}
-	if (!io_alloc_async_data(req))
-		return req->async_data;
+	if (!io_alloc_async_data(req)) {
+		cache = req->async_data;
+		cache->op_data = NULL;
+		return cache;
+	}
 	return NULL;
 }
 
@@ -37,6 +41,11 @@ static void io_req_uring_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
 	struct io_uring_cmd_data *cache = req->async_data;
 
+	if (cache->op_data) {
+		kfree(cache->op_data);
+		cache->op_data = NULL;
+	}
+
 	if (issue_flags & IO_URING_F_UNLOCKED)
 		return;
 	if (io_alloc_cache_put(&req->ctx->uring_cache, cache)) {
-- 
2.45.2


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From f444c9e2a6f1380419a9c1863f9048ae08a1b5c0 Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@kernel.dk>
Date: Tue, 12 Nov 2024 14:05:27 -0700
Subject: [PATCH 1/2] io_uring/cmd: rename struct uring_cache to
 io_uring_cmd_data

In preparation for making this more generically available for
->uring_cmd() usage that needs stable command data, rename it and move
it to io_uring/cmd.h instead.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 include/linux/io_uring/cmd.h |  4 ++++
 io_uring/io_uring.c          |  2 +-
 io_uring/uring_cmd.c         | 10 +++++-----
 io_uring/uring_cmd.h         |  4 ----
 4 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/include/linux/io_uring/cmd.h b/include/linux/io_uring/cmd.h
index 578a3fdf5c71..9541b8924e89 100644
--- a/include/linux/io_uring/cmd.h
+++ b/include/linux/io_uring/cmd.h
@@ -18,6 +18,10 @@ struct io_uring_cmd {
 	u8		pdu[32]; /* available inline for free use */
 };
 
+struct io_uring_cmd_data {
+	struct io_uring_sqe	sqes[2];
+};
+
 static inline const void *io_uring_sqe_cmd(const struct io_uring_sqe *sqe)
 {
 	return sqe->cmd;
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c
index 076171977d5e..f75bc2959f60 100644
--- a/io_uring/io_uring.c
+++ b/io_uring/io_uring.c
@@ -321,7 +321,7 @@ static __cold struct io_ring_ctx *io_ring_ctx_alloc(struct io_uring_params *p)
 	ret |= io_alloc_cache_init(&ctx->rw_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct io_async_rw));
 	ret |= io_alloc_cache_init(&ctx->uring_cache, IO_ALLOC_CACHE_MAX,
-			    sizeof(struct uring_cache));
+			    sizeof(struct io_uring_cmd_data));
 	spin_lock_init(&ctx->msg_lock);
 	ret |= io_alloc_cache_init(&ctx->msg_cache, IO_ALLOC_CACHE_MAX,
 			    sizeof(struct io_kiocb));
diff --git a/io_uring/uring_cmd.c b/io_uring/uring_cmd.c
index e9d99d3ecc34..a7a11cb5e22e 100644
--- a/io_uring/uring_cmd.c
+++ b/io_uring/uring_cmd.c
@@ -16,10 +16,10 @@
 #include "rsrc.h"
 #include "uring_cmd.h"
 
-static struct uring_cache *io_uring_async_get(struct io_kiocb *req)
+static struct io_uring_cmd_data *io_uring_async_get(struct io_kiocb *req)
 {
 	struct io_ring_ctx *ctx = req->ctx;
-	struct uring_cache *cache;
+	struct io_uring_cmd_data *cache;
 
 	cache = io_alloc_cache_get(&ctx->uring_cache);
 	if (cache) {
@@ -35,7 +35,7 @@ static struct uring_cache *io_uring_async_get(struct io_kiocb *req)
 static void io_req_uring_cleanup(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-	struct uring_cache *cache = req->async_data;
+	struct io_uring_cmd_data *cache = req->async_data;
 
 	if (issue_flags & IO_URING_F_UNLOCKED)
 		return;
@@ -179,7 +179,7 @@ static int io_uring_cmd_prep_setup(struct io_kiocb *req,
 				   const struct io_uring_sqe *sqe)
 {
 	struct io_uring_cmd *ioucmd = io_kiocb_to_cmd(req, struct io_uring_cmd);
-	struct uring_cache *cache;
+	struct io_uring_cmd_data *cache;
 
 	cache = io_uring_async_get(req);
 	if (unlikely(!cache))
@@ -256,7 +256,7 @@ int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags)
 
 	ret = file->f_op->uring_cmd(ioucmd, issue_flags);
 	if (ret == -EAGAIN) {
-		struct uring_cache *cache = req->async_data;
+		struct io_uring_cmd_data *cache = req->async_data;
 
 		if (ioucmd->sqe != (void *) cache)
 			memcpy(cache, ioucmd->sqe, uring_sqe_size(req->ctx));
diff --git a/io_uring/uring_cmd.h b/io_uring/uring_cmd.h
index 7dba0f1efc58..f6837ee0955b 100644
--- a/io_uring/uring_cmd.h
+++ b/io_uring/uring_cmd.h
@@ -1,9 +1,5 @@
 // SPDX-License-Identifier: GPL-2.0
 
-struct uring_cache {
-	struct io_uring_sqe sqes[2];
-};
-
 int io_uring_cmd(struct io_kiocb *req, unsigned int issue_flags);
 int io_uring_cmd_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 
-- 
2.45.2