[PATCHSET 0/4] Allow allocated direct descriptors

[PATCHSET 0/4] Allow allocated direct descriptors

[Jens Axboe]

Hi,

Currently using direct descriptors with open or accept requires the
application to manage the descriptor space, picking which slot to use
for any given file. However, there are cases where it's useful to just
get a direct descriptor and not care about which value it is, instead
just return it like a normal open or accept would.

This will also be useful for multishot accept support, where allocated
direct descriptors are a requirement to make that feature work with
these kinds of files.

This adds support for allocating a new fixed descriptor. This is chosen
by passing in UINT_MAX as the fixed slot, which otherwise has a limit
of INT_MAX like any file descriptor does.

 fs/io_uring.c | 100 +++++++++++++++++++++++++++++++++++++++++++++++---
  1 file changed, 94 insertions(+), 6 deletions(-)

-- 
Jens Axboe

[PATCH 1/4] io_uring: track fixed files with a bitmap

[Jens Axboe]

In preparation for adding a basic allocator for direct descriptors,
add helpers that set/clear whether a file slot is used.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index b6d491c9a25f..6eac6629e7d4 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -257,6 +257,7 @@ struct io_rsrc_put {
 
 struct io_file_table {
 	struct io_fixed_file *files;
+	unsigned long *bitmap;
 };
 
 struct io_rsrc_node {
@@ -7573,6 +7574,7 @@ static inline struct file *io_file_get_fixed(struct io_kiocb *req, int fd,
 	/* mask in overlapping REQ_F and FFS bits */
 	req->flags |= (file_ptr << REQ_F_SUPPORT_NOWAIT_BIT);
 	io_req_set_rsrc_node(req, ctx, 0);
+	WARN_ON_ONCE(file && !test_bit(fd, ctx->file_table.bitmap));
 out:
 	io_ring_submit_unlock(ctx, issue_flags);
 	return file;
@@ -8639,13 +8641,35 @@ static bool io_alloc_file_tables(struct io_file_table *table, unsigned nr_files)
 {
 	table->files = kvcalloc(nr_files, sizeof(table->files[0]),
 				GFP_KERNEL_ACCOUNT);
-	return !!table->files;
+	if (unlikely(!table->files))
+		return false;
+
+	table->bitmap = bitmap_zalloc(nr_files, GFP_KERNEL_ACCOUNT);
+	if (unlikely(!table->bitmap)) {
+		kvfree(table->files);
+		return false;
+	}
+
+	return true;
 }
 
 static void io_free_file_tables(struct io_file_table *table)
 {
 	kvfree(table->files);
+	bitmap_free(table->bitmap);
 	table->files = NULL;
+	table->bitmap = NULL;
+}
+
+static inline void io_file_bitmap_set(struct io_file_table *table, int bit)
+{
+	WARN_ON_ONCE(test_bit(bit, table->bitmap));
+	__set_bit(bit, table->bitmap);
+}
+
+static inline void io_file_bitmap_clear(struct io_file_table *table, int bit)
+{
+	__clear_bit(bit, table->bitmap);
 }
 
 static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
@@ -8660,6 +8684,7 @@ static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
 			continue;
 		if (io_fixed_file_slot(&ctx->file_table, i)->file_ptr & FFS_SCM)
 			continue;
+		io_file_bitmap_clear(&ctx->file_table, i);
 		fput(file);
 	}
 #endif
@@ -9063,6 +9088,7 @@ static int io_sqe_files_register(struct io_ring_ctx *ctx, void __user *arg,
 		}
 		file_slot = io_fixed_file_slot(&ctx->file_table, i);
 		io_fixed_file_set(file_slot, file);
+		io_file_bitmap_set(&ctx->file_table, i);
 	}
 
 	io_rsrc_node_switch(ctx, NULL);
@@ -9123,6 +9149,7 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 		if (ret)
 			goto err;
 		file_slot->file_ptr = 0;
+		io_file_bitmap_clear(&ctx->file_table, slot_index);
 		needs_switch = true;
 	}
 
@@ -9130,13 +9157,16 @@ static int io_install_fixed_file(struct io_kiocb *req, struct file *file,
 	if (!ret) {
 		*io_get_tag_slot(ctx->file_data, slot_index) = 0;
 		io_fixed_file_set(file_slot, file);
+		io_file_bitmap_set(&ctx->file_table, slot_index);
 	}
 err:
 	if (needs_switch)
 		io_rsrc_node_switch(ctx, ctx->file_data);
 	io_ring_submit_unlock(ctx, issue_flags);
-	if (ret)
+	if (ret) {
+		io_file_bitmap_clear(&ctx->file_table, slot_index);
 		fput(file);
+	}
 	return ret;
 }
 
@@ -9171,6 +9201,7 @@ static int io_close_fixed(struct io_kiocb *req, unsigned int issue_flags)
 		goto out;
 
 	file_slot->file_ptr = 0;
+	io_file_bitmap_clear(&ctx->file_table, offset);
 	io_rsrc_node_switch(ctx, ctx->file_data);
 	ret = 0;
 out:
@@ -9220,6 +9251,7 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 			if (err)
 				break;
 			file_slot->file_ptr = 0;
+			io_file_bitmap_clear(&ctx->file_table, i);
 			needs_switch = true;
 		}
 		if (fd != -1) {
@@ -9248,6 +9280,7 @@ static int __io_sqe_files_update(struct io_ring_ctx *ctx,
 			}
 			*io_get_tag_slot(data, i) = tag;
 			io_fixed_file_set(file_slot, file);
+			io_file_bitmap_set(&ctx->file_table, i);
 		}
 	}
 
-- 
2.35.1

[PATCH 2/4] io_uring: add basic fixed file allocator

[Jens Axboe]

Applications currently always pick where they want fixed files to go.
In preparation for allowing these types of commands with multishot
support, add a basic allocator in the fixed file table.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6eac6629e7d4..6148bd562add 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -258,6 +258,7 @@ struct io_rsrc_put {
 struct io_file_table {
 	struct io_fixed_file *files;
 	unsigned long *bitmap;
+	unsigned int alloc_hint;
 };
 
 struct io_rsrc_node {
@@ -4696,6 +4697,31 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return __io_openat_prep(req, sqe);
 }
 
+static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
+{
+	struct io_file_table *table = &ctx->file_table;
+	unsigned long nr = ctx->nr_user_files;
+	int ret;
+
+	if (table->alloc_hint >= nr)
+		table->alloc_hint = 0;
+
+	do {
+		ret = find_next_zero_bit(table->bitmap, nr, table->alloc_hint);
+		if (ret != nr) {
+			table->alloc_hint = ret + 1;
+			return ret;
+		}
+		if (!table->alloc_hint)
+			break;
+
+		nr = table->alloc_hint;
+		table->alloc_hint = 0;
+	} while (1);
+
+	return -ENFILE;
+}
+
 static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct open_flags op;
@@ -8665,11 +8691,14 @@ static inline void io_file_bitmap_set(struct io_file_table *table, int bit)
 {
 	WARN_ON_ONCE(test_bit(bit, table->bitmap));
 	__set_bit(bit, table->bitmap);
+	if (bit == table->alloc_hint)
+		table->alloc_hint++;
 }
 
 static inline void io_file_bitmap_clear(struct io_file_table *table, int bit)
 {
 	__clear_bit(bit, table->bitmap);
+	table->alloc_hint = bit;
 }
 
 static void __io_sqe_files_unregister(struct io_ring_ctx *ctx)
-- 
2.35.1

[PATCH 3/4] io_uring: allow allocated fixed files for openat/openat2

[Jens Axboe]

If the applications passes in UINT_MAX as the file_slot, then that's a
hint to allocate a fixed file descriptor rather than have one be passed
in directly.

This can be useful for having io_uring manage the direct descriptor space.

Normal open direct requests will complete with 0 for success, and < 0
in case of error. If io_uring is asked to allocated the direct descriptor,
then the direct descriptor is returned in case of success.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 32 +++++++++++++++++++++++++++++---
 1 file changed, 29 insertions(+), 3 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 6148bd562add..986a6e82bc09 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4697,7 +4697,7 @@ static int io_openat2_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 	return __io_openat_prep(req, sqe);
 }
 
-static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
+static int io_file_bitmap_get(struct io_ring_ctx *ctx)
 {
 	struct io_file_table *table = &ctx->file_table;
 	unsigned long nr = ctx->nr_user_files;
@@ -4722,6 +4722,32 @@ static int __maybe_unused io_file_bitmap_get(struct io_ring_ctx *ctx)
 	return -ENFILE;
 }
 
+static int io_fixed_file_install(struct io_kiocb *req, unsigned int issue_flags,
+				 struct file *file, unsigned int file_slot)
+{
+	int alloc_slot = file_slot == UINT_MAX;
+	struct io_ring_ctx *ctx = req->ctx;
+	int ret;
+
+	if (alloc_slot) {
+		io_ring_submit_lock(ctx, issue_flags);
+		file_slot = io_file_bitmap_get(ctx);
+		if (unlikely(file_slot < 0)) {
+			io_ring_submit_unlock(ctx, issue_flags);
+			return file_slot;
+		}
+	}
+
+	ret = io_install_fixed_file(req, file, issue_flags, file_slot);
+	if (alloc_slot) {
+		io_ring_submit_unlock(ctx, issue_flags);
+		if (!ret)
+			return file_slot;
+	}
+
+	return ret;
+}
+
 static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
 {
 	struct open_flags op;
@@ -4777,8 +4803,8 @@ static int io_openat2(struct io_kiocb *req, unsigned int issue_flags)
 	if (!fixed)
 		fd_install(ret, file);
 	else
-		ret = io_install_fixed_file(req, file, issue_flags,
-					    req->open.file_slot - 1);
+		ret = io_fixed_file_install(req, issue_flags, file,
+						req->open.file_slot);
 err:
 	putname(req->open.filename);
 	req->flags &= ~REQ_F_NEED_CLEANUP;
-- 
2.35.1

[PATCH 4/4] io_uring: allow allocated fixed files for accept

[Jens Axboe]

If the applications passes in UINT_MAX as the file_slot, then that's a
hint to allocate a fixed file descriptor rather than have one be passed
in directly.

This can be useful for having io_uring manage the direct descriptor space,
and also allows multi-shot support to work with fixed files.

Normal accept direct requests will complete with 0 for success, and < 0
in case of error. If io_uring is asked to allocated the direct descriptor,
then the direct descriptor is returned in case of success.

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/io_uring.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 986a6e82bc09..9fc38c749492 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -5802,8 +5802,8 @@ static int io_accept(struct io_kiocb *req, unsigned int issue_flags)
 		fd_install(fd, file);
 		ret = fd;
 	} else {
-		ret = io_install_fixed_file(req, file, issue_flags,
-					    accept->file_slot - 1);
+		ret = io_fixed_file_install(req, issue_flags, file,
+						accept->file_slot);
 	}
 	__io_req_complete(req, issue_flags, ret, 0);
 	return 0;
-- 
2.35.1