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From:   Dominique Martinet <asmadeus@codewreck.org>
Date:   Wed, 10 May 2023 19:52:51 +0900
Subject: [PATCH v2 3/6] io_uring: add support for getdents
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Message-Id: <20230422-uring-getdents-v2-3-2db1e37dc55e@codewreck.org>
References: <20230422-uring-getdents-v2-0-2db1e37dc55e@codewreck.org>
In-Reply-To: <20230422-uring-getdents-v2-0-2db1e37dc55e@codewreck.org>
To:     Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        Jens Axboe <axboe@kernel.dk>,
        Pavel Begunkov <asml.silence@gmail.com>,
        Stefan Roesch <shr@fb.com>
Cc:     Clay Harris <bugs@claycon.org>, Dave Chinner <david@fromorbit.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        io-uring@vger.kernel.org,
        Dominique Martinet <asmadeus@codewreck.org>
Precedence: bulk

This add support for getdents64 to io_uring, acting exactly like the
syscall: the directory is iterated from it's current's position as
stored in the file struct, and the file's position is updated exactly as
if getdents64 had been called.

Additionally, since io_uring has no way of issuing a seek, a flag
IORING_GETDENTS_REWIND has been added that will seek to the start of the
directory like rewinddir(3) for users that might require such a thing.
This will act exactly as if seek then getdents64 have been called
sequentially with no atomicity guarantee:
if this wasn't clear it is the responsibility of the caller to not use
getdents multiple time on a single file in parallel if they want useful
results, as is currently the case when using the syscall from multiple
threads.

For filesystems that support NOWAIT in iterate_shared(), try to use it
first; if a user already knows the filesystem they use do not support
nowait they can force async through IOSQE_ASYNC in the sqe flags,
avoiding the need to bounce back through a useless EAGAIN return.
(Note we already do that in prep if rewind is requested)

Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
---
 include/uapi/linux/io_uring.h |  7 ++++++
 io_uring/fs.c                 | 57 +++++++++++++++++++++++++++++++++++++++++++
 io_uring/fs.h                 |  3 +++
 io_uring/opdef.c              |  8 ++++++
 4 files changed, 75 insertions(+)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 0716cb17e436..35d0de18d893 100644
--- a/include/uapi/linux/io_uring.h
+++ b/include/uapi/linux/io_uring.h
@@ -65,6 +65,7 @@ struct io_uring_sqe {
 		__u32		xattr_flags;
 		__u32		msg_ring_flags;
 		__u32		uring_cmd_flags;
+		__u32		getdents_flags;
 	};
 	__u64	user_data;	/* data to be passed back at completion time */
 	/* pack this to avoid bogus arm OABI complaints */
@@ -223,6 +224,7 @@ enum io_uring_op {
 	IORING_OP_URING_CMD,
 	IORING_OP_SEND_ZC,
 	IORING_OP_SENDMSG_ZC,
+	IORING_OP_GETDENTS,
 
 	/* this goes last, obviously */
 	IORING_OP_LAST,
@@ -259,6 +261,11 @@ enum io_uring_op {
  */
 #define SPLICE_F_FD_IN_FIXED	(1U << 31) /* the last bit of __u32 */
 
+/*
+ * sqe->getdents_flags
+ */
+#define IORING_GETDENTS_REWIND	(1U << 0)
+
 /*
  * POLL_ADD flags. Note that since sqe->poll_events is the flag space, the
  * command flags for POLL_ADD are stored in sqe->len.
diff --git a/io_uring/fs.c b/io_uring/fs.c
index f6a69a549fd4..b15ec81c1ed2 100644
--- a/io_uring/fs.c
+++ b/io_uring/fs.c
@@ -47,6 +47,13 @@ struct io_link {
 	int				flags;
 };
 
+struct io_getdents {
+	struct file			*file;
+	struct linux_dirent64 __user	*dirent;
+	unsigned int			count;
+	int				flags;
+};
+
 int io_renameat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
 {
 	struct io_rename *ren = io_kiocb_to_cmd(req, struct io_rename);
@@ -291,3 +298,53 @@ void io_link_cleanup(struct io_kiocb *req)
 	putname(sl->oldpath);
 	putname(sl->newpath);
 }
+
+int io_getdents_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe)
+{
+	struct io_getdents *gd = io_kiocb_to_cmd(req, struct io_getdents);
+
+	if (READ_ONCE(sqe->off) != 0)
+		return -EINVAL;
+
+	gd->dirent = u64_to_user_ptr(READ_ONCE(sqe->addr));
+	gd->count = READ_ONCE(sqe->len);
+	gd->flags = READ_ONCE(sqe->getdents_flags);
+	if (gd->flags & ~IORING_GETDENTS_REWIND)
+		return -EINVAL;
+	/* rewind cannot be nowait */
+	if (gd->flags & IORING_GETDENTS_REWIND)
+		req->flags |= REQ_F_FORCE_ASYNC;
+
+	return 0;
+}
+
+int io_getdents(struct io_kiocb *req, unsigned int issue_flags)
+{
+	struct io_getdents *gd = io_kiocb_to_cmd(req, struct io_getdents);
+	unsigned long getdents_flags = 0;
+	int ret;
+
+	if (issue_flags & IO_URING_F_NONBLOCK) {
+		if (!(req->file->f_mode & FMODE_NOWAIT))
+			return -EAGAIN;
+
+		getdents_flags = DIR_CONTEXT_F_NOWAIT;
+	}
+	if ((gd->flags & IORING_GETDENTS_REWIND)) {
+		WARN_ON_ONCE(issue_flags & IO_URING_F_NONBLOCK);
+
+		ret = vfs_llseek(req->file, 0, SEEK_SET);
+		if (ret < 0)
+			goto out;
+	}
+
+	ret = vfs_getdents(req->file, gd->dirent, gd->count, getdents_flags);
+out:
+	if (ret == -EAGAIN &&
+	    (issue_flags & IO_URING_F_NONBLOCK))
+			return -EAGAIN;
+
+	io_req_set_res(req, ret, 0);
+	return 0;
+}
+
diff --git a/io_uring/fs.h b/io_uring/fs.h
index 0bb5efe3d6bb..f83a6f3a678d 100644
--- a/io_uring/fs.h
+++ b/io_uring/fs.h
@@ -18,3 +18,6 @@ int io_symlinkat(struct io_kiocb *req, unsigned int issue_flags);
 int io_linkat_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
 int io_linkat(struct io_kiocb *req, unsigned int issue_flags);
 void io_link_cleanup(struct io_kiocb *req);
+
+int io_getdents_prep(struct io_kiocb *req, const struct io_uring_sqe *sqe);
+int io_getdents(struct io_kiocb *req, unsigned int issue_flags);
diff --git a/io_uring/opdef.c b/io_uring/opdef.c
index cca7c5b55208..8f770c582ab3 100644
--- a/io_uring/opdef.c
+++ b/io_uring/opdef.c
@@ -428,6 +428,11 @@ const struct io_issue_def io_issue_defs[] = {
 		.prep			= io_eopnotsupp_prep,
 #endif
 	},
+	[IORING_OP_GETDENTS] = {
+		.needs_file		= 1,
+		.prep			= io_getdents_prep,
+		.issue			= io_getdents,
+	},
 };
 
 
@@ -648,6 +653,9 @@ const struct io_cold_def io_cold_defs[] = {
 		.fail			= io_sendrecv_fail,
 #endif
 	},
+	[IORING_OP_GETDENTS] = {
+		.name			= "GETDENTS",
+	},
 };
 
 const char *io_uring_get_opcode(u8 opcode)

-- 
2.39.2