[PATCH 3/3] io_uring: add support for getdents

[Hao Xu <hao.xu@linux.dev>]

From: Hao Xu <howeyxu@tencent.com>

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.

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.

Co-developed-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>
Signed-off-by: Hao Xu <howeyxu@tencent.com>
---
 include/uapi/linux/io_uring.h |  7 ++++
 io_uring/fs.c                 | 60 +++++++++++++++++++++++++++++++++++
 io_uring/fs.h                 |  3 ++
 io_uring/opdef.c              |  8 +++++
 4 files changed, 78 insertions(+)

diff --git a/include/uapi/linux/io_uring.h b/include/uapi/linux/io_uring.h
index 08720c7bd92f..6c0d521135a6 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 */
@@ -235,6 +236,7 @@ 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,
@@ -273,6 +275,11 @@ 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..77f00577e09c 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 +298,56 @@ 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);
+
+	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);
+	struct file *file;
+	unsigned long getdents_flags = 0;
+	bool force_nonblock = issue_flags & IO_URING_F_NONBLOCK;
+	bool should_lock = false;
+	int ret;
+
+	if (force_nonblock) {
+		if (!(req->file->f_mode & FMODE_NOWAIT))
+			return -EAGAIN;
+
+		getdents_flags = DIR_CONTEXT_F_NOWAIT;
+	}
+
+	file = req->file;
+	if (file && (file->f_mode & FMODE_ATOMIC_POS)) {
+		if (file_count(file) > 1)
+			should_lock = true;
+	}
+	if (should_lock) {
+		if (!force_nonblock)
+			mutex_lock(&file->f_pos_lock);
+		else if (!mutex_trylock(&file->f_pos_lock))
+			return -EAGAIN;
+	}
+
+	ret = vfs_getdents(file, gd->dirent, gd->count, getdents_flags);
+	if (should_lock)
+		mutex_unlock(&file->f_pos_lock);
+
+	if (ret == -EAGAIN && force_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 3b9c6489b8b6..1bae6b2a8d0b 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)
-- 
2.25.1